交叉连接的:交叉连接会产生笛卡尔积; 自然连接:自然连接可以自动匹配关联字段消除笛卡尔积; ON子句 USING子句 全外连接:如果要实现全外连接只能够依靠SQL:1999语法。LEFT|RIGHT|FULL OUTER JOIN 五、数据的集合运算 数据的集合操作:UNION、UNION ALL、INTERSECT、MINUS 集合操作时,各个查询语句返回的结构要求一致 开发之...
1 2 SQL > select * from a except select * from a; Empty set (0.0015 sec) Ideally, I would like to put parens around the two select statements when using UNION, INTERSECT, and EXCEPT, as seen in the following example, to make the query more explicit. ...
(Of course using UNION ALL is much faster than UNION since we don't need to sort the result. But it violates the requirements) Suppose we are searching population and area, Given that MySQL usually uses one one index per table in a given query, so when it uses the 1st index rather th...
UNION, EXCEPT and INTERSECT can be used within an INSERT statement. The FOR BROWSE clause cannot be used in statements that involve the UNION, EXCEPT and INTERSECT operators. See Also Reference SELECT (Transact-SQL) UNION (Transact-SQL)
可以看到,有一个主键,有一个普通索引,我执行如下 SQL: select * from actor where actor_id<10 and last_name='WAHLBERG' 执行计划如下: 可以看到,用到了索引合并,且是Using intersect。 2.2 Using union(...) 求并集的跟求交集的比较像,就是 AND 变成了 OR。
Duplicate groupings are retained as they would be by using UNION ALL. Note CUBE, ROLLUP and GROUPING SETS do not support the CHECKSUM_AGG function. Composite and Concatenated Elements Multiple columns that are in inner parentheses in theGROUPING SETS list are treated as a single set. For ...
Using temporary表示由于排序没有走索引、使用union、子查询连接查询、使用某些视图等原因。因此创建了一个内部临时表。注意这 里的临时表可能是内存上的临时表,也有可能是硬盘上的临时表,理所当然基于内存的临时表的时间消耗肯定要比基于硬盘的临时表的实
SELECTA, B, 'A1' ...UNION SELECTX, Y, 'B2'... When a row is returned, it includes a value (either A1 or B2) to indicate the table that is the source of the row's values. If the column names in the union are different, SQL uses the set of column names specified in the fir...
UNION是一种在MS SQL Server中使用的操作符,用于合并两个或多个SELECT语句的结果集。它将两个结果集的行组合在一起,并自动去除重复的行。 使用UNION可以将多个查询的结果合并为一个结果集。例如,假设有两个表格,一个存储了学生的英语成绩,另一个存储了学生的数学成绩,可以使用UNION将两个表格的成绩合并为一个...
Return the result set. This is a UNION ALL of T0 to Tn. Example The following example shows the semantics of the recursive CTE structure by returning a hierarchical list of employees, starting with the highest ranking employee, in the Adventure Works Cycles company. A walkthrough of the code...