Mysql when case condition judgment language name usage

The default Return Value Type of a CASE expression is the compatible set type of any return value, but the specific situation depends on the context. If it is used in a string context, a result flavor string is returned. If it is used in the numeric context, the returned result is a decimal value, real value, or integer value.

Syntax

The Code is as follows:	Copy code
CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result...] [ELSE result] end case when [condition] THEN result [WHEN [condition] THEN result...] [ELSE result] END

Instance

The Code is as follows:	Copy code
Select case when 10*2 = 30 THEN '30 correct' WHEN 10*2 = 40 THEN '40 correct' ELSE 'should be 10*2 = 20' END;

Complexity

 

The Code is as follows:	Copy code
Select case 10*2 WHEN 20 THEN '20 correct' WHEN 30 THEN '30 correct' WHEN 40 THEN '40 correct' END;

Instance

 

The Code is as follows:

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/* Mysql> SELECT Name, RatingID AS Rating, -> CASE RatingID -> WHEN 'r'then' Under 17 requires an adult .' -> WHEN 'X' No one 17 and under .' -> WHEN 'nr 'then' Use discretion when refreshing .' -> 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 refreshing. | | Doc | G | OK to rent to minors. | | Falcon | NR | Use discretion when authentication ing. | | Mash | R | Under 17 requires an adult. | | Show | NR | Use discretion when refreshing. | | View | NR | Use discretion when refreshing. | + ----------- + -------- + ------------------------------ + 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 ('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' No one 17 and under .' WHEN 'nr 'then' Use discretion when processing ing .' ELSE 'OK to rent to minors .' End as Policy FROM DVDs Order by Name;