第一个sql语句,在on上面写条件,结果是10条数据,数据多了3条,多出来的三条数据,部分列是null。应该是left join的时候,左边有,但是右边没有。所以,在on上写条件,是先出左边的结果,再取右边的。一句话总结就是,on条件在join之前执行ON clause - Before joining. Records (from right table) will be filtered ...
Matters for outer joins a.WHEREclause:Afterjoining. Records will be filtered after join has taken place. b.ONclause -Beforejoining. Records (from right table) will be filtered before joining. This may end up as null in the result (since OUTER join)....
这个貌似和关系型数据库的left join不一样,a表条件加在join之后是没有用的,总会返回a表所有数据,只能加在where条件后面! left semi join/left anti join, 右表只能出现在关联条件(on-clause)里面,件不能出现在where和select子句中。left semi join相当于in的语法。left anti join相当于not in。 selecta.key, ...
The USING clause works for Oracle, PostgreSQL, MySQL, and MariaDB. SQL Server doesn’t support the USING clause, so you need to use the ON clause instead. The USING clause can be used with INNER, LEFT, RIGHT, and FULL JOIN statements. SQL JOIN ON clause with SELECT * Now, if we ch...
Theta join (Non-equi join): In general, this a Theta join used to specify operators or conditions (the ON clause in SQL). In practice, this is a rarely used SQL join types. In most cases, the join will use a non-equality condition e.g. > 1 2 3 4 SELECT p1.FirstName, p2...
JOIN Department WHERE Course.department_id = Department.id;Copy In this example, theJOINstatement performsINNER JOINbetween the two tables. Although both queries return the same result, they serve different purposes. 3.1.ONClause We leverage theONclause in theJOINstatement to specify the conditions ...
ONp.ProductID=sod.ProductID ORDERBYProductNameDESC; GO Note that if you just specify Join by itself, without an Inner keyword in SQL Join clause it will still be an Inner join. You can, of course, put the keyword Inner for clarity sake but if there’s no a left/right tag join it...
Natural Join:creates an implicitjoinclause for you based on the common columns in the two tables being joined. Common columns are columns that have the same name in both tables. ANATURAL JOINcan be an INNERjoin, a LEFT OUTERjoin, or a RIGHT OUTERjoin. The default is INNERjoin. ...
is evaluated before the join occurs. You can think of it as a WHERE clause that only applies to one of the tables. You can tell that this is only happening in one of the tables because the 1000memories permalink is still displayed in the column that pulls from the other table: Filtering...
LEFT OUTER JOIN tab1 t1 ON t1.entity_id = t2.entity_id AND t1.effective_date >= t2.effective_date AND t1.effective_date < ISNULL(t2.ineffective_date, '2900-12-31') WHERE t1.entity_id = 19 Eirikur is correct though, the tab2 effective_date is later than any of the effective ...