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How does MySQL CASE work?
The MySQL CASE works like a switch statement. The syntax of CASE is as follows −
Case 1 − Compare Statement
Case when anyCompareStatement then value1 when anyCompareStatement then value2 . . N else anyValue end as anyVariableName;
Case 2 − Conditions
The second syntax can be used when you are selecting only one column. The syntax is as follows −
case yourColumnName when condition1 then result1 when condition1 then result2 . . N else anyValue end;
To understand the above concept, let us use select statement.
Case 1
The query is as follows −
mysql> select -> case when 45 < 55 then '55 is greater than 45' -> when 10!=11 then '10 is not equal to 11' -> else 'Default case' -> end as Result;
Output
+-----------------------+ | Result | +-----------------------+ | 55 is greater than 45 | +-----------------------+ 1 row in set (0.00 sec)
Case 2
Let us create a table to understand the second syntax.
The query to create a table is as follows −
mysql> create table CaseDemo -> ( -> Id int, -> Name varchar(100) -> ); Query OK, 0 rows affected (0.93 sec)
Insert some records in the table using insert command. The query is as follows −
mysql> insert into CaseDemo values(1,'John'); Query OK, 1 row affected (0.43 sec) mysql> insert into CaseDemo values(2,'Sam'); Query OK, 1 row affected (0.16 sec)
Display all records from the table using a select statement. The query is as follows −
mysql> select *from CaseDemo;
Output
+------+------+ | Id | Name | +------+------+ | 1 | John | | 2 | Sam | +------+------+ 2 rows in set (0.00 sec)
Here is the second query of CASE that can be used to work with only one value. The query is as follows −
mysql> select case name -> when 'John' then 'His name is John' -> when 'Sam' then 'His name is Sam' -> else -1 -> end as Result -> from CaseDemo;
Output
+------------------+ | Result | +------------------+ | His name is John | | His name is Sam | +------------------+ 2 rows in set (0.00 sec)
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