CASE 表示式

CASE  expr

      WHEN comparison_expr1 THEN return_expr1        

      WHEN comparison_expr2 THEN return_expr2         

      WHEN comparison_exprn THEN return_exprn         

  ELSE else_expr

END

用中文來說，case 、when 、else，

即 如果 條件1成立 ，那麼執行條件1，條件都不符合則執行else ，例如例，如果job_id='IT_PROG'，那麼將薪資*1.10

例：

SELECT last_name, job_id, salary,

       CASE job_id

                  WHEN 'IT_PROG'  THEN  1.10*salary

                   WHEN 'ST_CLERK' THEN  1.15*salary

                   WHEN 'SA_REP'   THEN  1.20*salary

       ELSE      salary

END    

"REVISED_SALARY"

FROM   hr.employees;      

//從emp表中返回 列名"REVISED_SALARY"，如果JOB_ID='ST_CLERK',則返回的值=1.15*salary，如果JOB_ID='SA_REP' ，則返回的值=1.20*salary，否則直接返回salary的值

[email protected]> SELECT last_name, job_id, salary,

  2         CASE job_id

  3                    WHEN 'IT_PROG'  THEN  1.10*salary

  4                     WHEN 'ST_CLERK' THEN  1.15*salary

  5                     WHEN 'SA_REP'   THEN  1.20*salary

  6         ELSE      salary

  7  END    

  8  "REVISED_SALARY"

  9  FROM   hr.employees;

LAST_NAME                 JOB_ID         SALARY REVISED_SALARY

------------------------- ---------- ---------- --------------

OConnell                  SH_CLERK         2600           2600

Grant                     SH_CLERK         2600           2600

Whalen                    AD_ASST          4400           4400

Hartstein                 MK_MAN          13000          13000

Fay                       MK_REP           6000           6000

Mavris                    HR_REP           6500           6500

Baer                      PR_REP          10000          10000

Higgins                   AC_MGR          12008          12008

Gietz                     AC_ACCOUNT       8300           8300

King                      AD_PRES         24000          24000

Kochhar                   AD_VP           17000          17000

De Haan                   AD_VP           17000          17000

Hunold                    IT_PROG          9000           9900

Ernst                     IT_PROG          6000           6600

Kaufling                  ST_MAN           7900           7900

Vollman                   ST_MAN           6500           6500

Mourgos                   ST_MAN           5800           5800

Landry                    ST_CLERK         2400           2760

Markle                    ST_CLERK         2200           2530

Bissot                    ST_CLERK         3300           3795

Atkinson                  ST_CLERK         2800           3220

Tucker                    SA_REP          10000          12000

Bernstein                 SA_REP           9500          11400

Hall                      SA_REP           9000          10800

Olsen                     SA_REP           8000           9600