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 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 LOOP /* will execute 10 times */.... END LOOP; FOR i IN REVERSE LOOP -- starts from 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 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 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 END;

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; /