Lecture 4
PL/SQL language
PL/SQL language
• PL/SQL – procedural SQL
• Allows combining procedural and SQL code
• PL/SQL code is compiled, including SQL
commands
• PL/SQL code is executed:
• on the server (procedures, packages, triggers)
• can be executed on the client (e.g. Oracle
Forms applications)
Example Java code
Connection conn = getDbConnection();
PreparedStatement pstm;
Pstm = conn.prepareStatement(
"DELETE FROM some_table WHERE ID = ?");
pstm.setInt(1, 100);
pstm.executeUpdate();
• SQL code is:
• included as text
• interpreted at run-time
Example PL/SQL procedure
CREATE PROCEDURE update_salary(val number)
IS
BEGIN
FOR e IN (SELECT * FROM emp) LOOP
IF e.hire_date + 60 < SYSDATE THEN
UPDATE emp SET salary = salary + val
WHERE id = e.id;
END IF;
END LOOP;
COMMIT;
END;
Trigger definition example
CREATE OR REPLACE TRIGGER emp_id_trg
BEFORE INSERT ON emp
FOR EACH ROW
BEGIN
IF :new.id IS NULL THEN
SELECT emp_seq.NEXTVAL INTO :new.id
FROM DUAL;
END IF;
END;
Function definition example
CREATE OR REPLACE FUNCTION
count_rows RETURN NUMBER
IS
cnt NUMBER;
BEGIN
SELECT count(*) INTO cnt FROM some_table;
RETURN cnt;
END;
PL/SQL blocks
[DECLARE
var1
INTEGER;
var2
VARCHAR2(10000); ]
BEGIN
...
[EXCEPTION
-- exception handlers]
END;
PL/SQL language
• PL/SQL language is case insensitive (as well as
SQL in Oracle)
DECLARE
var1
INTEGER;
BEGIN
VAR1 := 3;
-- the following two statements
-- are identical
SELECT count(*) INTO var1 FROM tab1;
select COUNT(*) into VAR1 FROM TAB1;
END;
Variables
• Variables are defined in PASCAL convention:
name of the variable, then type
• Variable types:
• all SQL types and more:
• VARCHAR2 up to VARCHAR2(32767)
• BINARY_INTEGER
• PLS_INTEGER
• BOOLEAN
Assignments
• := operator is used for PL/SQL assignments
• in SQL UPDATE statement normal = is used:
DECLARE
i NUMBER;
BEGIN
i := 0;
UPDATE some_table t SET
t.col = i
where t.id = i;
END;
Assignments
• Functions and procedures are treated differently
• Function returns result, which must be used
CREATE FUNCTION f1 RETURN NUMBER ...;
DECLARE
res NUMBER;
BEGIN
f1;
-- incorrect
res := f1;
-- correct
SELECT f1 INTO res FROM DUAL; -- correct
END;
PL/SQL
• Operators
•=,<=, >=, != (comparisons)
•:= assignments
•LIKE, IN can be used in PL/SQL
• -- starts one line comment (like // in C++)
• /* multi line comment, like in C */
Conditional statements
IF condition THEN
statements;
END IF;
IF condition THEN
statements;
ELSIF condition THEN
statements;
ELSE
statements;
END IF;
Conditional statements
CASE expression
WHEN value1 THEN
statement;
WHEN value2 THEN
statement;
ELSE
statement;
END CASE;
Simple loop
LOOP
statement;
IF ... THEN
EXIT; -- exit loop
END IF;
statement
-- or
EXIT WHEN condition;
END LOOP;
WHILE loop
WHILE condition LOOP
...
/* statements */
...
END LOOP;
WHILE condition LOOP
...
EXIT WHEN condition;
...
END LOOP;
FOR loop
FOR i IN 1..10 LOOP
/* will execute 10 times */
....
END LOOP;
FOR i IN REVERSE 1..10 LOOP
-- starts from 10
-- will execute 10 times
...
END LOOP;
SQL statements in PL/SQL
• SELECT, UPDATE, INSERT, DELETE
statements can be used directly in PL/SQL
• UPDATE, INSERT, DELETE can be used as in
SQLPlus
• SELECT statement returns results:
• SELECT INTO can be used for statements
that return one row
• FOR loop can be used to iterate through the
results
• CURSOR can be used to fetch SELECT
statement results
SQL statements in PL/SQL
• SELECT, UPDATE, INSERT, DELETE
statements can be used directly in PL/SQL
– UPDATE, INSERT, DELETE can be used as in
SQLPlus
– SELECT statement returns results:
• SELECT INTO can be used for statements
that return one row
• FOR loop can be used to iterate through the
results
• CURSOR can be used to fetch SELECT
statement results
SQL statements in PL/SQL
• COMMIT, ROLLBACK, SAVEPOINT can be
used in PL/SQL
• DDL statements cannot be used in PL/SQL
directly
• PL/SQL variables can be used in SQL statements:
DECLARE
cnt NUMBER;
BEGIN
SELECT count(*) INTO cnt FROM table1;
UPDATE table2 SET
col1 = cnt WHERE id = 3;
END;
SQL statements in PL/SQL
• Oracle compiles PL/SQL code.
• Tables used in PL/SQL statements must exist
when the code is compiled
• Table, column names are fixed when the code
is compiled. It is not possible to use dynamic
table name like that:
DECLARE
tab_name VARCHAR2(30) := 'TABLE1';
BEGIN
UPDATE tab_name SET col1 = 0; -- error
SQL statements in PL/SQL
• In the following statement:
UPDATE tab1 SET value = value1
• tab1 is a name of existing database table, to
which current user must have access to. If the
table does not exist, compilation error is reported
• value is a name of a column in table tab1
• value1 can be a name of PL/SQL variable or
name of a column in table tab1
Illegal PL/SQL code
• The following code is illegal
CREATE FUNCTION count_rows
(table_name IN VARCHAR2)
RETURN NUMBER
IS
cnt NUMBER;
BEGIN
SELECT count(*) INTO cnt
FROM table_name;
RETURN cnt;
END;
SELECT statement in PL/SQL
• SELECT INTO:
SELECT x, y, z INTO var1, var2, var3 FROM ...;
• x, y, z are table column names
• var1, var2, var3 are PL/SQL variables
• Statement must return exactly one row:
• when no rows are returned NO_DATA_FOUND
exception is thrown
• when more than one row is returned
TOO_MANY_ROWS exception is thrown
SELECT statement in PL/SQL
• SELECT INTO example:
BEGIN
BEGIN
SELECT col1 INTO val1 FROM table1;
EXCEPTION
WHEN NO_DATA_FOUND THEN
val1 := NULL;
END;
...
END;
SELECT statement in PL/SQL
FOR rec IN (SELECT * FROM TABLE1) LOOP
IF rec.id > 100 THEN
EXIT;
END IF;
END LOOP;
• SQL statement must be in brackets
• FOR LOOP variable is of type record. It has all
the columns from the SELECT statement
• The loop is executed for each row returned from
the SELECT statement
• SELECT statement can return any number of
rows (also 0)
CURSORS
DECLARE
CURSOR c1 IS SELECT ename, job
FROM emp WHERE sal < 3000;
...
BEGIN
OPEN c1;
FETCH c1 INTO var1, var2;
IF c1%NOTFOUND THEN
...
END IF;
CLOSE c1;
END;
CURSOR with parameter
DECLARE
CURSOR c1(v NUMBER) IS SELECT ename, job
FROM emp WHERE sal < v;
value1 NUMBER;
BEGIN
OPEN c1(value1);
LOOP
FETCH c1 INTO var1, var2;
EXIT WHEN c1%NOTFOUND;
END LOOP;
CLOSE c1;
END;
CURSOR for loop
DECLARE
CURSOR c1(v NUMBER) IS SELECT ename, job
FROM emp WHERE sal < v;
BEGIN
FOR c1_rec in c1(10) LOOP
...
END LOOP;
END;
Anonymous blocks
[DECLARE
-- variable declarations]
BEGIN
-- statements
END;
• Anonymous blocks can be used
• in SQLPlus
• in Java and other languages
• as sub-block of larger PL/SQL block
• DECLARE part is optional, must be used if
variables are declared in anonymous block
Anonymous block example
SQLPLUS=>
BEGIN
FOR i IN 1 .. 1000 LOOP
INSERT INTO tab1 VALUES(i);
END LOOP;
END;
/
Note:
• "/" at the end is not part of the PL/SQL
language, it is just a signal to PL/SQL that
block code is finished and should be executed.
Anonymous block example
Connection conn = getDbConnection();
PreparedStatement pstm=conn.prepareStatement(
"BEGIN proc1; END;");
pstm.executeUpdate();
-- executes procedure proc1
Note:
• There is no "/" at the end of a block called from
Java or other languages
Anonymous sub-block
• Anonymous blocks:
...
-- large PL/SQL block
IF condition THEN
DECLARE
local_variable ...;
BEGIN
statements;
END;
END IF;
... -- large block continues
Procedures
• Procedure (as in Pascal) – function without result
CREATE PROCEDURE procedureName
(param1 IN
NUMBER,
param2
INTEGER, -- default is IN
param3 IN OUT VARCHAR2,
param4
OUT DATE) IS
localVar
INTEGER;
localVar1 VARCHAR2(100);
BEGIN
statements;
END;
/
Procedures
• Local variable declarations follow after IS
without DECLARE keyword
• The procedure ends with the "END;"
• The final "/" is used to signal to SQLPlus that the
function body is finished. After the "/" SQLPlus
will create the procedure
Parameter types
• Parameter types are IN, IN OUT and OUT:
• IN – caller passes input parameter to the
procedure. Parameter value can be changed in
the procedure, but caller will not see these
changes
• IN OUT – input/output parameter, caller will see
changes to parameter value
• OUT – output parameter, value is returned to the
caller
• Default parameter type is IN
Default parameter values
• Procedure and function parameters can have
default values
• Parameter with default value does not have to be
specified by the caller:
CREATE PROCEDURE proc(
p1 IN NUMBER DEFAULT 0) IS BEGIN
...
END;
/
BEGIN
proc(1); -- p1 = 1
proc;
-- p1 = 0
Passing parameters
• Parameters can be passed using three methods:
• positional – parameters are specified in the
same order as they are declared in the procedure:
proc1(1, 2, 'text value');
• named – parameter name is specified along
with its value.
proc1(p1 => 1, p2 => 2, p3 => 'text value');
• mixed – first parameters using positional
notation, the remaining using named notation:
proc1(1, p3 => 'text value');
Functions
CREATE FUNCTION functionName
(param1 IN
NUMBER)
RETURN VARCHAR2 IS
localVar
INTEGER;
localVar1 VARCHAR2(100);
BEGIN
statements;
RETURN localVar1;
END;
/