MySQL的CASE WHEN語句的幾個應用實例。本站提示廣大學習愛好者：（MySQL的CASE WHEN語句的幾個應用實例）文章只能為提供參考，不一定能成為您想要的結果。以下是MySQL的CASE WHEN語句的幾個應用實例正文
應用CASE WHEN停止字符串調換處置
mysql> select * from sales;
9 rows in set (0.01 sec)
SELECT name AS Name,
CASE category
WHEN "Holiday" THEN "Seasonal"
WHEN "Profession" THEN "Bi_annual"
WHEN "Literary" THEN "Random" END AS "Pattern"
FROM sales;
9 rows in set (0.00 sec)
CREATE TABLE sales(
num MEDIUMINT NOT NULL AUTO_INCREMENT, name CHAR(20), winter INT, spring INT,
summer INT, fall INT, category CHAR(13), primary key(num)
) ENGINE=MyISAM;
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');
簡略語句
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`;
多重表達式
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查詢中應用CASE WHEN
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;
8 rows in set (0.01 sec)
