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为简单起见,假设所有相关字段都是NOT NULL。 你可以做: SELECT table1.this, table2.that, table2.somethingelseFROM table1, table2WHERE table1.foreignkey = table2.primarykey AND (some other conditions) 要不然: SELECT table1.this, table2.that, table2.somethingelseFROM table1 INNER JOIN table2 ON...
我被要求使用下面的SQL语句中使用的低级操作符(join/project/select)来描述命令的顺序;FROM DOG d, KENNEL kAND d.kennel_name = k.name;PROJECT d.name, k.city 但是,除此之外,我不确定您将如何使用联接和
> SQLs have different function. LEFT JOIN should > used for scenario if not all record of > Table1.columnA exist in Table2.columnB. But > assuming it does, which query would be faster? It depends on if there are indexes on columnA or columnB and which index is better etc. In gene...
内连接(INNER JOIN):返回两个表中满足连接条件的行。 自连接(SELF JOIN):将表视为两个独立的实体,通过指定连接条件来连接同一表的两个实例。 外连接(OUTER JOIN):包括左外连接(LEFT JOIN)和右外连接(RIGHT JOIN),返回满足连接条件的行以及未匹配的行。
1、select * form tab1 left join tab2 on (tab1.size = tab2.size) where tab2.name=’AAA’ 2、select * form tab1 left join tab2 on (tab1.size = tab2.size and tab2.name=’AAA’) 第一条SQL的过程: 1、中间表 on条件:
在inner join中是没有区别的,但是在左连接和右连接中,区别就体现出来了,下面以左连接为例: 1、用on的时候,只对右表做筛选条件,而左表不受控制 2、用where的时候,对临时表的组合后的结果进行筛选,所以对左右表... 101欢欢鱼 0 1380 关于SQL中的 where 1 = 1 的用法 ...
where C.status>1 and D.status=1; 1. 2. 3. 4. 5. VS select * from A inner join B on B.name = A.name left join C on C.name = B.name and C.status>1 left join D on D.id = C.id and D.status=1 1. 2. 3.
2019-12-25 19:37 −sql中的连接查询有inner join(内连接)、left join(左连接)、right join(右连接)、full join(全连接)四种方式,它们之间其实并没有太大区别,仅仅是查询出来的结果有所不同。例如我们有两张表: Orders表通过外键Id_P和Persons表进行关联。 1.in... ...
and SELECT * FROM Table1 LEFT JOIN Table2 ON Table1.columnA = Table2.columnB; Which would be executed faster? I understand the 2 SQLs have different function. LEFT JOIN should used for scenario if not all record of Table1.columnA exist in Table2.columnB. But assuming it does, which...