spark-instrumented-optimizer/docs/sql-ref-syntax-qry-select-case.md

---
layout: global
title: CASE Clause
displayTitle: CASE Clause
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  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
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---

### Description

`CASE` clause uses a rule to return a specific result based on the specified condition, similar to if/else statements in other programming languages.

### Syntax

```sql
CASE [ expression ] { WHEN boolean_expression THEN then_expression } [ ... ]
    [ ELSE else_expression ]
END
```

### Parameters
    
* **boolean_expression**

    Specifies any expression that evaluates to a result type `boolean`. Two or
    more expressions may be combined together using the logical
    operators ( `AND`, `OR` ).

* **then_expression**

    Specifies the then expression based on the `boolean_expression` condition; `then_expression` and `else_expression` should all be same type or coercible to a common type.
    
* **else_expression**

    Specifies the default expression; `then_expression` and `else_expression` should all be same type or coercible to a common type.
    
### Examples

```sql
CREATE TABLE person (id INT, name STRING, age INT);
INSERT INTO person VALUES
    (100, 'John', 30),
    (200, 'Mary', NULL),
    (300, 'Mike', 80),
    (400, 'Dan', 50);

SELECT id, CASE WHEN id > 200 THEN 'bigger' ELSE 'small' END FROM person;
+------+--------------------------------------------------+
|  id  | CASE WHEN (id > 200) THEN bigger ELSE small END  |
+------+--------------------------------------------------+
| 100  | small                                            |
| 200  | small                                            |
| 300  | bigger                                           |
| 400  | bigger                                           |
+------+--------------------------------------------------+

SELECT id, CASE id WHEN 100 then 'bigger' WHEN  id > 300 THEN '300' ELSE 'small' END FROM person;
+------+-----------------------------------------------------------------------------------------------+
|  id  | CASE WHEN (id = 100) THEN bigger WHEN (id = CAST((id > 300) AS INT)) THEN 300 ELSE small END  |
+------+-----------------------------------------------------------------------------------------------+
| 100  | bigger                                                                                        |
| 200  | small                                                                                         |
| 300  | small                                                                                         |
| 400  | small                                                                                         |
+------+-----------------------------------------------------------------------------------------------+

SELECT * FROM person
    WHERE 
        CASE 1 = 1 
            WHEN 100 THEN 'big' 
            WHEN 200 THEN 'bigger'
            WHEN 300 THEN 'biggest' 
            ELSE 'small'
        END = 'small';
+------+-------+-------+
|  id  | name  |  age  |
+------+-------+-------+
| 100  | John  | 30    |
| 200  | Mary  | NULL  |
| 300  | Mike  | 80    |
| 400  | Dan   | 50    |
+------+-------+-------+
```

### Related Statements

* [SELECT Main](sql-ref-syntax-qry-select.html)
* [WHERE Clause](sql-ref-syntax-qry-select-where.html)
* [GROUP BY Clause](sql-ref-syntax-qry-select-groupby.html)
* [HAVING Clause](sql-ref-syntax-qry-select-having.html)
* [ORDER BY Clause](sql-ref-syntax-qry-select-orderby.html)
* [SORT BY Clause](sql-ref-syntax-qry-select-sortby.html)
* [DISTRIBUTE BY Clause](sql-ref-syntax-qry-select-distribute-by.html)
* [LIMIT Clause](sql-ref-syntax-qry-select-limit.html)
* [PIVOT Clause](sql-ref-syntax-qry-select-pivot.html)
* [LATERAL VIEW Clause](sql-ref-syntax-qry-select-lateral-view.html)