SQL-方法论

写SQL时可以考虑的手段：

1. 行转列
   1. 先分为多个临时表，然后JOIN到一起

   2. select uid,       t1.name YuWen,       t2.name ShuXuefrom (select uid,             name      from tableA      where naem = '语文') t1         join (select uid,                      name               from tableA               where naem = '数学') t2              on t1.uid = t2.uid;

   3. 用sum(if())

   4. select uid,       sum(if(name = '语文')) YuWen,       sum(if(name = '数学')) ShuXuefrom tableAgroup by uid;

2. 列转行
   1. 先分为多个临时表，然后UNION到一起

   2. select uid,       YuWenfrom tableAunion allselect uid,       ShuXuefrom tableA;

来源地址：https://blog.csdn.net/qq_40382400/article/details/132062061