Matakuliah
Tahun
: T0413
: 2009
Stored Procedure, UDF and Triggers
Pertemuan 9
Stored Procedures
Server
Client Application
SQL #1
SQL #2
SQL #3
Network
myproc
SQL #1
CALL myproc
SQL #2
SQL #3
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Stored Procedures
• Database objects that usually contain one or more SQL
statements as well as procedural (business) logic
• Executed and managed by DB2 (server-side objects)
• Can be written using SQL PL, C/C++, Java, Cobol, CLR
supported languages, and OLE
• Benefits for using stored procedures include:
– Centralized business logic that promotes code re-use
– Improved security
– Improved performance
• In this workshop, we focus on SQL PL procedures
because of their popularity, good performance and
simplicity
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IBM Data Studio
• Replaces the DB2 Developer Workbench of DB2 9
• Installed separately from DB2 9.5
• Based on Eclipse
Creating your first SQL PL Stored Procedure
 Using the Command Editor:
connect to sample
create procedure p1 begin end
 Using the IBM Data Studio
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Basic stored procedure structure
CREATE PROCEDURE proc_name [( {optional parameters}
)]
[optional procedure attributes]
<statement>
<statement> is a single statement, or a set of statements
grouped by BEGIN [ATOMIC] ... END
Optional stored procedure attributes
LANGUAGE SQL
RESULT SETS <n> (required if returning result sets)
SPECIFIC my_unique_name
ƒ can be same as procedure name
ƒ highly recommended for manageability:
–GRANT EXECUTE ON SPECIFIC PROCEDURE ...
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–DROP SPECIFIC PROCEDURE ...
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Parameters
CREATE PROCEDURE proc(IN p1 INT, OUT p2 INT, INOUT p3 INT)
...
IN - Input parameter
OUT - Output parameter
INOUT - Input and Output parameter
All params must be provided in CALL statement
Comments in SQL PL Stored Procedures
 -- This is an SQL-style comment
 /* This is a C-style coment */
(valid within SQL procedures )
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Compound statements
Compound
Statement
BEGIN [ATOMIC]
<declare variables>
<declare conditions>
<declare statements>
<declare cursors>
<declare handlers>
<logic >
END
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Optionally atomic
Declarations
Logic Can contain other
compound stmts
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Variable declaration
DECLARE var_name <data type> [ DEFAULT
value];
 Note: Default value is NULL
Examples:
DECLARE temp1 SMALLINT DEFAULT 0;
DECLARE temp2 INTEGER DEFAULT 10;
DECLARE temp3 DECIMAL(10,2) DEFAULT
100.10;
DECLARE temp4 REAL DEFAULT 10.1;
DECLARE temp5 DOUBLE DEFAULT 10000.1001;
DECLARE temp6 BIGINT DEFAULT 10000;
DECLARE temp7 CHAR(10) DEFAULT 'yes';
DECLARE temp8 VARCHAR(10) DEFAULT 'hello';
DECLARE temp9 DATE DEFAULT '1998-12-25';
DECLARE temp10 TIME DEFAULT '1:50 PM';
DECLARE temp11 TIMESTAMP DEFAULT '200101-05-12.00.00';
DECLARE
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University temp12 CLOB(2G);
DECLARE temp13 BLOB(2G);
Assignment
statements
 SET total = 100;
ƒ Same as VALUES(100) INTO total;
 SET total = NULL;
ƒ any variable can be set to NULL
 SET total = (select sum(c1) from T1);
ƒ Condition is raised if more than one row
 SET first_val = (select c1 from T1 fetch first
1 row only)
ƒ fetch only the first row from a table
 SET sch = CURRENT SCHEMA;
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Example: Stored procedure with parameters
CREATE PROCEDURE P2 ( IN
v_p1 INT,
INOUT v_p2 INT,
OUT
v_p3 INT)
LANGUAGE SQL
SPECIFIC myP2
BEGIN
-- my second SQL procedure
SET v_p2 = v_p2 + v_p1;
SET v_p3 = v_p1;
END
To call the procedure from the Command Editor: call P2 (3, 4, ?)
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Cursors
Cursor declaration and usage:
DECLARE <cursor name> CURSOR [WITH RETURN <return target>] FOR
<SELECT statement>;
OPEN <cursor name>;
FETCH <cursor name> INTO <variables>
CLOSE <cursor name>;
The <return target> value can be to “CLIENT or CALLER”
ƒ CLIENT: result set will be returned to the client application
ƒ CALLER: result set will be returned to the client or stored procedure that made
the call
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Example: Stored procedure returning result sets
CREATE PROCEDURE set ()
DYNAMIC RESULT SETS 1
LANGUAGE SQL
BEGIN
DECLARE cur CURSOR WITH RETURN TO CLIENT
FOR SELECT name, dept, job
FROM staff
WHERE salary > 20000;
OPEN cur;
END
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Example: Processing a cursor
CREATE PROCEDURE sum_salaries(OUT sum INTEGER)
LANGUAGE SQL
BEGIN
DECLARE p_sum INTEGER;
DECLARE p_sal INTEGER;
DECLARE c CURSOR FOR
SELECT SALARY FROM EMPLOYEE;
DECLARE SQLSTATE CHAR(5) DEFAULT '00000';
SET p_sum = 0;
OPEN c;
FETCH FROM c INTO p_sal;
WHILE(SQLSTATE = '00000') DO
SET p_sum = p_sum + p_sal;
FETCH FROM c INTO p_sal;
END WHILE;
CLOSE c;
SET sum = p_sum;
END
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SQLCODE and SQLSTATE
Access requires explicit declaration:
DECLARE SQLSTATE CHAR(5);
DECLARE SQLCODE INT;
Can be declared ONLY at outermost scope and
automatically set by DB2 after each operation
SQLCODE
= 0, successful.
> 0, successful with warning
< 0, unsuccessful
= 100, no data was found.
i.e. FETCH statement returned no
data
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SQLSTATE
Success: SQLSTATE
'00000'
Not found: SQLSTATE
'02000'
Warning: SQLSTATE
'01XXX'
Exception: Everything else
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Conditions
A condition represents a given SQLSTATE
It can be raised by any SQL statement
You can provide names to a condition to make your code more readable
Built-in names for general conditions:
SQLWARNING, SQLEXCEPTION, NOT FOUND
These map to the SQLSTATEs mentioned in the previous slide
Specific conditions:
SQLSTATE '01004‘
To assign a user-defined name to a condition:
DECLARE truncation CONDITION FOR SQLSTATE '01004'
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Condition Handling
A condition handler must specify
• handled conditions
• where to resume execution (CONTINUE, EXIT or UNDO)
• action to perform to handle the condition
Action can be any statement (including control structures)
Upon SQLEXCEPTION condition,if no handler exists, the procedure
terminates and returns to the client with error
raises
exception
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BEGIN [ATOMIC]
DECLARE <type> HANDLER FOR <conditions>
<handler-action>
statement_1;
CONTINUE point
statement_2;
statement_3;
END
UNDO or EXIT point
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Flow control statements
CASE (selects an execution path (simple / searched))
IF
FOR (executes body for each row of table)
WHILE
ITERATE (forces next iteration. Similar to CONTINUE in C)
LEAVE (leaves a block or loop. "Structured Goto")
LOOP (infinite loop)
REPEAT
GOTO
RETURN
CALL (procedure call)
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Dynamic SQL
Useful when the final form of SQL is known only at RUN TIME
Example: if col1 and tabname are variables:
'SELECT ' || col1 || ' FROM ' || tabname;
Also recommended for DDL to avoid dependency problems and
package invalidation, and to implement recursion.
Keywords:
ƒ EXECUTE IMMEDATE - ideal for single execution SQL
ƒ PREPARE + EXECUTE - ideal for multiple execution SQL
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Example: Dynamic SQL
prerequisite: create table T2 (c1 int, c2 int)
CREATE PROCEDURE dyn1 (IN value1 INT, IN value2 INT)
SPECIFIC dyn1
BEGIN
DECLARE stmt varchar(255);
DECLARE st STATEMENT;
SET stmt = 'insert into T2 values (?, ?)';
Compile stmt once
PREPARE st FROM stmt;
Execute it many times
EXECUTE st USING value1, value1;
EXECUTE st USING value2, value2;
SET stmt = 'insert into T2 values (9,9)';
EXECUTE IMMEDIATE stmt;
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END
Compile and execute once
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Calling from CLI
SQLCHAR *stmt = (SQLCHAR *)
SQLDOUBLE sal = 20000.0;
SQLINTEGER salind = 0;
"CALL MEDIAN_RESULT_SET( ? )" ;
/* Bound to parameter marker in stmt */
/* Indicator variable for sal */
sqlrc = SQLPrepare(hstmt, stmt, SQL_NTS);
sqlrc = SQLBindParameter(hstmt, 1, SQL_PARAM_OUTPUT,
SQL_C_DOUBLE, SQL_DOUBLE, 0, 0, &sal, 0, &salind);
SQLExecute(hstmt);
if (salind == SQL_NULL_DATA)
printf("Median Salary = NULL\n");
else
printf("Median Salary = %.2f\n\n", sal );
sqlrc = StmtResultPrint(hstmt);
sqlrc = SQLMoreResults(hstmt);
/* Get first result set */
/* Check for another result set */
if (sqlrc == SQL_SUCCESS) {
/* There is another result set */
sqlrc = StmtResultPrint(hstmt);
}
See sqllib/samples/sqlproc/rsultset.c
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Calling Stored Procedures from a VB.NET Application
Try
‘ Create a DB2Command to run the stored procedure
Dim procName As String = “TRUNC_DEMO”
Dim cmd As DB2Command = conn.CreateCommand()
Dim parm As DB2Parameter
cmd.CommandType = CommandType.StoredProcedure
cmd.CommandText = procName
‘ Register the
parm
parm.Direction
parm
parm.Direction
output parameters for the DB2Command
= cmd.Parameters.Add(“v_lastname”, DB2Type.VarChar)
= ParameterDirection.Output
= cmd.Parameters.Add(“v_msg”, DB2Type.VarChar)
= ParameterDirection.Output
‘ Call the stored procedure
Dim reader As DB2DataReader = cmd.ExecuteReader
Catch myException As DB2Exception
DB2ExceptionHandler(myException)
Catch
UnhandledExceptionHandler()
End
Try
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Calling Stored Procedures from a Java Application
try
{
// Connect to sample database
String url = “jdbc:db2:sample”;
con = DriverManager.getConnection(url);
CallableStatement cs = con.prepareCall(“CALL trunc_demo(?,
?)”);
// register the output parameters
callStmt.registerOutParameter(1, Types.VARCHAR);
callStmt.registerOutParameter(2, Types.VARCHAR);
cs.execute();
con.close();
}
catch (Exception e)
{
/* exception handling logic goes here */
}
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User Defined Function
Inline SQL PL
SQL PL = SQL Procedural Language
Inline SQL PL
This is a SQL PL subset supported within a dynamic SQL
statement, triggers and UDFs
Dynamic compound SQL
It means using a BEGIN ATOMIC – END block. The “ATOMIC”
part, makes the entire compound SQL be treated as a single
UOW (unit of work)
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Example: Randomly populating a table
Pre-req:
create sequence myseq@
create table T1 (id bigint, data char(100), insert_ts timestamp)@
Inline SQL PL:
begin atomic
declare cnt INT default 0;
while (cnt < 20000) do
insert into t1 values (
nextval for MYSEQ,
(select case
when (rand() < 0.5) then null
else space(int(rand()*100))
end case from sysibm.sysdummy1),
current timestamp);
set cnt=cnt+1;
end while;
end
@
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User-Defined Functions
• Functions always return a value
• Some built-in functions already exist out-of-the-box
– Eg: SUM(), AVG(), DIGITS(), etc.
• Can create UDFs in:
– SQL PL, C/C++, Java, CLR (Common Language
Runtime), and OLE (Object Linking and
Embedding)
– In this workshop, we focus on SQL PL functions
because of their simplicity and popularity
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Types of functions
• Scalar functions
– Return a single value
– Cannot change database state (i.e. no INSERT, UPDATE,
DELETE statements allowed)
– Example: COALESCE( ), SUBSTR( )
• Table functions
– Return values in a table format
– Called in the FROM clause of a query
– Can change database state (i.e. allow INSERT, UPDATE,
DELETE statements)
– Example: SNAPSHOT_DYN_SQL( ), MQREADALL( )
• Others type of functions (not covered in this
course):
– Row functions
– Column functions
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Scalar function
 Scalar functions take input values and return a single value
They cannot be used to modify table data
Example:
CREATE FUNCTION deptname(p_empid VARCHAR(6))
RETURNS VARCHAR(30)
SPECIFIC deptname
BEGIN ATOMIC
DECLARE v_department_name VARCHAR(30);
DECLARE v_err VARCHAR(70);
SET v_department_name = (
SELECT d.deptname FROM department d, employee e
WHERE e.workdept=d.deptno AND e.empno= p_empid);
SET v_err = 'Error: employee ' || p_empid || ' was not found';
IF v_department_name IS NULL THEN
SIGNAL SQLSTATE '80000' SET MESSAGE_TEXT=v_err;
END IF;
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RETURN v_department_name;
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END
Invoking Scalar UDFs
• Scalar UDFs can be invoked in SQL statements
wherever a scalar value is expected, or in a
VALUES clause
– SELECT DEPTNAME(‘000010’) FROM
SYSIBM.SYSDUMMY1
– VALUES DEPTNAME(‘000010’)
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Table UDFs
• Return a table of rows
• Used in the FROM clause of a query
• Similar to a view, except more powerful because data
modification statements (INSERT/UPDATE/DELETE)
can be performed
• Typically used to return a table and keep an audit record
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Table function example
 A function which enumerates a set of employees of a department
CREATE FUNCTION getEnumEmployee(p_dept VARCHAR(3))
RETURNS TABLE
(empno CHAR(6),
lastname VARCHAR(15),
firstnme VARCHAR(12))
SPECIFIC getEnumEmployee
RETURN
SELECT e.empno, e.lastname, e.firstnme
FROM employee e
WHERE e.workdept=p_dept
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Calling a Table function
Used in the FROM clause of an SQL statement
The TABLE() function must be applied and must be aliased.
SELECT * FROM
TABLE (getEnumEmployee('E01')) T
TABLE() function
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alias
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Triggers
• A trigger is a database object defined on a
table and fired when an INSERT, UPDATE,
or DELETE operation is performed.
• Activate (“fire”) automatically
• Operations that cause triggers to fire are
called triggering SQL statements
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Types of Triggers
• BEFORE
– activation before row is inserted, updated or deleted
– Operations performed by this trigger cannot activate other triggers
(i.e. INSERT, UPDATE, and DELETE operations are not permitted)
• AFTER
– Activated after the triggering SQL statement has executed to
successful completion
– May activate other triggers (cascading permitted up to 16 levels)
• INSTEAD OF
– Defined on views
– Logic defined in the trigger is executed instead of the triggering SQL
statement
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A Simple BEFORE Trigger
define
qualifier for
new values
if no value
provided on
insert, column is
NULL
CREATE TRIGGER default_class_end
NO CASCADE BEFORE INSERT ON cl_sched
REFERENCING NEW AS n
FOR EACH ROW
MODE DB2SQL
WHEN (n.ending IS NULL)
SET n.ending = n.starting + 1 HOUR
optional
WHEN
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A Simple INSTEAD OF Trigger
• It is activated when performing changes to a view
• Prereq:
CREATE TABLE countries (id int, country varchar(50), region varchar (50),
average_temp int)
CREATE VIEW view1 (id, continent, temperature) as
SELECT id, region, average_temp from countries
CREATE TRIGGER update_view1
INSTEAD OF UPDATE ON view1
REFERENCING OLD AS o NEW AS n
FOR EACH ROW
MODE DB2SQL
BEGIN ATOMIC
UPDATE countries
SET region = n.region
WHERE region = o.region;
END
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