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List of contents
CONTENTS
â
DBQ database query language
INTRODUCTION
Introduction
Overview of facilities
COMMANDS
Commands
Interaction
Procedures
Command files
Comments
Editing
File names
Selection expressions
Relational operators
Aliases
Notation
COMMAND REFERENCE
create
insert
update
print
find
import
export
extract
compress
sort
erase
rename
define
show
enter
set
help
exit
command file inclusion (@)
DATABASE MAINTENANCE
Introduction
Setting up
Security
Reformatting
USING THE DATABASE
General points
Query style
Making a log file
Joining multiple databases
Limits
REPORT FORMATTING
Report formatting
Field specifiers
Heading specification
Pause specification
Uses of format files
MESSAGES AND ERRORS
Introduction
Informational messages
Error messages
Other error situations
>PA
Introduction â
DBQ is a powerful structured query language modelled on query
language facilities available on large minicomputers.
It is
designed for use by those wanting an English like command
language to enter database manipulation commands, rather than a
menu driven interface.
Because of this it cannot be used
immediately by a complete novice in the same manner as menu
driven systems, but it is easy to learn the basic commands in a
few hours, and once learnt, it is considerably faster and more
flexible to use.
The commands operate against disk resident files. Because of
this, there is no need to load or save database
files
explicitly, and the system is more resilient to power failures.
However, due to the disk accessing, the processing is generally
slower than memory resident databases.
The query language provides a comprehensive set of functions for
the creation, maintenance and enquiry of the database format
supported by the DBQ system.
The query language is the prime means of interaction with the
database and it is important to become properly conversant with
the many powerful commands before undertaking any major work
using it.
Because there is a finite limit on memory, many features found
in more expensive databases have been left out of DBQ. Whilst
important,
these are by no means essential for personal
databases. Such features include full arithmetic capabilities
for updating fields and reporting, full report formatting with
control totals, validation of input data at entry and high speed
keyed access to data. Because of these, and other limitations,
the database should be considered unsuitable for large scale
commercial usage.
â
Overview of facilities â
Database level commands permit the creation of a database,
erasing a database, renaming a database, sorting a database on
one or more fields, importing and exporting database records
from and to external applications, and compressing a database to
remove any deleted records from it.
Record
level
commands
include the insertion of records
interactively or from a data file, the updating of selected
records, the deletion of selected records, the selection of
records into a working database, and the listing of selected
records in tabular form or in a form specified by a format
file.
Specific fields can be selected in the update, find and print
operations,
and it is possible to do a relational join
operation, whereby selected fields from two or more databases
can be selected from records matched on some field or fields in
the databases.
Sequences of commands and data can be input from a file, and
short sequences of commands can be defined as procedures, which
can be executed simply by use of a keyword.
In fact, simple
groups of words can be defined in this way allowing aliases for
keywords and keyword combinations.
The command files and
procedures can input variable data to be used in the evaluation
of the command file or procedure. Command files and procedures
can be nested to a certain level.
Various options can be set, allowing control of the case
sensitivity, causing a command file to be listed as it is
executed, and switching a log file in or out to permit keyboard
input to be logged for a number of purposes.
Also tabulations
can be split into pages, and the page length can be varied to
accommodate different lengths of paper or different print
formatting.
Full online help is provided, permitting selection by initial
letter of help topics.
The command line input uses the CPM+ line input facilities,
permitting full editing to be carried out on the current line,
including the copying of the previous command using ^W. You are
referred to the CPM+ documentation or the CPM+ help file for
more information on this.
The database is initially built to hold 10 records, but grows as
new records are added. Records are updated in situ, and are
deleted by flagging them as deleted. Deleted records can be
compressed out of the database, and for occasions where a
deletion selection was a bit too greedy it is possible to dump
the deleted records out to a file for subsequent editing and
re-input.
â
COMMANDSâ
This section details each command in turn, providing the format
of the command and details of the commands action.
An example
is also provided.
Interaction
Commands may be entered in free form. This means that line
termination has no special meaning, and any number of spaces or
tabs can be inserted at the start or end of a line or between
elements. A command may be broken over more than one line,
whereupon continuation prompts are issued to show that further
input is expected. Where the end of a command has to be
indicated, for example at the end of a print selection, either a
new command or the command terminator ";" may be used. More
than one command can be issued on the same line, although it is
usually prudent to let each command execute before issuing the
next in case of failure, and because an error will cause unused
input for a command to be rejected as a syntax error.
Procedures
Procedures provide a means of entering a predefined block of
text as input, identified by a name. They are included in the
input by simply using their name, and can be used at any point
of input where a keyword or identifier is expected.
They can
represent anything from a single word up to a set of commands,
and can contain statements within them to prompt for variable
data to be used when expanding them.
Command files
Command files are like procedures, but instead of fetching text
from memory, the text is input from a file.
The text can
represent anything a procedure can represent, and can also
contain prompting statements, for use as variable input, or as
pauses in the command file execution.
Comments
Comments can be put on any line after a number sign "#", this
usually being used for command files, or when logging the
input.
The comment acts as a command terminator, so cannot be
inserted halfway through a command.
Editing
Line input is done via the CP/M line input routine, permitting
editing to be done on the current input line, and the previous
line to be recalled. This is useful when entering a long query
line, as errors can be easily corrected. Data input for the
INSERT and UPDATE functions is also done via this routine.
File names
File names with extensions indicated can be entered simply as
the name without the extension, or if another extension is used,
they may be entered within quotes, whereupon this is used as the
full name.
Database names cannot under most circumstances be
entered as a string, and should always be entered as an
identifier. A drive prefix can be put on any filename in either
form, but a user area specifier is not permitted when entered in
identifier form.
Selection expressions
A selection expression is a relational expression involving one
or more database fields. A relational expression is simply a
comparison between a field and a value (or another field). The
types of comparison are called relational operators, and are
listed below.
A compound relational expression involving
brackets and the logical operators 'and' and 'or' can be used to
specify a complex selection. There follows some examples of
selection expressions:balance > 10000
name } "Smith"
sex = "male" and (age > 65 or age < 20)
Note that in the last example, the brackets are necessary to
join the two age comparisons together for use in the 'and'
operation, otherwise the 'age < 20' would be separate and would
satisfy the expression by itself.
Relational operators
The relational operators are as follows.
= Equals
> Greater than
< Less than
>= Greater than or equal to
<= Less than or equal to
<> Not equal to
} Contains (substring search)
For numeric fields, a numeric comparison is made. For character
fields, a lexicographic comparison is made using the ASCII
collating sequence.
For the contains operator, a string search
is done regardless of field type. The contains operator can be
used as a "contained in" operator by simply reversing the
operands (e.g. with "montuewed" } day).
Aliases
When specifying complex queries involving qualification of field
names, and when joining a database with itself, a
more
convenient way of specifying fieldnames and database names is
provided.
The alias notation permits a temporary name, or 'alias' to be
specified for field names or database names. This is done by
specifying the alias directly after the normal name, without the
comma separator used to specify elements in a list.
The alias
name can be used wherever the original name can be used, apart
from in the field list or database list used to specify the
aliases.
Typically it would be used in a selection expression,
or in a format file. The field alias is also used in the title
line in a tabulation, and as the field name in a current working
database created by a FIND command.
For example, to join a family database between name and parent
name, the following selection could be entered.
DBQ> print family.name, parents.age dads_age
DBQ> of family, family parents
DBQ> with family.parent = parents.name ;
This shows the database "family" being given an alias "parents"
to show which instance of the database the age in the print list
and the name in the comparison should come from. The parents
age field also has an alias specified "dads_age" to allow the
report produced to have a more applicable heading.
Notation
In this section, keywords are shown in uppercase, and other
identifiers are shown in lowercase. This is done to permit the
keywords to be easily identified, and does not imply that they
must be used in uppercase. In fact the examples show normal
command input in lowercase, and this is the recommended mode of
use.
Square brackets indicate optional elements of the command
language.
A second occurence of an element or set of elements
within square brackets generally indicates that the set can be
repeated a number of times.
>PA
CREATE database fieldname type size [scale] [fieldname type size [scale]]
ERASE database
RENAME database newname
INSERT database
DELETE selection ;
UPDATE fieldnames OF selection ;
PRINT [USING formatfile] fieldnames OF selection [INTO reportfile] ;
FIND fieldnames OF selection ;
SORT database BY fieldname [direction] [fieldname [direction]] ;
IMPORT datafile INTO database
EXPORT [DELETED] database [INTO datafile] ;
EXTRACT database [INTO definitionfile] ;
COMPRESS database
DEFINE procedure / ENTER procedure
SHOW {procedure} ;
SET [NO] [FOLD] [VERIFY] [LOG] [PAGE [pagelength]] ;
HELP
EXIT
Where identifiers are:database, newname :
fieldnames
:
qualfieldname
fieldname
:
type
:
size
:
scale
:
direction
:
selection
:
expression
:
comparison
:
primary
relation
:
procedure
:
pagelength
:
datafile
:
formatfile
:
reportfile
:
definitionfile
identifier
:
database file name (Identifier) (Ext. .DBQ)
qualfieldname[+] [, qualfieldname[+] ...] | all[+]
: [database.]fieldname
field name (identifier)
NUM | CHAR
1 to 12 NUM, 1 to 128 CHAR
0 to 10 for NUM fields only
ASC (default) | DESC
database [, database ... ] WITH expression
[NOT] comparison [AND | OR [NOT] comparison ...]
primary relation primary
: qualfieldname | string | number
= | > | < | >= | <= | <> | }
procedure name (Identifier)
length of paper in lines less 6 for heading
data file name (Identifier) (Ext. .DAT)
format file name (Identifier) (Ext. .FMT)
report file name (Identifier) (Ext. .REP)
: definition file (Identifier) (Ext. .DEF)
Alpha [ alpha | "_" ...]
>PA
CREATE
Syntax
CREATE database fieldname type size [scale] {fieldname ...};
Details
-
database is the database name
fieldname is a field name
type is the field type (CHAR | NUM)
size is the field length
scale is the scale (decimal places) to be used when printing
totals. The default value is 0 indicating an integer field
(no decimal places).
This scale is not used for field
storage, although it is indicated whenever a field is input or
updated. Stored decimal places beyond the scale are ignored
in totalling.
The field name, type, length (and scale
specified for each field in the record.
Example
if
required) are
create accounts name char 10 acc_num num 6 balance num 8 2 ;
This creates a database called "accounts", with three
name, acc_num and balance.
fields
-
>PA
INSERT
Syntax
INSERT database
Details
This command allows records to be inserted in the database. It
prompts for the fields in the record one by one. Brackets show
the width of the field.
[string] and <numeric> fields are
indicated by the type of bracket.
A number after <numeric>
brackets indicates the number of decimal places. The brackets
are only displayed as a visual guide, and the length shown is
not enforced on input, although any field input longer than the
width shown will be truncated when stored.
Pressing just ENTER on the first field terminates
displays the number of records inserted.
Example
DBQ> insert accounts
name
acc_num
balance
-----name
[john smith]
<123
>
<2.34
> 2
[
]
[ 1 records inserted ]
>PA
UPDATE
Syntax
UPDATE {fields | ALL } OF selection;
input,
and
Details
- fields is a field list
- selection is a record selection expression
This allows you to update the specified fields in the selected
records. The original value is printed first, and a prompt is
issued to allow a new value to be input. If no value is entered
before pressing ENTER, the original value is retained. After
all records selected have been updated, a count of records
updated is displayed.
Example
update balance of accounts with name = "john smith";
balance
= 2.34
balance
<
> 2
>PA
PRINT
SYNTAX
PRINT [USING filename] [{ fieldname[+],
fieldname[+] . . . | ALL[+] } OF] selection [INTO repname] ;
Details
-
USING filename indicates a format file (ext=.FMT) to be used
for output formatting.
field[+] is an optionally qualified field name with optional
totalling (+) specified for numeric fields.
ALL indicates all fields with optional totalling (+) of all
numeric fields.
selection is a record selection expression.
repname is the name of an output file (ext=.REP) to be used
instead of the terminal for output. (LST will cause output to
the printer).
For format file details, see the appropriate section.
If the format file is not used, output is tabulated under
headings in a fairly simple and straightforward manner.
If
totalling is specified, totals are printed for the selected
records at the end of the tabulation. Headings consist of the
field names forced to uppercase, with underscores changed to
spaces. Aliases can be used to give the fields alternative
headings.
Totalling is usually only specified for numeric fields, but
character fields with leading numerics can also be totalled if
required.
Example
print name, acc_num account, balance+ of accounts
with name } "smith";
NAME
ACCOUNT
BALANCE
==============================
a smith
23
12.34
j smith
124
100.30
kb smith
21
4.20
==============================
116.84
[ 3 records found ]
>PA
FIND
SYNTAX
FIND { field, field . . . | ALL } OF selection ;
Details
- field is an optionally qualified field name
- ALL indicates all fields and can be abbreviated to *
- selection is a record selection expression
Creates a
records.
database
called
"CURRENT"
containing the selected
This command is used to create a working collection of records
which can have sorts, selective deletions or prints made against
it.
It can also be used to cut down the processing necessary
when joining a number of databases.
It can also be used to reformat a database, although other means
are available to achieve this if fields are to be added (see the
section on reformatting).
The names of fields can be changed by the use of aliases.
Example
find name, acc_num account of accounts with name } "smith";
rename current smiths
print smiths;
This selects the name field and the acc_num field (renamed to
account) of those records containing the string "smith" in the
name. It then renames the current database as the database
"smiths", and prints it.
>PA
IMPORT
SYNTAX
IMPORT filename INTO database
Details
-
filename is the name of a data file (ext .DAT) containing the
values of the fields, one per line.
- database is the name of the database to append the records
to.
Example
DBQ> import accdata into accounts
NOTE
Data to be transferred from a BASIC program should simply be
output one field per line using successive PRINT statements.
e.g. Subroutine for outputting data, assuming
opened for output, and closed afterwards.
2000
2010
2020
2030
REM OUTPUT DATA FOR DATABASE
FOR IND% = 1 TO RECCOUNT%
PRINT #9,ACCNAME$(IND%)
PRINT #9,ACCNUM%(IND%)
stream
9
is
2040 PRINT #9,ACCBAL(IND%)
2050 NEXT IND%
2060 RETURN
>PA
EXPORT
SYNTAX
EXPORT [DELETED] database [INTO filename]
Details
- database is the name of the database to export records from
- filename is the name of a file (ext .DAT) to receive the
records.
If omitted, the records are written
to
the
terminal.
- the "DELETED" option exports those records that have been
marked as deleted since the file was created or compressed.
It is used to recover overambitious deletions.
- records are written to the output file one field per line.
Example
DBQ> export deleted accounts into deldata
>PA
EXTRACT
SYNTAX
EXTRACT database [INTO filename]
Details
- database is the name of a database
- filename is a file (ext .DEF) to receive the definition. If
omitted, the definition is written to the terminal - this is
handy for reminding you what fields are defined.
- The definition is specified as the commands necessary to
create the database again at the current size.
Example
DBQ> extract accounts
create accounts
name char 10
acc_num num 6
balance num 8 2
;
>PA
COMPRESS
SYNTAX
COMPRESS database
Details
- database is a database name.
This compresses active records at the start of the database
file, and frees up space at the end for further records to be
added.
Example
DBQ> compress accounts
[20 records freed]
NOTE
To reduce the size of the file as well, assuming there is
sufficient disk space, the following sequence may be used
instead
DBQ>
DBQ>
file
DBQ>
DBQ>
find all of <database>;
print; # To check if everything is O.K. before erasing
erase <database>
rename current <database>
>PA
SORT
SYNTAX
SORT database BY keyname1 {, keyname2} . . . ;
Details
old
- database is a database name
- keyname is the name of a field to sort on, optionally followed
by "ASC" (default) or "DESC".
- The sort order is major through minor (e.g. keynameN within
keynameN-1 . . . within keyname2 within keyname1).
- Records are sorted in situ. It takes a while for a large
database.
- It is not advisable to abort a sort halfway through - be
patient.
Example
sort accounts by name, balance desc;
>PA
Erase a database
ERASE
DBQ Command Reference
Syntax
ERASE database
Details
- database is the name of a database
The named database file is erased from the disk. It cannot be
recovered except by immediate use of a program such as UNERA.
This command is equivalent to the CPM ERA command, which can be
used as an alternative.
Example
DBQ> erase current
>PA
Rename database
RENAME
DBQ Command Reference
Syntax
RENAME olddatabase newdatabase
Details
- olddatabase is the existing name of a database
- newdatabase is the desired new name for the database
The use of this command results in the same action as use of the
CPM REN command, which can be used as an alternative.
Example
DBQ> find all of employees with dept = 300;
DBQ> rename current ourdept
>PA
Define procedure
DEFINE
DBQ Command Reference
Syntax
DEFINE procname
Details
- procname is the name of the procedure to be defined
DBQ prompts
empty line
definitions
effectively
you for the definition on subsequent lines.
An
is used to terminate the definition. As procedure
overwrite previous definitions, a null definition
deletes a procedure.
Procedures can be used for a wide range of purposes.
In its most simple form it can be used to set up synonyms for
the query language command keywords for a non-English language,
or for personal preference.
Also it can be used for the
following :To replace sequences of words with a single keyword.
To specify part of, or all, a complex query.
To specify a sequence of commands.
To specify a sequence of commands with variable parameters input
via the ENTER command (see ENTER command for details).
Procedures can be nested. That is, a procedure can refer to
another procedure within its definition. Procedures referring
to procedures referring back to the original will cause problems
when used, and must be avoided.
Example
DBQ> define total
DEFINE> print all+ of
DEFINE>
DBQ> total accounts;
>PA
Show procedure
DBQ Command Reference
SHOW
Syntax
SHOW procname
SHOW ;
Details
- procname is the name of the procedure to be listed
- if procname is replaced by a terminator or keyword, a list
currently defined procedures is shown.
Example
DBQ> show list
print all of
DBQ> show ;
of
list
DBQ>
Prompt for value
ENTER
DBQ Command Reference
Syntax
ENTER procname
ENTER "procname"
Details
- procname is an identifier
Causes a prompt to be issued for the identifier, and after
reading one line, sets the procedure to that value.
A null
entry deletes the procedure. This is used in command files, and
in other procedures, to prompt for input as part of a sequence
of commands. The procedure in this case is just a simple value,
but it is called in the same manner as a full multiline
procedure.
Where the procname is specified inside quotation marks, it
indicates that the definition should be contained
within
quotation marks. This is used when entering string literals for
comparison purposes.
Example
DBQ> define findemp
DEFINE> enter empno:
DEFINE> enter "name:"
DEFINE> print all of employees with empno = empno:
DEFINE> and name = name: ;
DEFINE>
DBQ> findemp
DBQ> Enter empno:
>PA
Set options
SET
Syntax
DBQ Command Reference
SET [NO] [FOLD] [VERIFY] [LOG] [PAGE];
Details
This permits
specified.
options
to
be
set,
or
unset if "NO" is first
The options are:NO
The word "NO" changes the sense of the setting to that
unset. Thus "SET NO FOLD;" would unset the fold option.
of
FOLD
Fold permits alphabetic case folding on comparisons.
e.g.
"FrEd" would match with "fReD"
VERIFY
Verify causes the contents of command files to be output during
execution. This may be used to check that the command file is
running correctly.
Comments should be inserted in the command
file to keep track of where you are.
LOG
Log causes a log file to be created, and all input from the
terminal to be written to it. Unsetting log simply switches off
the writing, and subsequent setting of the log simply switches
on the writing again.
When the "exit" command is issued, the file is closed and a
message output saying that it has been closed, prior to DBQ
finishing.
PAGE
Page allows pagination to be done on tabulations.
Simply
setting page will set a pagelength of 60 detail lines, correct
for 11 inch depth paper. Other page depths can be accomodated
by quoting the number of detail lines to be printed per page
after the set page command.
e.g.
set page 20
sets the pagelength at 20 detail lines.
If page in unset, an effective page length of 32000 is
and no page number will be printed.
set
up,
Pagination is effective on both normal print tabulations and on
format file driven output, for which a special value may again
be required depending on page layout.
Set display
After the options have been set or unset, the current settings
are displayed. Each option name is followed by a number.
For
FOLD, VERIFY and LOG, a value of 0 indicates unset, and 1
indicates set. For PAGE, the page length is displayed.
Example
set fold page 62 no verify ;
Fold = 1, verify = 0, log = 0, page = 62
>PA
Online help
HELP
Syntax
HELP
?
DBQ Command Reference
Details
This causes an initial page of help information to be output to
the terminal.
A prompt is then issued to press ^Z, ENTER, or a
character.
If ENTER is pressed, the next page of help is printed.
If ^Z is pressed, the program returns to the DBQ> prompt.
If a character is pressed, the next help page relating to a
topic starting with that character is displayed. If a character
is pressed which is not the initial of any remaining help frame,
DBQ returns to the DBQ> prompt.
Example
DBQ> help
--- page of help --Press ^Z to abort, ENTER to continue, or x for help on x...
c
--- page of help on "create" -->PA
Exit from DBQ
DBQ Command Reference
EXIT
Syntax
EXIT
Details
This returns you to the CPM+ prompt.
If a log file is currently open (although not necessarily being
written to), it is closed and a message to that effect is
displayed.
Example
DBQ> exit
A>
>PA
Command files
DBQ Command Reference
@
Syntax
@filename
Details
- filename is the full name of a file containing commands.
This causes the contents of the specified file to be inserted at
the current point in the input. The command file may contain
any input, apart from the response to an "enter" request.
If "verify" is set, the contents of the file are output
terminal as it is read.
to
the
If the file "DBQINIT.CMD" is present when DBQ is started, it is
executed initially, and can be used to set up procedure
definitions etc.
Comments can be inserted in a command file, or indeed in direct
input, by preceding them with "#". Everything on a line after a
"#" is ignored.
The ENTER command can be used to input variable data for use
within the command file, in a similar manner as within a
procedure.
Also, an ENTER command for a dummy variable can be
used to halt the command file execution until you respond to the
enter request. The dummy variable can be immediately used as a
command on the next line, and will allow you to enter "exit" to
exit from DBQ if there is a problem.
>PA
Database administration
MAINTENANCE
DBQ Usage notes
Introduction
To effectively control your databases, it is necessary to
beyond just setting them up and using them.
think
This section describes some requirements of proper database
administration and suggests ways of achieving these.
Setting up
A number of things can be done to make life easier when using
DBQ.
The DBQINIT.CMD file can be used to set up procedures to
be used either generally or against a specific database.
These
procedures may be simple abbreviations for database print
requests etc. or they can be larger sequences of commands to
enable interactive working against the database using the
"enter" command.
It is also possible, on the Amstrad CPC, to set up common
commands on the keypad.
A sample keypad definition file is
provided which can be used as the basis of a custom keypad
definition.
The CCP key configuration is useful also, as it
sets the cursor keys to support the CCP editing functions used
by DBQ.
Security
Security covers two aspects of data management. The first is
the protection of confidential information.
For
personal
computers this is not usually a problem, but if you do share a
machine with others, it is suggested that you keep confidential
databases on specific disks which you can put in a safe place.
The other aspect of security is insurance against data loss.
This can be achieved for most purposes by making regular backup
copies of your database disks. If you are planning on doing a
long session on a database, firstly copy the database to a
backup disk, then set the log option when you start the DBQ
session. If something goes wrong during the session, the log
file will contain the commands you entered and can be used as a
command file against a new copy of the database from the backup
(do not use the backup itself!). It is possible to edit the
command file to truncate the file at some known point.
It is
then possible to recover nearly up to the point at which things
went wrong.
Reformatting
It is possible to reformat the database in a number of ways.
When a FIND command is done, a CURRENT database is created which
can be renamed as a permanent database.
Thus fields can be
renamed or dropped, or data from more than one database can be
used to form a new one. If a new field is needed in a database,
it can be added by creating a temporary database with just one
record containing the new field or fields in it, with the
initial value, and joining this with the main database in a
select operation.
>PA
Database administration
MAINTENANCE
DBQ Usage notes
It is also possible to reformat a database by exporting the
records, creating a new database with the required format,
editing the data file and importing the datafile into the new
database. It may be useful to specify a format file to create
an output file already in the new format to be imported - e.g.
>field2<
>field1<
newfield value
>field3<
If this is used to PRINT the old database containing three
fields, the data can then be imported into the new database
containing four fields.
>PA
General notes
GENERAL
DBQ usage notes
General points
DBQ is designed to be simple to use, and reasonably foolproof.
There is no need to explicitly open or close databases, or to do
saves to the disk, as the database is opened and closed for each
operation. This means that when you are at the DBQ prompt,
there are no databases currently open, and it is safe to abort
the program using ^C, or by taking out the disk and switching
off the computer.
Query style
Whilst the query facility is very powerful, it is often not the
best approach to request a large complex selection at one go.
If you are using the query facility as a means of choosing from
the available records, it is better to firstly see how many
records a more general search will produce, and then add further
refinements until a suitable subset is found. For example, if
we have a database of cars containing information about all
current production cars, and we wish to select one to suit a
particular customer, we can reduce the selection on some
important criteria firstly, such as the price, and then select
from the resultant cars. For example:DBQ> find cars with price < 5000 and price > 2500;
DBQ> print current with doors = 4 and mpg > 40;
Making a log file
There are two ways of making a logfile of the interaction with
DBQ. The SET LOG option allows input to be logged, and the
resultant file can be used as a command file, either directly or
after being edited.
It is also possible to use the CPM+ 'put' transient to redirect
the console output to a file, for example by using the command
'put console to file conout.log'. This will permit a full log
of both input and output to be obtained.
Joining multiple databases
One of the properties relational databases is the ability to
join together the data from two or more databases, based on the
relationship between them. DBQ uses the power of the selection
expression to not only express the required relationship between
the databases, but also to select from the resultant data that
which meets selection criteria in the same manner as selection
from a single database. The relationship can be expressed not
only in terms of single field equivalence, but of multi-field
relationships.
For a simple multi-database join, a straightforward
on the related fields is all that is required.
comparison
DBQ>
print
parts.partno;
all
of
orders,
For a more complex join, the
further specification.
parts
required
with
order.partno
relationship
will
=
need
DBQ> print all of employees, depts with employees.dept >=
DBQ> depts.lowdept and employees.dept <= depts.highdept;
This joins the employees file with the department records for
which they are within the department number range.
For selections involving more than two databases, the extra
relations can be specified between any of the participating
databases. It is also possible to join a database with itself,
although this demands the use of a database name alias, and
appropriate qualification. Further details of this are provided
in the section on aliases.
Limitations
The various limits that DBQ has on data storage are as follows:Maximum size of any one database file - 64k bytes.
Maximum numeric field length (including sign
bytes.
and
Maximum number of decimal places - 10.
Maximum character field length - 128 characters.
Maximum number of fields in database - 30.
Maximum field name length - 10 characters.
Maximum database name length - 10 characters.
Maximum procedure name length - 10 characters.
point)
-
12
Maximum command line length - 128 bytes.
- Although a number of lines can make up a command.
As well as these limits, there is a limit on the amount of
dynamic memory that can be allocated for file buffers, etc.
This is quite high, and handles a fairly complex query against
three database files of 5 fields at the same time as using a
command file for input, a format file for output formatting,
output to a report file, with a current log file being produced,
and with about 2k to 3k of procedure definitions.
Details of
how to deal with a memory full error are contained in the
section on error messages.
>PA
Output formatting
REPORTS
DBQ usage notes
Report formatting
The PRINT command normally lists the records in tabular form.
Other formats are possible using the format file. The USING
option on the PRINT command can specify the name of a format
file (Default extension .FMT).
This format file contains the
text to be output, together with an indication of where the
fields are to be printed. In its simplest form, it contains the
field specifiers only, but it can also contain heading text and
a flag character to cause a pause at the terminal after each
record.
Field specifiers
Field specifiers come in two forms, as follows.
<fieldname>
and
>fieldname<
The first of these indicates that the field should be printed as
its full width.
For character fields, the field is left
justified with space fill to the right. For numeric fields, the
field is right justified with space fill to the left.
The second form indicates that the field should be printed in
minimum width form, whereby only the necessary characters are
printed, and no space fill occurs. This form is used for such
purposes as mailmerge where the surrounding text can be properly
concatenated with the field value.
Note that the field name used can be the normal field name, or
an alias if one has been specified. It is preferable to use
aliases if qualification is otherwise necessary due to the field
name not being unique to one database.
Heading specification
A percent sign "%" at the start of the file indicates that any
following text up to the next percent sign is heading text and
should only be output once at the start. Careful positioning of
the percent signs permits the correct spacing of the heading
lines.
The number of heading lines should be used when
calculating any page length setting.
When pagination is in effect (see the SET PAGE option), the
heading will be printed every time the specified number of
records have been printed.
Careful specification of the text
areas is necessary to achieve correct results from this, and
some experimentation is invariably necessary.
A number sign ("#") within the heading text will be replaced by
the current page number.
The number sign will also
be
recognized within the detail text, and permits the page number
to be output for each record if desired.
Pause specification
A question mark "?" at the end of the format file indicates
that the output should stop at this point before printing the
next record. The operator may then press ENTER to print the
next record, or ^Z to stop the printing.
This may be used for browsing through the file on the screen, or
for printing mail merge output onto single sheets of paper.
Uses of format files
The format file facilities provide a range of formatting
possibilities beyond the immediately obvious.
The following
list provides some suggestions, although these are by no means
all the possibilities.
Alternative tabulations, with differing heading styles with page
numbering at specified points. Single, double, triple or indeed
any line spacing. Unit specifiers for value fields (e.g. 25143
cwt, 96 cc, etc.).
Fields duplicated on same or different
lines.
Paged browsing, using nicely formatted screens containing the
fields in forms with fancy titles, side headings and borders.
Printout of database onto forms, again with headings etc.
Mail merge, using a letter produced on a word processor, with
field specifiers at appropriate points.
Formatting of data for input to a BASIC or other applications
program.
(e.g.
">string
field<",>numeric field<,constant
data,>another field<).
Formatting of data to permit reformatting of the database file
itself.
An example of this is given in the section on
reformatting.
Label printing, using a simple format file.
And of course the data used in these various formats of output
can come from selected fields from a complex selection from more
than one database.
>PA
Messages and Errors
MESSAGES
DBQ User manual
Introduction
The following list of messages describe the likely cause of each
error situation, and where applicable corrective action that may
be taken.
Informational messages
These messages are printed for your information, and do not
indicate that anything has gone wrong.
The following informational messages will appear.
DBQ.LOG closed
This is output when an EXIT command is issued, if the log
file has been opened using the SET LOG command. It is used
to remind you that the log file has been written, and that
you should either do something with the log file, or delete
it to free up the disk space occupied.
Fold = ?, verify = ?, log = ?, page = ??
This is output whenever a SET command is issued, to show the
resultant settings.
Press ENTER to continue, ^Z to quit, x for help on x...
This is output after each page of
HELP
information
displayed, and gives you the option of viewing the next help
page, quitting from the help display, or looking for the
next help topic starting with the given letter.
[ nnn records xxxxxx ]
Where xxxxxx can =
Freed.
Found,
Updated,
Inserted,
Deleted
or
This is output whenever a PRINT, FIND, UPDATE, INSERT,
DELETE or COMPRESS command is issued, and indicates the
number of records taking part in the operation.
Press ENTER to continue, ^Z to quit
This is output after each record is printed,
prompting character is specified in a format file.
if
the
nnnn swaps in nnnn passes
This is output after a sort operation completes, to indicate
how many record swaps took place.
A large number will
indicate that the file was not close to the sort order
requested.
>PA
Error messages
These messages indicate that the requested action could not be
performed as requested.
In certain cases a complete query may
have been recognized up to the point of a syntax error. In this
case, the query will have been actioned, but error will also be
reported.
These errors will be printed in the general form:### Error: error details ###
Where "error details" are specific error types, and will be one
of the following:syntax error
This is the most common message and indicates that DBQ did
not understand the command that you issued. Generally, this
means that you have typed a command name or other keyword
incorrectly, but can mean that the order of the words in the
command is incorrect, or that certain options are not
available on the command. It can also be caused by a string
literal not being enclosed in quotation marks.
If you are in doubt about what word the error was raised on,
try typing the command in one word to a line. As soon as an
error is detected, the message will be output. Whilst this
helps in the majority of cases, in some cases the actual
word or construct in error is earlier on in the query, and
is only brought to light when the command is terminated.
set parameter unknown
An incorrect option has been specified for the SET
Check the spelling of options in the SET command.
command.
memory full
This message indicates that the dynamic memory of the system
is full.
If this message is reported, steps can be taken to release
some memory, by deleting unwanted procedures, and by not
using a log file. It is recommended that an exit is made,
and DBQ restarted, without defining unwanted procedures, and
without starting a log file.
This will
remove
any
fragmented dynamic memory, and provide the maximum space to
run a query. If this still fails, the query will have to be
reduced in size or complexity.
It may help on a query against a number of databases to use
the FIND command to select the required data into a
temporary database as an intermediate step, and reduce the
overhead caused by having a number of databases open. Quite
often a little experimentation will cure the problem.
disk full
This indicates that the disk to which you are writing does
not have enough space to write a file. You should exit from
DBQ and tidy up the disk before proceeding.
database file not found
The database file that you specified does not exist. Either
you have mispelled the name of the database, or you are
using the wrong disk.
database name undefined
The database name specified in a selection expression has
not been used in the database name list of the command.
bad file header
The database file specified does not have a valid DBQ header
section. You may have renamed a non-DBQ file with the .DBQ
extension, or the database file may have been corrupted in
some manner. Restore the latest backup copy and bring the
database up to date. If you don't have a backup copy, read
the section on database administration, ready for the next
disk corruption.
creating database
An error has occurred whilst creating the database. This
may be due to the database name already being in use, or the
disk being write protected.
field name duplicated
When creating a database, a fieldname
than once.
has
been
used
more
field name ambiguous
Within a query, a field name has been used that appears in
more than one of the databases named.
In this case, the
name should be qualified by prefixing it with the database
name and a full stop.
expression too complex
A selection expression has been used that is too complex to
parse.
It is usually necessary to reduce the complexity.
It may be sufficient to specify the expression in a
different manner.
too many fields
Too many fields have been specified for a database, during a
CREATE operation.
reading record
An error occurred when reading a record.
the disk having been removed.
writing record
This may be due to
An error occurred when writing a record. This may be caused
by the disk being full, or by the disk being removed during
the command.
input file not found
The input file specified cannot be found on the disk.
creating output file
An error occurred whilst attempting to create the specified
output file.
This may be due to the file already existing,
or the disk being write protected.
command file not found
The specified command file could not be found on the disk.
Also the following error messages may appear as shown:### Maximum line length is 128 ###
Re-enter>
An input line longer than the allowed maximum has been
used.
To overcome this problem simply split the command up
and enter it on multiple lines.
### Out of memory using <procname> ###
Dynamic memory was exhausted when attempting to expand the
named procedure.
See the 'memory full' error for an
explanation of likely causes and suggested remedial action.
### Error opening ICF <filename> ###
An error occurred when
command file named.
attempting
to
open
the
indirect
### Procedure <procname> not found ###
A definition for the named procedure could not be found.
Sorry - help file not available.
The help file 'DBQ.HLP' is not present on the disk. You
will probably have removed it due to its size.
It is
possible to produce a reduced file with just the summary
details on it by editing the full file, after taking a
backup copy. You can add any useful information or personal
notes and hints at the end of the file.
Other error situations
Other occasions may arise where an erroneous situation can be
assumed to exist. Certain obscure combinations of circumstance
may, perhaps, result in the computer entering a "hard loop".
This situation is easy to detect, as it is impossible to break
out of the program by the usual means of pressing control-C, and
the disk drives may remain running but not doing anything. If
this is the case (and you have not pressed a combination of keys
which switches the printer output on when a printer is not
attached, which results in an error message being displayed by
CPM+ on the bottom line of the screen after a delay of around 20
to 30 seconds), it will be necessary to carefully shut the
computer down and reboot CPM.
>PA
>PA his
case, the query will have been