INSERT: 批量插入结果集方式

insert: 批量插入结果集

1. insert into table
   select x,y from a
   union select z,k from b ;
2. insert into table
   select x,y,z from a where 1=1;
   3.批量导入表数据 ，不导入表约束
   select x,y,z into b from a where 1=1;