1、两个表:table_a和table_b,求两表的交集,关键字:INNER JOIN SELECT a.*,b.* FROM table_a AS a INNER JOIN table_b AS b ON a.id=b.id; 2、两个表:table_a和table_b,table_a为主表,关联查询table_b,table_b有数据就显示,没有数据就显示null,关键字:LEFT JOIN SELECT a.*,b.* FROM table_a AS a LEFT JOIN table_b AS b ON a.id=b.id; 3、两个表:table_a和table_b,table_b为主表,关联查询table_a,table_a有数据就显示,没有数据就显示null,关键字:RIGHT JOIN SELECT a.*,b.* FROM table_a AS a RIGHT JOIN table_b AS b ON a.id=b.id; 4、两个表:table_a和table_b,求table_a表中有且table_b表没有的数据 SELECT a.*,b.* FROM table_a AS a LEFT JOIN table_b AS b ON a.id=b.id WHERE b.id IS NULL; 5、两个表:table_a和table_b,求table_b表中有且table_a表没有的数据 SELECT a.*,b.* FROM table_a AS a RIGHT JOIN table_b AS b ON a.id=b.id WHERE a.id IS NULL; |
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