数据库表横表变纵表

主要用 case...when...then...else...end

创建数据库表

插入数据：

insert into sales(years, month, sales) value('2011', 1, 3);

insert into sales(years, month, sales) value('2011', 2, 2);

insert into sales(years, month, sales) value('2011', 3, 4);

insert into sales(years, month, sales) value('2011', 4, 1);

insert into sales(years, month, sales) value('2012', 1, 1);

insert into sales(years, month, sales) value('2012', 2, 2);

insert into sales(years, month, sales) value('2012', 3, 2);

insert into sales(years, month, sales) value('2012', 4, 3);

变换