Download Data Definition Commands

Advanced SQL
Complex Queries, Joining
Tables
Some Basic SQL Numeric Functions
FUNCTION
OUTPUT
COUNT
The number of rows containing the specified attribute.
MIN
The minimum attribute value encountered.
MAX
The maximum attribute value encountered.
AVG
The arithmetic mean (average) for the specified attribute.
SUM
The sum of all values for a selected attribute.
COUNT
Example Aggregate
Function Operations
SELECT COUNT(DISTINCT V_CODE)
FROM PRODUCT;
SELECT COUNT(DISTINCT V_CODE)
FROM PRODUCT
WHERE P_PRICE <= 10.00;
MAX and MIN
SELECT MIN(P_PRICE)
FROM PRODUCT;
SELECT P_CODE, P_DESCRIPT, P_PRICE
FROM PRODUCT
WHERE P_PRICE = (SELECT MAX(P_PRICE) FROM
PRODUCT);
More Complex Queries and
SQL Functions
SUM
SELECT SUM(P_ONHAND*P_PRICE)
FROM PRODUCT;
AVG
SELECT P_DESCRIPT, P_ONHAND, P_PRICE,
V_CODE
FROM PRODUCT
WHERE P_PRICE >
(SELECT AVG(P_PRICE) FROM PRODUCT)
ORDER BY P_PRICE DESC;
More Complex Queries and
SQL Functions (con’t.)
Grouping data
– Creates frequency distributions
– Only valid when used with SQL arithmetic functions
SELECT P_SALECODE, MIN(P_PRICE)
FROM PRODUCT
GROUP BY P_SALECODE;
– HAVING clause operates like WHERE for grouping output
SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE)
FROM PRODUCT
GROUP BY V_CODE
HAVING AVG(P_PRICE) < 10;
More Complex Queries and
SQL Functions
Virtual tables: creating a view
– CREATE VIEW command
– Creates logical table existing only in virtual memory
CREATE VIEW PRODUCT_3 AS
SELECT P_DESCRIPT, P_ONHAND, P_PRICE
FROM PRODUCT
WHERE P_PRICE > 50.00;
SQL indexes: used to improve the efficiency of
data searches
CREATE INDEX P_CODEX
ON PRODUCT(P_CODE);
- Oracle automatically creates indexes on
primary keys
Complex Queries
Joining Database Tables
SELECT PRODUCT.P_DESCRIPT,
PRODUCT.P_PRICE, VENDOR.V_NAME,
VENDOR.V_CONTACT, VENDOR.V_AREACODE,
VENDOR.V_PHONE
FROM PRODUCT, VENDOR
WHERE PRODUCT.V_CODE = VENDOR.V_CODE;
The Results of a JOIN
Using Prefixes when Joining
Tables
Most current-generation DBMS, such as Oracle, do not
require the table name to be used as prefixes, unless the
same attribute name occurs in more then 1 table being
joined.
– If the product number was defined as p_prodnum in the product
table and v_prodnum in the vendor table, the table name need
not be specified when referenced
If the same attribute name occurs in several places, its
origin(table) must be specified
– Product.prod_num and Vendor.prod_num
Complex Queries
SELECT P_DESCRIPT, P_PRICE, V_NAME,
V_CONTACT, V_AREACODE, V_PHONE
FROM PRODUCT, VENDOR
WHERE PRODUCT.V_CODE =
VENDOR.V_CODE
AND P_INDATE > ‘08/15/1999’;
Natural Joins
Old style:
SELECT P_PRODUCT, V_VENDOR
FROM PRODUCT, VENDOR
WHERE PRODUCT.V_CODE = VENDOR.V_CODE
New style:
SELECT P_PRODUCT, V_VENDOR
FROM PRODUCT NATURAL JOIN VENDOR
Updatable Views
Views that can be updated which will
update their corresponding tables.
Views can be updatable if the primary key
of the base table is a column in the view
that also has unique values
Complete Lab #6 – Functions, Complex Queries, Views, Joining Tables
Sequences
Sequences are independent objects in the
database
They are considered “Auto-numbers”
They are created and used as primary
keys in tables where the key is a
sequential number
CREATE SEQUENCE Part_Num_Seq START WITH 100
Sequences on Insert
Refer to the sequence (auto-number)
object in place of the value needed for the
key when inserting data into a table
Can be used with NEXTVAL (sequence is
incremented) or CURRVAL (current value of
sequence is used)
INSERT INTO PARTS VALUES ( PART_ID_SEQ.NEXTVAL,
‘PART_NAME, ect……..)
Procedural SQL
Shortcomings of SQL
– SQL doesn’t support execution of a stored set of
procedures based on some logical condition.
– SQL fails to support the looping operations.
Solutions
– Embedded SQL
Embedded SQL can be called from within the
procedural programming language
– Shared Code
Critical code is isolated and shared by all application
programs.
Procedural SQL
Procedural SQL
– Procedural SQL allows the use of
procedural code and SQL statements that
are stored within the database.
– The procedural code is executed by the
DBMS when it is invoked by the end user.
– End users can use procedural SQL
(PL/SQL) to create:
Triggers
Stored procedures
PL/SQL functions
Procedural SQL
Triggers
– A trigger is procedural SQL code that is
automatically invoked by the RDBMS upon the
occurrence of a data manipulation event.
A trigger is always invoked before or after a
data row is selected, inserted, or updated.
A trigger is always associated with a database
table.
Each database table may have one or more
triggers.
A trigger is executed as part of the transaction
that triggered it.
Procedural SQL
– Role of triggers
Triggers can be used to enforce constraints
that cannot be enforced at the design and
implementation levels.
Triggers add functionality by automating
critical actions and providing appropriate
warnings and suggestions for remedial action.
Triggers can be used to update table values,
insert records in tables, and call other stored
procedures.
Triggers add processing power to the RDBMS
and to the database system.
Procedural SQL
Stored Procedures
– A stored procedure is a named collection of procedural and SQL
statements.
– Stored procedures are stored in the database and invoked by
name.
– Stored procedures are executed as a unit.
– The use of stored procedures reduces network traffic, thus
improving performance.
PL/SQL Stored Functions
Stored Functions
– is a named group of procedural and SQL statements that returns a
value.
– Invoked from within stored procedures or triggers
– Cannot be invoked from within SQL statements