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Tahun
Versi
: <<M0094>>/<<Pengantar Sistem Basis Data>>
: <<2005>>
: <<1/1>>
Pertemuan 13
Programatic SQL
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Mahasiswa dapat Menunjukkan
pemakaian instruksi programatic SQL
2
Outline Materi
• SQL embedded pada high level language
• perbedaan static dan dinamic embeded
SQL
• static embedded SQL
• dinamic embedded SQL
3
Appendix E
Programmatic SQL
Transparencies
4
Chapter 21 - Objectives
 How
SQL statements can be embedded in highlevel programming languages.
 Difference
between static and dynamic
embedded SQL.
 How to write programs that use static
embedded SQL.
 How to write programs that use dynamic
embedded SQL.
 How to use the Open Database Connectivity
(ODBC) de facto standard.
5
Embedded SQL
 SQL
can be embedded in high-level procedural
language.
 In many cases, language is identical although
SELECT statement differs.
 Two types of programmatic SQL:
– Embedded SQL statements.
» SQL supports Ada, C, COBOL, FORTRAN,
MUMPS, Pascal, and PL/1.
– Application program interface (API).
6
Example 21.1 - CREATE TABLE
EXEC SQL CREATE TABLE Viewing (
propertyNo VARCHAR2(5) NOT NULL,
clientNo VARCHAR2(5) NOT NULL,
viewDate DATE NOT NULL,
comment VARCHAR2(40));
if (sqlca.sqlcode >= 0)
printf(“Creation successful\n”);
7
Embedded SQL
 Embedded
SQL starts with identifier, usually
EXEC SQL [ ‘@SQL(’ in MUMPS].
 Ends
with terminator dependent on host
language:
– Ada, ‘C’, and PL/1: terminator is semicolon (;)
– COBOL: terminator is END-EXEC
– Fortran: ends when no more continuation lines.
 Embedded SQL can appear anywhere an
executable host language statement can appear.
8
SQL Communications Area (SQLCA)
 Used
to report runtime errors to the
application program.
 Most important part is SQLCODE variable:
0 - statement executed successfully;
< 0 - an error occurred;
> 0 - statement executed successfully, but an
exception occurred, such as no more rows
returned by SELECT.
9
SQLCA for Oracle
10
WHENEVER Statement
 Every
embedded SQL statement can potentially
generate an error.
 WHENEVER is directive to precompiler to
generate code to handle errors after every SQL
statement:
EXEC SQL WHENEVER
<condition>
<action>
11
WHENEVER Statement
 condition
can be:
SQLERROR - generate code to handle errors
(SQLCODE < 0).
SQLWARNING - generate code to handle warnings.
NOT FOUND - generate code to handle specific warning
that a retrieval operation has found no more records.
12
WHENEVER Statement

action can be:
CONTINUE - ignore condition and proceed to next
statement.
DO - transfer control to an error handling function.
DO BREAK - place an actual “break” statement in the
program.
DO CONTINUE - place an actual “continue” statement
in the program.
GOTO label or GO TO label - transfer control to
specified label.
STOP - rollback all uncommitted work and terminate the
program.
13
WHENEVER Statement
EXEC SQL WHENEVER SQLERROR GOTO error1;
EXEC SQL INSERT INTO Viewing VALUES (‘CR76’,
‘PA14’, ‘12-May-2001’, ‘Not enough space’);
 would
be converted to:
EXEC SQL INSERT INTO Viewing VALUES (‘CR76’,
‘PA14’, ‘12-May-2001’, ‘Not enough space’);
if (sqlca.sqlcode < 0) goto error1;
14
Host Language Variables
 Program
variable declared in host language.
 Used in embedded SQL to transfer data from
database into program and vice versa.
 Can be used anywhere a constant can appear.
 Cannot be used to represent database objects,
such as table names or column names.
 To use host variable, prefix it by a colon (:).
15
Host Language Variables
EXEC SQL UPDATE Staff
SET salary = salary + :increment
WHERE staffNo = ‘SL21’;
 Need to declare host language variables to SQL,
as well as to host language:
EXEC SQL BEGIN DECLARE SECTION;
float increment;
EXEC SQL END DECLARE SECTION;
16
Indicator Variables

Indicates presence of null:
0 associated host variable contains valid value.
<0 associated host variable should be assumed to
contain a null; actual contents of host variable
irrelevant.
>0 associated host variable contains valid value.

Used immediately following associated host
variable with a colon (:) separating two variables.
17
Indicator Variables - Example
EXEC SQL BEGIN DECLARE SECTION;
char address[51];
short addressInd;
EXEC SQL END DECLARE SECTION;
addressInd = -1;
EXEC SQL UPDATE PrivateOwner
SET address = :address :addressInd
WHERE ownerNo = ‘CO21’;
18
Singleton SELECT - Retrieves Single Row
EXEC SQL SELECT fName, lName, address
INTO :firstName, :lastName, :address :addressInd
FROM PrivateOwner
WHERE ownerNo = ‘CO21’;
Must be 1:1 correspondence between expressions
in SELECT list and host variables in INTO clause.
 If successful, SQLCODE set to 0; if there are no
rows that satisfies WHERE, SQLCODE set to
NOT FOUND.

19
Cursors
 If
query can return arbitrary number of rows,
need to use cursors.
 Cursor allows host language to access rows of
query one at a time.
 Cursor acts as a pointer to a row of query result.
Cursor can be advanced by one to access next row.
 Cursor must be declared and opened before it can
be used and it must be closed to deactivate it after
it is no longer required.
20
Cursors - DECLARE CURSOR
 Once
opened, rows of query result can be
retrieved one at a time using FETCH:
EXEC SQL DECLARE
propertyCursor CURSOR FOR
SELECT propertyNo, street, city
FROM PropertyForRent
WHERE staffNo = ‘SL41’;
21
Cursors - OPEN
 OPEN
statement opens specified cursor and
positions it before first row of query result:
EXEC SQL OPEN propertyCursor;
22
Cursors - FETCH and CLOSE
 FETCH
retrieves next row of query result table:
EXEC SQL FETCH propertyCursor
INTO :propertyNo, :street, :city

FETCH is usually placed in a loop. When there are
no more rows to be returned, SQLCODE is set to
NOT FOUND.
EXEC SQL CLOSE propertyCursor;
23
ISO Standard for Embedded SQL
 Standard
does not recognize SQLWARNING of
WHENEVER statement.
 Standard does not mention an SQLCA. It does,
however,
recognize
the
integer variable
SQLCODE, although this is a deprecated feature
that is supported only for compatibility with
earlier versions of the standard.
 Instead, defines a character string SQLSTATE
parameter, comprising a two-character class code
followed by a three-character subclass code.
24
ISO Standard for Embedded SQL
 Standard
specifies definition and processing of
cursors slightly differently from that presented
above. ISO DECLARE CURSOR is:
EXEC SQL DECLARE cursorName
[INSENSITIVE] [SCROLL]
CURSOR FOR selectStatement
[FOR {READ ONLY |
UPDATE [OF columnNameList]}]
25
ISO Standard for Embedded SQL
 FETCH
statement:
EXEC SQL FETCH [[fetchOrientation] FROM]
cursorName INTO hostVariable [, . . . ]

fetchOrientation can be one of:
–
–
–
–
–
–
NEXT
PRIOR
FIRST
LAST
ABSOLUTE
RELATIVE
26
Dynamic Embedded SQL
 With
static embedded SQL, cannot use host
variables where database object names required.
 Dynamic SQL allows this.
 Idea is to place complete SQL statement in a host
variable, which is passed to DBMS to be executed.
 If SQL statements do not involve multi-row
queries, use EXECUTE IMMEDIATE statement:
EXEC SQL EXECUTE IMMEDIATE
[hostVariable | stringLiteral]
27
Dynamic Embedded SQL
For example:
sprintf(buffer, “UPDATE Staff
SET salary = salary + %f
WHERE staffNo = ‘SL21’ ”, increment);
EXEC SQL EXECUTE IMMEDIATE :buffer;
28
PREPARE and EXECUTE
 DBMS
must parse, validate, and optimize each
EXECUTE IMMEDIATE statement, build
execution plan, and execute plan.
 OK if SQL statement is only executed once in
program; otherwise inefficient.
 Dynamic SQL provides alternative: PREPARE
and EXECUTE.
 PREPARE tells DBMS to ready dynamically built
statement for later execution.
29
PREPARE and EXECUTE
 Prepared
statement assigned name. When
statement is subsequently executed, program need
only specify this name:
EXEC SQL PREPARE statementName
FROM [hostVariable | stringLiteral]
EXEC SQL EXECUTE statementName
[ USING hostVariable [indicatorVariable] [, ...] |
USING DESCRIPTOR descriptorName ]
30
Parameter Markers
USING allows portions of prepared statement to
be unspecified, replaced by placeholders
(parameter markers).
 Placeholder can appear anywhere in hostVariable
or stringLiteral of PREPARE that constant can
appear.
 Tells DBMS value will be supplied later, in
EXECUTE statement.

31
Placeholders
sprintf(buffer, “UPDATE Staff
SET salary = :sal
WHERE staffNo = :sn”);
EXEC SQL PREPARE stmt FROM :buffer;
EXEC SQL EXECUTE stmt
USING :newSalary, :staffNo;

sal and sn are placeholders.
32
Static versus Dynamic SQL
33
SQL Descriptor Area (SQLDA)
 Alternative
way to pass parameters to EXECUTE
statement is through SQLDA.
 Used when number of parameters and their data
types unknown when statement formulated.
 SQLDA can also be used to dynamically retrieve
data when do not know number of columns to be
retrieved or the types of the columns.
34
SQLDA for Oracle
35
SQL Descriptor Area (SQLDA)
 Two
SQL statements to set up and access SQLDA:
DESCRIBE BIND VARIABLES (host variables
also known as bind variables) fills in an SQLDA
for any bind variables specified in the query.
DESCRIBE SELECT LIST fills in an SQLDA for
column data when wish to dynamically retrieve
data and number of columns to be retrieved or
types of the columns are not known.
36
Fields in SQLDA
N field: maximum number of placeholders or
SELECT list columns that can be described.
Set by application. After DESCRIBE, N and F fields are
set to actual number of elements.
F field: actual number of placeholders or SELECT
list columns found by DESCRIBE.
37
Fields in SQLDA
V field: pointer to array of addresses to data buffers
that store the input host variables or SELECT list
columns. Set by application.
For placeholders, data buffers must be allocated and
array set prior to OPEN; for SELECT list columns,
data buffers must be allocated and array set prior to
first FETCH.
38
Fields in SQLDA
L field: pointer to array of lengths of input host
variables or SELECT list columns.
For placeholders, lengths must be set prior to OPEN;
for SELECT list columns, DESCRIBE sets maximum
length for each column value, which can be modified.
T field: pointer to array of data type codes for input
host variables or SELECT list columns.
39
Fields in SQLDA
I field: pointer to array of addresses of buffers that
store indicator variable values.
For placeholders, these values must be set prior to
OPEN; for SELECT list columns, must be set prior to
FETCH.
S field: pointer to array of addresses of data buffers
to store placeholder names or SELECT list names.
Buffers are allocated and their addresses stored in S by
SQLSQLDAAlloc(). DESCRIBE stores the names in
these buffers.
40
Fields in SQLDA
M field: pointer to array of maximum lengths of data
buffers to store placeholder names or SELECT list
names.
Set by Oracle SQLSQLDAAlloc() function.
C field: pointer to array of current lengths of
placeholder names or SELECT list names.
Set by DESCRIBE.
41
Fields in SQLDA
X field: pointer to array of addresses of data buffers
to store indicator variable names. This field applies
only to placeholders.
Buffers are allocated and their addresses stored in X by
SQLSQLDAAlloc(). DESCRIBE stores the names in
these buffers.
Y field: pointer to array of maximum lengths of data
buffers to store indicator variable names. Again, this
field applies only to placeholders.
Set by SQLSQLDAAlloc().
42
Fields in SQLDA
Z field: pointer to array of current lengths of
indicator variable names. As with X and Y, this field
applies only to placeholders.
Set by DESCRIBE.
43
DESCRIBE
 Returns
names, data types, and lengths of columns/
placeholders specified in query into an SQLDA.
 For non-select, sets F field to 0.
EXEC SQL DESCRIBE BIND VARIABLES FOR
statementName INTO bindDescriptorName
EXEC SQL DESCRIBE SELECT LIST FOR
statementName INTO selectDescriptorName
 statementName
is name of prepared statement and
DescriptorNames are names of initialized SQLDAs.
44
DESCRIBE
sprintf(query, “SELECT propertyNo, rent
FROM PropertyForRent”);
EXEC SQL PREPARE stmt FROM :query;
EXEC SQL DESCRIBE SELECT LIST FOR
stmt INTO sqlda;

sqlda will be filled in as shown overleaf.
45
DESCRIBE – Completed SQLDA
46
Retrieving Data Using Dynamic SQL

Again, use cursors to retrieve data from a query
result table that has an arbitrary number of rows.
EXEC SQL DECLARE cursorName
CURSOR FOR selectStatement
EXEC SQL OPEN cursorName [FOR READONLY]
{USING hostVariable [indicatorVariable] [,...] |
USING DESCRIPTOR descriptorName }
EXEC SQL FETCH cursorName
{INTO hostVariable [indicatorVariable] [,...] |
USING DESCRIPTOR descriptorName }
EXEC SQL CLOSE cursorName
47
Retrieving Data Using Dynamic SQL
 OPEN
allows values for placeholders to be
substituted using one or more hostVariables in:
– USING clause or
– passing values via descriptorName (SQLDA) in
a USING DESCRIPTOR clause.
 Main difference is with FETCH, which now uses
descriptorName to receive rows of query result
table (or one or more hostVariables/
indicatorVariables).
48
Retrieving Data Using Dynamic SQL
 Before
FETCH, program must provide data
areas to receive retrieved data and indicator
variables.
 Basic steps for dynamic SQL statement are:
(1) Declare host string in DECLARE SECTION to hold text
of the query.
(2) Declare a select SQLDA and, if required, a bind SQLDA.
(3) Allocate storage space for the SQLDA(s).
(4) Set maximum number of columns in select SQLDA and,
if query can have placeholders, maximum number of
placeholders in bind SQLDA.
49
Retrieving Data Using Dynamic SQL
(5) Put the query text into the host string.
(6) PREPARE the query from the host string.
(7) DECLARE a cursor for the query.
(8) If the query can have placeholders:
(a) DESCRIBE bind variables into bind SQLDA.
(b) Reset number of placeholders to number actually
found by DESCRIBE.
(c) Get values and allocate storage space for bind
variables found by DESCRIBE.
(9) OPEN cursor USING the bind SQLDA, or if no bind
SQLDA has been used, USING the select SQLDA.
50
Retrieving Data Using Dynamic SQL
(10) DESCRIBE the column list INTO the select SQLDA.
(11) Reset number of column list items to number actually
found by DESCRIBE.
(12) Reset length and data type of each column list item.
(13) FETCH each row from database into allocated data
buffers pointed to by the select SQLDA and process it,
as appropriate.
(14) Deallocate the storage space used for the column list
items, placeholders, indicator variables, and SQLDAs.
(15) CLOSE the cursor.
51
ISO Standard for Dynamic SQL
The SQLDA in the ISO standard is treated like a
variable of an ADT. Programmer has access only
to the SQLDA using set of methods.
 An SQLDA is allocated and deallocated using
statements:

ALLOCATE DESCRIPTOR descriptorName
[WITH MAX occurrences]
DEALLOCATE DESCRIPTOR descriptorName
52
ISO Standard for Dynamic SQL

The SQLDA can be accessed using:
GET DESCRIPTOR descriptorName {hostVariable = COUNT
| VALUE itemNumber hostVariable1 = itemName1 [, …] }
SET DESCRIPTOR descriptorName {COUNT = hostVariable
| VALUE itemNumber itemName1 = hostVariable1 [, …] }

Some common ISO descriptor names are:
–
–
–
–
TYPE: data type of item;
LENGTH: length of data in the item;
INDICATOR: associated indicator value;
DATA: the data value.
53
ISO Standard for Dynamic SQL

For example, to get maximum number of
allocated elements of the descriptor, count, say:
EXEC SQL GET DESCRIPTOR :sqlda :count = COUNT;
 To
set up first element of descriptor:
EXEC SQL SET DESCRIPTOR :sqlda
VALUE 1 INDICATOR –1 DATA :data
54
ISO Standard for Dynamic SQL
Standard also provides two DESCRIBE
statements to distinguish between description of
input and output parameters.
 DESCRIBE
INPUT
statement
provides
description of input parameters (placeholders) for
a prepared statement.
 DESCRIBE OUTPUT provides description of
resultant columns of dynamic SELECT
statement.
 In both cases, format is similar to DESCRIBE
statements used above.

55
Open Database Connectivity (ODBC)
With an API, rather than embedding raw SQL
within program, DBMS vendor provides API.
 API consists of set of library functions for many
common types of database accesses.
 One problem with this approach has been lack of
interoperability.
 To standardize this approach, Microsoft produced
ODBC standard.
 ODBC provides common interface for accessing
heterogeneous SQL databases, based on SQL.

56
Open Database Connectivity (ODBC)
(built on ‘C’) provides high degree of
interoperability: single application can access
different SQL DBMSs through common code.
 Enables developer to build and distribute c-s
application without targeting specific DBMS.
 Database drivers are then added to link
application to user’s choice of DBMS.
 ODBC has emerged as a de facto industry
standard.
 Interface
57
ODBC’s Flexibility
Applications not tied to proprietary vendor API.
 SQL statements can be explicitly included in
source code or constructed dynamically.
 An application can ignore underlying data
communications protocols.
 Data can be sent and received in format that is
convenient to application.
 Design aligned with X/Open and ISO CLI.
 There are ODBC drivers available today for many
of most popular DBMSs.

58
ODBC Interface
 Library
of functions that allow application to
connect to DBMS, execute SQL statements, and
retrieve results.
 A standard way to connect and log on to a DBMS.
 A standard representation of data types.
 A standard set of error codes.
 SQL syntax based on the X/Open and ISO CallLevel Interface (CLI) specifications.
59
ODBC Architecture
 ODBC
architecture has four components:
– Application,
– Driver Manager,
– Driver and Database Agent,
– Data Source.
60
ODBC Architecture
Application - performs processing and calls ODBC
functions to submit SQL statements to DBMS and
to retrieve results from DBMS.
Driver Manager - loads drivers on behalf of
application. Driver Manager, provided by Microsoft,
is Dynamic-Link Library (DLL).
61
ODBC Architecture
Driver and Database Agent - process ODBC
function calls, submit SQL requests to specific
data source, and return results to application.



If necessary, driver modifies application’s request
so that it conforms to syntax supported by
associated DBMS.
With multiple drivers, these tasks performed by the
driver; no database agent exists.
With single driver, agent designed for each
associated DBMS and runs on database server side.
62
ODBC Architecture
Data Source - consists of data user wants to access
and its associated DBMS, and its host operating
system, and network platform, if any.
63
ODBC Architecture
64
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