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Mysql必讀MySQL的CASE WHEN語(yǔ)句的幾個(gè)使用實(shí)例

作者：VEPHP   時(shí)間 2017-10-18

《Mysql必讀MySQL的CASE WHEN語(yǔ)句的幾個(gè)使用實(shí)例》要點(diǎn)：
本文介紹了Mysql必讀MySQL的CASE WHEN語(yǔ)句的幾個(gè)使用實(shí)例，希望對(duì)您有用。如果有疑問(wèn)，可以聯(lián)系我們。

MYSQL數(shù)據(jù)庫(kù)使用CASE WHEN進(jìn)行字符串替換處置

代碼以下:
mysql> select * from sales;

MYSQL數(shù)據(jù)庫(kù)9 rows in set (0.01 sec)

MYSQL數(shù)據(jù)庫(kù)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數(shù)據(jù)庫(kù)9 rows in set (0.00 sec)

MYSQL數(shù)據(jù)庫(kù)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數(shù)據(jù)庫(kù)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');


簡(jiǎn)單語(yǔ)句
代碼以下:

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`;

多重表達(dá)式
代碼以下:
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查詢(xún)中使用CASE WHEN
代碼以下:
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', 1, 'G',? 's2'), ('Africa', 1, 'PG', 's1'), ('Falcon', 1, 'NR', 's2'),
?????? ('Amadeus', 1, 'PG', 's2'), ('Show', 2, 'NR', 's2'), ('View', 1, 'NR', 's1'), ('Mash', 2, '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數(shù)據(jù)庫(kù)8 rows in set (0.01 sec)

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