Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL...

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Lecture 4 PL/SQL language

Transcript of Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL...

Page 1: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Lecture 4

PL/SQL language

Page 2: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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)

Page 3: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Example Java codeConnection 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

Page 4: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Example PL/SQL procedureCREATE 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;

Page 5: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Trigger definition exampleCREATE 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;

Page 6: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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;

Page 7: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

PL/SQL blocks

[DECLARE

var1 INTEGER;

var2 VARCHAR2(10000); ]

BEGIN

...

[EXCEPTION

-- exception handlers]

END;

Page 8: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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;

Page 9: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 10: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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;

Page 11: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Assignments• Functions and procedures are treated differently• Function returns result, which must be usedCREATE FUNCTION f1 RETURN NUMBER ...;

DECLARE

res NUMBER;

BEGIN

f1; -- incorrect

res := f1; -- correct

SELECT f1 INTO res FROM DUAL; -- correct

END;

Page 12: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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 */

Page 13: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Conditional statementsIF condition THEN

statements;

END IF;

IF condition THEN

statements;

ELSIF condition THEN

statements;

ELSE

statements;

END IF;

Page 14: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Conditional statementsCASE expression

WHEN value1 THEN

statement;

WHEN value2 THEN

statement;

ELSE

statement;

END CASE;

Page 15: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Simple loopLOOP

statement;

IF ... THEN

EXIT; -- exit loop

END IF;

statement

-- or

EXIT WHEN condition;

END LOOP;

Page 16: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

WHILE loopWHILE condition LOOP

...

/* statements */

...

END LOOP;

WHILE condition LOOP

...

EXIT WHEN condition;

...

END LOOP;

Page 17: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

FOR loopFOR 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;

Page 18: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 19: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 20: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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;

Page 21: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 22: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 23: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Illegal PL/SQL code• The following code is illegalCREATE FUNCTION count_rows

(table_name IN VARCHAR2)

RETURN NUMBER

IS

cnt NUMBER;

BEGIN

SELECT count(*) INTO cnt

FROM table_name;

RETURN cnt;

END;

Page 24: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 25: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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;

Page 26: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

SELECT statement in PL/SQLFOR 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)

Page 27: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

CURSORSDECLARE

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;

Page 28: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

CURSOR with parameterDECLARE

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;

Page 29: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

CURSOR for loopDECLARE

CURSOR c1(v NUMBER) IS SELECT ename, job

FROM emp WHERE sal < v;

BEGIN

FOR c1_rec in c1(10) LOOP

...

END LOOP;

END;

Page 30: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 31: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Anonymous block exampleSQLPLUS=>

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.

Page 32: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Anonymous block exampleConnection 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

Page 33: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Anonymous sub-block• Anonymous blocks:... -- large PL/SQL block

IF condition THEN

DECLARE

local_variable ...;

BEGIN

statements;

END;

END IF;

... -- large block continues

Page 34: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

Procedures• Procedure (as in Pascal) – function without resultCREATE 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;

/

Page 35: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 36: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

Page 37: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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

END;

Page 38: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

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');

Page 39: Lecture 4 PL/SQL language. PL/SQL – procedural SQL Allows combining procedural and SQL code PL/SQL code is compiled, including SQL commands PL/SQL code.

FunctionsCREATE FUNCTION functionName

(param1 IN NUMBER)

RETURN VARCHAR2 IS

localVar INTEGER;

localVar1 VARCHAR2(100);

BEGIN

statements;

RETURN localVar1;

END;

/