sql 中的 case when(mysql 为例)
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; +-----------+--------+------------------------------+ | Name | Rating | Policy | +-----------+--------+------------------------------+ | Africa | PG | OK to rent to minors. | | Amadeus | PG | OK to rent to minors. | | Christmas | NR | Use discretion when renting. | | Doc | G | OK to rent to minors. | | Falcon | NR | Use discretion when renting. | | Mash | R | Under 17 requires an adult. | | Show | NR | Use discretion when renting. | | View | NR | Use discretion when renting. | +-----------+--------+------------------------------+ 8 rows in set (0.01 sec) */ Drop table DVDs; 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 ( 'Ch ristmas ', 1 , 'NR', 's1'), ( 'Do c ', 1 , 'G' , 's2'), ( 'Af rica ', 1 , 'PG', 's1'), ( 'Fa lcon ', 1 , 'NR', 's2'), ( 'Am adeus ', 1 , 'PG', 's2'), ( 'Sh ow ', 2 , 'NR', 's2'), ( 'Vi ew ', 1 , 'NR', 's1'), ( 'Ma sh ', 2 , 'R' , 's2'); SELECT Name, RatingID AS Rating, CASE RatingID WHEN 'R' THEN 'Un der 17 requires an adult. ' WHEN 'X' THEN 'No one 17 and under. ' WHEN 'NR' T HEN 'Us e discretion when renting. ' ELSE 'OK to rent to minors. ' END AS Policy FROM DVDs ORDER BY Name;
发布日期:2021-09-22 22:47:11
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