从笛卡尔积的角度讲就是从笛卡尔积中挑出ON子句条件成立的记录,然后加上左表中剩余的记录,最后加上右表中剩余的记录。另外MySQL不支持OUTER JOIN,但是我们可以对左连接和右连接的结果做UNION操作来实现。连接后的筛选结果依然正常使用group by having等函数 七Case when...
4.4 方法四:left join where ... is not null selectdistinct别名1.相同字段from表格1别名1leftjoin表格2别名2on表格1.相同字段=表格2.相同字段where别名1.相同字段isnotnull; 我们可以这样拆分:1.先左连接把数据全联集起来:select*from表格1别名1leftjoin表格2别名2on表格1.相同字段=表格2.相同字段;2.再加w...
SELECT 'testPA' AS INDIC_KEY, A.CUST_NO AS OBJ_KEY, CASE WHEN B.CUST_NO IS NULL THEN 1 ELSE END AS INDICVAL1,'2222-06-06' AS GRADING_DATE FROM testDB.Table1 A LEFT JOIN ( SELECT DISTINCT T.CUST_NO FROM testDB.TABLE_TRANSACTION T WHERE EXISTS (SELECT 1 FROM testDB.Table1 T...
left join ( select * from producer where merchant_id = 10007 and store_id = 20007 ) store on merchant.barCode = store.barCode ) t where 1 = 1 AND t.itemTitle like concat('%', '士尼-哈哈', '%') AND t.type = 1 limit 0, 10; 2、执行计划 回到顶部 二、优化分析 1、分析 1)改...
内联结-inner join on :查找出同时存在两张表中的数据。先取出符合条件的行,然后交叉联结。 外联结:左联结-left join 和右联结- right join 左联结:以左边的表为主表,先把左表全部取出,再取出右边符合条件的行,最后交叉联结。 右联结:以右边的表为主表,先把右表全部取出,再取出左边符合条件的行,最后交叉联...
左外连接left join:不仅显示两表匹配的数据 还会显示 左表中不匹配的数据 select * from dept d left join emp e on d.deptno = e.deptno; 右外连接right join: 不仅显示两表匹配的数据 还会显示 右表中不匹配的数据 select * from dept d right join emp e on d.deptno = e.deptno; ...
CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ... ELSE result END; 优势 灵活性:可以根据多个条件返回不同的结果。 可读性:代码结构清晰,易于理解和维护。 性能:相对于多个IF语句,CASE WHEN通常具有更好的性能。 类型 简单CASE表达式: ...
*/ SELECT game.mdate, game.team1, SUM(CASE WHEN goal.teamid=game.team1 THEN 1 ELSE 0 END) AS score1, game.team2, SUM(CASE WHEN goal.teamid=game.team2 THEN 1 ELSE 0 END) AS score2 FROM game LEFT JOIN goal ON (goal.matchid = game.id) GROUP BY game.mdate,game.team1,game...
LEFT JOIN forecast2.pricing ON ( CASE pricing.location WHEN '' THEN pricing.location LIKE '%' ELSE pricing.location = mo.location END AND CASE pricing.uniloc WHEN '' THEN pricing.uniloc LIKE '%' ELSE pricing.uniloc = mo.uniloc END AND ...
Date: October 23, 2009 10:29PM Yeah, those CASEs in the JOIN are bad news. Even this would be better, but not much: CASE pricing.type WHEN '' THEN pricing.type LIKE '%' ELSE pricing.type = ma.type END AND --> (pricing.type = '' OR pricing.type = ma.type) AND ...