刚刚同时跑来问我一个sql语句顿时,一看我有点蒙,由于以前没有用过,因此在这里写下学习笔记加深印象。
语法以下:
sql
CASE value WHEN [compare-value01] THEN result01 [WHEN [compare-value02] THEN result01 ...] [ELSE result] END
此sql语句我认为有点像条件语句。
意思是:
条件一,当字段value的值等于"compare-value"时,赋值为result01;
条件二,当字段value的值等于"compare-value"时,赋值为result02;
...
条件N,,赋值为result02;
结束学习
这么说确定感受很抽象,上实例,一看就明白了。spa
usersa表及数据以下图.net
样例1查询SQLcode
select *, (CASE username WHEN "李四" THEN "四" WHEN "张三" THEN "三" ELSE 'more' END )as "Column" FROM usersa;
查询结果图htm
样例2查询SQL
io
select sex, count(case username when "李四" then "李四" end) as "李四", count(case username when "张三" then "张三" end) as "张三" from usersa group by sex;
查询结果图class
【参考资料】select
http://www.jb51.net/article/28222.htmsql语句