数据表结构：
数据表结构
数据表数据：
数据表数据
查询效果：
查询效果
SQL语句：
SELECT
update_type,
( CASE update_type WHEN 1 THEN "名称" WHEN 2 THEN "编码" WHEN 3 THEN "所属地" END ) AS update_typename,
( CASE update_type WHEN 1 THEN before_name WHEN 2 THEN before_code WHEN 3 THEN before_belong END ) AS before_update,
( CASE update_type WHEN 1 THEN after_name WHEN 2 THEN after_code WHEN 3 THEN after_belong END ) AS after_update
FROM
pch_case
//case···when···语法
CASE case_value
WHEN when_value THEN
statement_list
ELSE
statement_list
END CASE;
