PL/SQL flow control statement

PL/SQL flow control statement

This blog introduces PL/SQL flow control statements, including the following three types
 Control statements: IF statement
 Loop statements: LOOP statement, EXIT statement
 Sequence statements: GOTO statement, NULL statement

A conditional statement

(1) Grammar

① 
IF<布尔表达式 > THEN
	PL/SQL和 SQL 语句
END IF;
②
IF<布尔表达式 > THEN
	PL/SQL和 SQL 语句
ELSE
	其它语句
END IF;
③
IF<布尔表达式 > THEN
	PL/SQL和 SQL 语句
ELSIF
< 其它布尔表达式 > THEN
其它语句
ELSIF< 其它布尔表达式 > THEN
	其它语句
ELSE
	其它语句
END IF;
注意：ELSIF别写错

(2) The case is as follows:

DECLARE
	v_empno emp.empno%TYPE;
	V_salary emp.sal%TYPE;
	V_comment VARCHAR2(35);
BEGIN
	SELECT sal INTO v_salary FROM emp WHERE empno=v_empno;
	IF v_salary<1500 THEN
		V_comment:= ‘ Fairly less’;
	ELSIF v_salary <3000 THEN
		V_comment:= ‘A little more’;
	ELSE
		V_comment:= ‘Lots of salary’;
	END IF;
	DBMS_OUTPUT.PUT_LINE(V_comment);
END;

Two case expressions

(1) Grammar

CASE selector
	WHEN expression1 THEN result1
	WHEN expression2 TH EN result2
	WHEN expressionN THEN resultN
	[ ELSE resultN+1]
END

(2) Case

DECLARE
	V_grade char(1)
	V_appraisal VARCHAR2(20);
BEGIN
	V_appraisal :=
	CASE v_grade
		WHEN ‘A’ THEN ‘Excellent’
		WHEN ‘B’ THEN ‘Very Good’
		WHEN ‘C’ THEN ‘Good’
		ELSE ‘No suc h grade’
	END;
	DBMS_OUTPUT.PUT_LINE(‘Grade:‘||v_grade||’ Appraisal: ‘|| 				   							v_appraisal);
END;

Three cycles

(1) Simple loop,
you can use exit to exit the loop

LOOP
	要执行的语句
	EXIT WHEN <条件语句>;/*条件满足，退出循环语句*/
END LOOP;

The case is as follows:

DECLARE
	int NUMBER(2) :=0;
BEGIN
	LOOP
		int := int + 1;
		DBMS_OUTPUT.PUT_LINE('int 的当前值为 :'||int);
		EXIT WHEN int =10;
	END LOOP;
END;

(2) While loop
Syntax:

WHILE<布尔表达式 > LOOP
	要执行的语句
END LOOP;

Case:

DECLARE
	x NUMBER :=1;
BEGIN
	WHILE x<=10 LOOP
		DBMS_OUTPUT.PUT_LINE('X 的当前值为 x);
		x:= x+1;
	END LOOP;
END;

(3) Digital loop
Syntax:
each loop, loop variable automatically increases by 1; using the keyword REVERSE, loop variable automatically decreases by 1. The numbers following IN REVERSE must be in ascending order, and must be integers, not variables or expressions. You can use EXIT to exit the loop.

FOR 循环计数器 IN [REVERSE ] 下限 .. 上限 LOOP
	要执行的语句
END LOOP;

Case:

BEGIN
	FOR int in 1..10 LOOP
		DBMS_ OUTPUT.PUT_LINE('int 的当前值为 : '||int);
	END LOOP;
END;

(4) The label and GOTO end the loop.
Syntax:

GOTO label;
. . . . .
<<label>>/*标号是用 括起来的标识符*/

Case study

DECLARE
	V_counter NUMBER := 1;
BEGIN
	LOOP
		DBMS_OUTPUT.PUT_LINE('V_counter 的当前值为 :'||V_counter);
		V_counter := v_counter + 1;
		IF v_counter > 10 THEN
			GOTO l_ENDofLOOP;--跳转标识
		END IF;
	END LOOP;
	<<l_ENDofLOOP>>
		DBMS_OUTPUT.PUT_LINE('V_counter 的当前值为 :'||V_counter);
END ;

(5) NULL statement
In a PL/SQL program, a null statement can be used to illustrate the meaning of not having to do anything, which is equivalent to a placeholder, which can make certain statements meaningful and improve the readability of the program.

DECLARE
	. . .
BEGIN
	…
	IF v_num IS NULL THEN
		GOTO print1;
	END IF;
	…
	<<print1>>
	NULL;--不需要处理任何数据。
END;