Mysql必读MySQL的CASE WHEN语句的几个使用实例

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本文介绍了MysqL必读MysqL的CASE WHEN语句的几个使用实例，希望对您有用。如果有疑问，可以联系我们。

MysqL数据库使用CASE WHEN进行字符串替换处置

代码以下:MysqL> select * from sales;

MysqL数据库9 rows in set (0.01 sec)

MysqL数据库SELECT name AS name,
    CASE category
    WHEN "HolIDay" THEN "Seasonal"
    WHEN "Profession" THEN "Bi_annual"
    WHEN "literary" THEN "Random" END AS "Pattern"
FROM sales;                   

MysqL数据库9 rows in set (0.00 sec)

MysqL数据库CREATE table sales(
    num MEDIUMINT NOT NulL auto_INCREMENT,name CHAR(20),winter INT,spring INT,
    su妹妹er INT,fall INT,category CHAR(13),primary key(num)
) ENGINE=MyISAM;

MysqL数据库insert into sales value(1,'Java',1067,200,150,267,'HolIDay');
insert into sales value(2,'C',970,770,531,486,'Profession');
insert into sales value(3,'JavaScript',53,13,21,856,'literary');
insert into sales value(4,'sql',782,357,168,250,'Profession');
insert into sales value(5,'Oracle',589,795,367,284,'HolIDay');
insert into sales value(6,'MysqL',953,582,336,489,'literary');
insert into sales value(7,'Cplus',752,657,259,478,'literary');
insert into sales value(8,'Python',67,23,83,543,'HolIDay');
insert into sales value(9,'PHP',673,48,625,52,'Profession');

简单语句
代码以下:
SELECT CASE WHEN 10*2=30 THEN '30 correct'
   WHEN 10*2=40 THEN '40 correct'
   ELSE 'Should be 10*2=20'
END AS `result`;
多重表达式
代码以下:SELECT CASE 10*2
   WHEN 20 THEN '20 correct'
   WHEN 30 THEN '30 correct'
   WHEN 40 THEN '40 correct'
   ELSE 'No results'
END AS `result`;
在SELECT查询中使用CASE WHEN
代码以下:CREATE table DVDs (
   ID SMALliNT NOT NulL auto_INCREMENT PRIMARY KEY,
   name VARCHAR(60) NOT NulL,
   Numdisks tinyint NOT NulL DEFAulT 1,
   ratingID VARCHAR(4) NOT NulL,
   StatID CHAR(3) NOT NulL
) ENGINE=INNODB;
INSERT INTO DVDs (name,Numdisks,ratingID,StatID)
VALUES ('Christmas',1,'NR','s1'),('Doc','G',  's2'),('Africa','PG',('Falcon','s2'),
       ('Amadeus',('Show',2,('VIEw',('Mash','R',  's2');
SELECT name,ratingID AS rating,
   CASE ratingID
      WHEN 'R' THEN 'Under 17 requires an adult.'
      WHEN 'X' THEN 'No one 17 and under.'
      WHEN 'NR' THEN 'Use discretion when renting.'
      ELSE 'OK to rent to minors.'
   END AS Policy
FROM DVDs
ORDER BY name;

MysqL数据库8 rows in set (0.01 sec)

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