MySQL - 5.1 Reference Manual参考手册 - 12.8.6.2. CASE Statement - CASE语句

MySQL - 5.1 Reference Manual参考手册 - 12.8.6.2. CASE Statement - CASE语句

CASE [code]case_value

WHEN

when_value

THEN

statement_list

[WHEN

when_value

THEN

statement_list

] ...
[ELSE

statement_list

]
END CASE
[/code]

Or:

CASE
    WHEN [code]search_condition

THEN

statement_list

[WHEN

search_condition

THEN

statement_list

] ...
[ELSE

statement_list

]
END CASE
[/code]

The

CASE

statement for stored programs implements a complex conditional
construct. If a

search_condition

evaluates to true, the corresponding SQL statement list is
executed. If no search condition matches, the statement list in
the

ELSE

clause is executed. Each

statement_list

consists of one or
more statements.

If no

when_value

or

search_condition

matches the value
tested and the

CASE

statement contains no

ELSE

clause, a
Case not found for CASE statement error
results.

Each

statement_list

consists of one
or more statements; an empty

statement_list

is not allowed. To
handle situations where no value is matched by any

WHEN

clause, use an

ELSE

containing an empty

BEGIN ... END

block, as
shown in this example:

DELIMITER |

CREATE PROCEDURE p()
  BEGIN
    DECLARE v INT DEFAULT 1;
    
    CASE v
      WHEN 2 THEN SELECT v;
      WHEN 3 THEN SELECT 0;
      ELSE
        BEGIN
        END;
    END CASE;
  END;
  |

(The indentation used here in the

ELSE

clause
is for purposes of clarity only, and is not otherwise
significant.)

Note

The syntax of the

CASE

statement used inside stored programs
differs slightly from that of the SQL

CASE

expression described in
Section 11.3, “Control Flow Functions”. The

CASE

statement cannot have an

ELSE NULL

clause,
and it is terminated with

END CASE

instead
of

END

.

[MySQL - 5.1 Reference Manual 参考手册 - 12 SQL Statement Syntax
- SQL语句语法 - 12.8 MySQL Compound-Statement Syntax - MySQL复合语句语法 - 12.8.6
Flow Control Constructs流程控制结构 - 12.8.6.2. CASE Statement - CASE语句 - 文档]

http://dev.mysql.com/doc/refman/5.1/en/case-statement.html

[MySQL - 5.1 Reference Manual参考手册]

MySQL
- 5. 数据库管理 - 5.3. mysqld：MySQL服务器 - 5.3.3. 服务器系统变量 -
max_allowed_packet, http://dev.mysql.com/doc/refman/5.1/zh/database-administration.html#server-system-variables

9.
语言结构 - 9.2. 数据库、表、索引、列和别名 - 9.2.2. 识别符大小写敏感性, http://dev.mysql.com/doc/refman/5.1/zh/language-structure.html#name-case-sensitivity
13. SQL语句语法 - 13.1. 数据定义语句 - 13.1.5. CREATE TABLE语法, http://dev.mysql.com/doc/refman/5.1/zh/sql-syntax.html#create-table 12
SQL Statement Syntax - SQL语句语法 - 12.8 MySQL Compound-Statement Syntax -
MySQL复合语句语法 - 12.8.6 Flow Control Constructs流程控制结构 - 12.8.6.2. CASE
Statement - CASE语句, http://dev.mysql.com/doc/refman/5.1/en/case-statement.html