# `CASE` 表达式

__*CASE 表达式*__

+ 例如:
  + `select case when null='' then true when null<>'' then false else '=)' end;` 
  + `select case null when '' then true when 0 then false else '=)' end;` 
```8
tidb> SELECT 
   -> ~!@case@!~ 
   -> when null='' then true 
   -> when null<>'' then false 
   -> else '=)' end;
+--------------------------------------------------------------------+
| case when null='' then true when null<>'' then false else '=)' end |
+--------------------------------------------------------------------+
| =)                                                                 |
+--------------------------------------------------------------------+
1 row in set (0.00 sec)
tidb> SELECT 
   -> ~!@case null@!~ 
   -> when '' then true 
   -> when 0 then false 
   -> else '=)' end;
+-------------------------------------------------------------+
| case null when '' then true when 0 then false else '=)' end |
+-------------------------------------------------------------+
| =)                                                          |
+-------------------------------------------------------------+
1 row in set (0.00 sec)
```
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[no notes]