mysql经典问题,将行转为列。
原表
sum(if(条件,列值,0))语法用例:
select name,sum(if(subject="语文",score,0)) as “语文” from grade GROUP BY name
if中第一个参数为条件,符合条件的内容才会将第二个参数相加,不符合的内容将第三个参数相加。
第二个参数为要相加的参数,可以用常量,也可以用字段值。
第三个参数为条件为假时相加的值,通常设为0.
为了将行转为列(这种操作一般用于统计),可使用如下语句:
select name,sum(if(subject="语文",score,0)) as “语文”,
sum(if(subject="数学",score,0)) as “数学”,sum(if(subject="英语",score,0)) as “英语”
from grade GROUP BY name
结果: