注意观察上面的SQL语句,t1,t2表都被访问了2次,而且t1表2次访问都是同一条SQL语句(子查询),t2表也被访问了2次,但是2次的SQL结构基本一样,所以这里可以用with as优化该SQL WITH b AS (SELECT * FROM t1 WHERE id<100), a as (select * from t2 where id<100) SELECT a.sex, b.* FROM a inner ...
思路 就跟 这个博客一样的http://blog.csdn.net/robinson1988/article/details/10551467我靠 居然还个sb在乱评论 因为in里面有点复杂,不好用hint,我偷懒,难得去搞了,直接 用下面的sql 优化 with x as (SELECT /*+ materialize */ "VOUCHER".FID "ID" FROM T_GL_Voucher "VOUCHER" INNER JOIN T_GL_Vou...
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一、hivesql中(注意:mysql不支持),with as语句的作用是相当于创建了一个中间表,加载到内存中,这样在后续的使用中极大的提高速度(不用建表,insert数据到中间表;加载内存,使用数据速度快)。 二、使用 WITH t1 AS ( SELECT * FROM carinfo ), t2 AS ( SELECT * FROM car_blacklist ) SELECT * FROM t1, ...
WITHsubquery_nameAS(the aggregationSQLstatement)SELECT(query naming subquery_name); With查询语句不是以select开始的,而是以“WITH”关键字开头。 可认为在真正进行查询之前预先构造了一个临时表TT,之后便可多次使用它做进一步的分析和处理 优点 使用SQL with 子句的优点, ...
1 语法：WITHsubquery_nameAS(the aggregation SQL statement)SELECT(query naming subquery_name);2 创建测试表tbl1、tbl2，往tbl1里插入2条数据，往tbl2里插入1000000条数据 3 此时我们单看一下全表扫描tbl2时的情况。通过下图，我们看到单对tbl2全表扫描时的逻辑读为6911 4 下面我们构造一个相关子查询，看看...
The SQL JOIN statement is used to combine rows from two tables based on a common column and selects records that have matching values in these columns. Example -- join the Customers and Orders tables -- based on the common values of their customer_id columns SELECT Customers.customer_id, ...
can you add colour to a fields output in T-SQL? Can you change the value of yes or no instead of true or false use data type (BIT) ? Can you have a TRY CATCH in dynamic SQL? Can you Select From (another query)? Can you use a case statement as part of a left join Can't ...
If it's only about SQL statement text you may use Oracle database tools such as SQL Developer, SQLcl or SQL*Plus. In all these utilities there are history functions available. But if you want to get more information e.g. about execution performance then of course SQL Tuning Sets can be...
Transact-SQL 语法约定 语法 syntaxsql复制 [WITH<common_table_expression>[ ,...n ] ]<common_table_expression>::=expression_name[ (column_name[ ,...n ] ) ]AS(CTE_query_definition) 参数 expression_name 公用表表达式的有效标识符。 expression_name 须不同于在同一WITH <common_table_expression>子...