个回答

• 慕粉3810876

  2017-10-31 20:51:39

  已采纳

  case从严格意义上讲是if选择语句，是多条if语句的缩写形式，本质是属于条件判断，和循环流程控制不是一个概念
  

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• 慕粉4303271

  2017-10-31 20:47:33

  语法：

  CASE selector 

  WHEN exp1 then res1

  WHEN exp2 then res2

  WHEN exp3 then res3

  ...

  [ELSE resN]

  end;

  SQL> declare
  2 mygrade char(1):='A';
  3 res varchar2(20);
  4 begin
  5 res :=
  6 CASE mygrade
  7 WHEN 'A' THEN 'The mark is 90-100'
  8 WHEN 'B' THEN 'The mark is 80-90'
  9 WHEN 'C' THEN 'The mark is 70-80'
  10 WHEN 'D' THEN 'The mark is 60-70'
  11 WHEN 'E' THEN 'The mark is 0-60'
  12 END;
  13 dbms_output.put_line(res);
  14 end;
  15 /
  The mark is 90-100

  PL/SQL procedure successfully completed.

  SQL> 2
  2* mygrade char(1):='A';

  SQL> ch /'A'/'F'/
  2* mygrade char(1):='F';
  SQL> l 
  1 declare
  2 mygrade char(1):='F';
  3 res varchar2(20);
  4 begin
  5 res :=
  6 CASE mygrade
  7 WHEN 'A' THEN 'The mark is 90-100'
  8 WHEN 'B' THEN 'The mark is 80-90'
  9 WHEN 'C' THEN 'The mark is 70-80'
  10 WHEN 'D' THEN 'The mark is 60-70'
  11 WHEN 'E' THEN 'The mark is 0-60'
  12 END;
  13 dbms_output.put_line(res);
  14* end;
  SQL> /

  PL/SQL procedure successfully completed.

  SQL> declare
  2 mygrade char(1):='F';
  3 res varchar2(20);
  4 begin
  5 res :=
  6 CASE mygrade
  7 WHEN 'A' THEN 'The mark is 90-100'
  8 WHEN 'B' THEN 'The mark is 80-90'
  9 WHEN 'C' THEN 'The mark is 70-80'
  10 WHEN 'D' THEN 'The mark is 60-70'
  11 WHEN 'E' THEN 'The mark is 0-60'
  12 ELSE 'The mark is null'
  13 END;
  14 dbms_output.put_line(res);
  15 end;
  16 /
  The mark is null

  PL/SQL procedure successfully completed.

  
  

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