三、 多行多列子查询 名字叫Multiple Row and Column Subqueries,使用这种语法,in中值的上限可以到10万而不是1000,足够满足绝大多数业务场景。当然,如果真的in 10万个值,性能绝对够呛,慎用… select column_X, ... from my_table where ('magic', column_X ) in ( ('magic', 1), ('magic', 2), (...
4. 使用多行多列子查询(Multiple Row and Column Subqueries) Oracle允许使用一种特殊的语法来处理超过1000个值的IN子句,这种方法通过构造一个包含多行多列的子查询来实现。但是,请注意,这种方法在性能上可能并不优于其他方法,并且当值列表非常大时,可能会导致性能问题。例如: sql SELECT column_X, ... FROM ...
1、单行子查询(=) single-row subqueries 解释:单行子查询是指返回一行数据的子查询语句 2、多行子查询(in) multiple-row subqueries 解释:多行子查询是指返回多行数据的子查询 3、多行子查询使用all操作符 Select ename,sal,deptno from emp where sal>all(select sal from emp where deptno =30); ...
概述 数据库中一些数据文件的绝对文件编号和相对文件编号具有相同的值,但某些数据文件不会。本文档介绍数据库如何分配数据文件的绝对和相对文件编号。 绝对文件编号 绝对文件号在整个数据库中唯一,可以通过V$DATAFILE的FILE#查看,或者DBA_DATA_FILES视图的FILE_ID查看。
the subquery produces asingle XML string column. The XML string for each row holds aggregated datacorresponding to the implicit GROUP BY value of that row. TheXML string for each output row includes all pivot values found by the subquery,even if there are no corresponding rows in the input ...
the ANY keyword produces a single XMLstring column. The XML string for each row holds aggregated data correspondingto the implicit GROUP BY value of that row. However, in contrastto the behavior when you specify subquery, the ANY wildcardproduces an XML string for each output row that includes...
“Foreign Key” indexes and primary key indexes during referential integrity Single table, single column index, multiple statements Unique index (equality and range predicates) non-unique index covering unique constraint non-unique index generally Inlist iterator and union all. Nested loop joins Single...
“Foreign Key” indexes and primary key indexes during referential integrity Single table, single column index, multiple statements Unique index (equality and range predicates) non-unique index covering unique constraint non-unique index generally Inlist iterator and union all. Nested loop joins Single...
You cannot mix and match -- for instance, with PATH of /A, and a column of B/C.TXT it will NOT find /A/B/C.TXT. On some platforms, PATH can specify multiple directories. If you do this, make sure that your documents have unique names -- if a document C.TXT is in ...
A primary key in SQL is a one-column or combination of the column with a unique value for each row or tuple. The value of the primary key must be unique within the table. The purpose is to bind data together, across tables, without repeating all of the data in every table. It enfo...