流程控制
講解條件語句,循環語句。
本次環境會用到表emp;下面是emp執行語句。

drop table emp; create table EMP( EMPNO numeric(4) not null, ENAME varchar(10), JOB varchar(9), MGR numeric(4), HIREDATE date, SAL numeric(7 ), COMM numeric(7 ), DEPTNO numeric(2)); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7369, 'SMITH', 'CLERK', 7902, to_date('1980-12-17', 'YYYY-MM-DD'), 800, null, 20); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7499, 'ALLEN', 'SALESMAN', 7698, to_date('1981-02-20', 'YYYY-MM-DD'), 1600, 300, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7521, 'WARD', 'SALESMAN', 7698, to_date('1981-02-22', 'YYYY-MM-DD'), 1250, 500, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7566, 'JONES', 'MANAGER', 7839, to_date('1981-04-02', 'YYYY-MM-DD'), 2975, null, 20); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7654, 'MARTIN', 'SALESMAN', 7698, to_date('1981-09-28', 'YYYY-MM-DD'), 1250, 1400, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7698, 'BLAKE', 'MANAGER', 7839, to_date('1981-05-01', 'YYYY-MM-DD'), 2850, null, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7782, 'CLARK', 'MANAGER', 7839, to_date('1981-06-09', 'YYYY-MM-DD'), 2450, null, 10); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7788, 'SCOTT', 'ANALYST', 7566, to_date('1987-04-19', 'YYYY-MM-DD'), 3000, null, 20); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7839, 'KING', 'PRESIDENT', null, to_date('1981-11-17', 'YYYY-MM-DD'), 5000, null, 10); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7844, 'TURNER', 'SALESMAN', 7698, to_date('1981-09-08', 'YYYY-MM-DD'), 1500, 0, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7876, 'ADAMS', 'CLERK', 7788, to_date('1987-05-23', 'YYYY-MM-DD'), 1100, null, 20); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7900, 'JAMES', 'CLERK', 7698, to_date('1981-12-03', 'YYYY-MM-DD'), 950, null, 30); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7902, 'FORD', 'ANALYST', 7566,to_date('1981-12-02', 'YYYY-MM-DD'), 3000, null, 20); insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) values (7934, 'MILLER', 'CLERK', 7782, to_date('1982-01-23', 'YYYY-MM-DD'), 1300, null, 10);
1. 條件語句
IF和CASE語句讓你可以根據某種條件執行命令。
PL/pgSQL有三種形式的IF:
IF ... THEN ... END IF; IF ... THEN ... ELSE ... END IF; IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF;
以及兩種形式的CASE:
CASE ... WHEN ... THEN ... ELSE ... END CASE; CASE WHEN ... THEN ... ELSE ... END CASE;
1.1 IF條件語句
語法結構:
IF search_condition THEN statement_list END IF; ----------------------- IF search_condition THEN statement_list ELSE statement_list END IF; ----------------------- IF search_condition THEN statement_list ELSIF search_condition THEN statement_list ELSE statement_list END IF;
案例1:給員工薪水少於1500元提示“多加工資”;反之。
CREATE OR REPLACE FUNCTION if_test(vc_empno NUMERIC) RETURNS void AS $$ DECLARE vn_sal numeric; BEGIN select sal into vn_sal from emp where empno = vc_empno; IF vn_sal is null THEN RAISE NOTICE '該員工不存在!'; ELSIF vn_sal < 1500 THEN RAISE NOTICE '老板;請多加點工資'; ELSE RAISE NOTICE '老板;請少加點工資'; END IF; END; $$ LANGUAGE PLPGSQL;
調用測試
lottu=# SELECT if_test(7399); NOTICE: 該員工不存在! lottu=# SELECT if_test(7369); NOTICE: 老板;請多加點工資 lottu=# SELECT if_test(7566); NOTICE: 老板;請少加點工資
1.2 CASE條件語句
--
CREATE OR REPLACE FUNCTION case_test1(x NUMERIC) RETURNS void AS $$ DECLARE msg text; BEGIN CASE x WHEN 1, 2 THEN msg := 'one or two'; ELSE msg := 'other value than one or two'; END CASE; RAISE NOTICE 'look it, it is %' ,msg; END; $$ LANGUAGE PLPGSQL; CREATE OR REPLACE FUNCTION case_test2(x NUMERIC) RETURNS void AS $$ DECLARE msg text; BEGIN -- msg := CASE WHEN x in (1,2) THEN 'one or two' ELSE 'other value than one or two' END; CASE WHEN x in (1,2) THEN msg := ''one or two''; ELSE msg := 'other value than one or two'; END CASE; RAISE NOTICE 'look it, it is %' ,msg; END; $$ LANGUAGE PLPGSQL;
2.循環
2.1 簡單循環
[ <<label>> ] LOOP statements EXIT [ label ] [ WHEN boolean-expression ]; END LOOP [ label ];
- LOOP定義一個無條件的循環,無限循環,直到由EXIT或RETURN語句終止。
- 可選的label可以由EXIT和CONTINUE語句使用,用於在嵌套循環中聲明應該應用於哪一層循環。
- 如果聲明了WHEN,循環退出只有在boolean-expression為真的時候才發生, 否則控制會落到EXIT后面的語句上。
案例1:輸出一個1-10的列表
CREATE OR REPLACE FUNCTION LOOP_TEST_01() RETURNS void AS $$ DECLARE n numeric := 0; BEGIN LOOP n := n + 1; RAISE NOTICE 'n 的當前值為: %',n; EXIT WHEN n >= 10; END LOOP; END; $$ LANGUAGE PLPGSQL;
2.2 WHILE 循環
語法:
WHILE boolean-expression LOOP statements; END LOOP;
只要條件表達式(boolean-expression)為真,WHILE語句就會不停的在一系列語句上進行循環, 條件是在每次進入循環體的時候檢查的。
CREATE OR REPLACE FUNCTION LOOP_TEST_02() RETURNS void AS $$ DECLARE n numeric := 0; BEGIN WHILE n < 10 LOOP n := n + 1; RAISE NOTICE 'n 的當前值為: %',n; END LOOP; END; $$ LANGUAGE PLPGSQL;
2.3. FOR (integer variant)
語法:
FOR name IN [ REVERSE ] expression .. expression [ BY expression ] LOOP statements END LOOP [ label ];
每循環一次,循環變量自動加1;使用關鍵字REVERSE,循環變量自動減1。跟在IN REVERSE 后面的數字必須是從小到大的順序,而且必須是整數,不能是變量或表達式。可以使用EXIT 退出循環。
FOR i IN 1..10 LOOP -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop END LOOP; FOR i IN REVERSE 10..1 LOOP -- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop END LOOP; FOR i IN REVERSE 10..1 BY 2 LOOP -- i will take on the values 10,8,6,4,2 within the loop END LOOP;
2.4 for遍歷命令結果
語法:
FOR target IN query LOOP statements END LOOP [ label ];
這種在實際工作過程中;由於需要用到游標,經常用它來替換游標。
在這里注意到是:i變量必須要聲明為RECORD; 這在oracle的存儲過程沒這個設置。
CREATE OR REPLACE FUNCTION LOOP_TEST_03() RETURNS void AS $$ DECLARE i RECORD; BEGIN FOR i IN select ename,job from emp where deptno = 20 loop RAISE NOTICE '% job is %', i.ename ,i.job; end loop; END; $$ LANGUAGE PLPGSQL;
2.5 CONTINUE語句
語法:
CONTINUE [ label ] [ WHEN boolean-expression ];
CONTINUE可以用於所有類型的循環;它並不僅僅限於無條件循環,不會跳出循環。
CREATE OR REPLACE FUNCTION LOOP_TEST_04() RETURNS void AS $$ DECLARE n numeric := 0; BEGIN WHILE n < 10 LOOP n := n + 1; CONTINUE WHEN n = 5; RAISE NOTICE 'n 的當前值為: %',n; END LOOP; END; $$ LANGUAGE PLPGSQL;
2.6 EXIT語句
語法:
EXIT [ label ] [ WHEN boolean-expression ];
EXIT可以用於在所有的循環類型中,它並不僅僅限制於在無條件循環中使用。 會跳出循環。
CREATE OR REPLACE FUNCTION LOOP_TEST_05() RETURNS void AS $$ DECLARE n numeric := 0; BEGIN WHILE n < 10 LOOP n := n + 1; EXIT WHEN n = 5; RAISE NOTICE 'n 的當前值為: %',n; END LOOP; END; $$ LANGUAGE PLPGSQL;