Mysql将列转换为行（数据透视表）

I have a table like this

我有一张这样的桌子

+---+-----+----+----+----+----+
|id |month|col1|col2|col3|col4|
+---+-----+----+----+----+----+
|101|Jan  |A   |B   |NULL|B   |
+---+-----+----+----+----+----+
|102|feb  |C   |A   |G   |E   |
+---+-----+----+----+----+----+
+---+---