Current query optimizers are often ill-prepared for the new types of queries as they do not deal well with procedural 'insertions'. In this paper, we discuss the inefficiencies of CASE expressions and present several new optimization techniques to address them. We also describe experimental ...
with_query_name [ ( column_name [, ...] ) ] AS ( {select|values| insert | update |delet...
[WITH with_query [,...]] SELECT expr FROM TABLE WHERE bool_expr GROUP BY columns HAVING Condition ORDER BY expr LIMIT count 在执行顺序上,首先从表中select出需要的列;然后执行WHERE语句;过滤完后,执行GROUP BY聚合计算;聚合后的结果执行HAVING执行二次过滤;然后执行ORDER BY排序结果;最后根据LIMIT限定输...
Full Text Search - WITH QUERY EXPANSION 我们虽然只指定了'SQL'作为关键词,但最终结果也显示了包含'MySQL'的结果(查询扩展下认为它们是有强关联关系的)。 1.3 数值处理函数 Numeric Functions 1.4 日期和时间处理函数 Date and Time Functions 2. 子查询 2.1 什么是子查询 子查询(Subquery)是指嵌套在其它查询中...
WITH表达式的语法如下: [WITH [RECURSIVE] with_query [,…] ] SELECT … 其中,with_query的语法为: with_query_name [ ( column_name [, ...] ) ] AS ( {select | values | insert | update | delete} ) 关键要点如下: 每个CTE的AS语句指定的SQL语句,必须是可以返回查询结果的语句,可以是普通的SE...
[WITH [RECURSIVE] with_query [,…] ] SELECT… 其中,with_query的语法为: with_query_name [ ( column_name [, ...] ) ] AS ( {select | values | insert | update | delete} ) 关键要点如下: 每个CTE的AS语句指定的SQL语句,必须是可以返回查询结果的语句,可以是普通的SELECT语句,也可以是INSERT...
这张图描述了left join(左连接)、right join(右连接) 、inner join(内连接)、outer join(外连接)相关的7种用法。 我改了一版: 感觉更方便理解了 可以关注我公众号,回复“mysql”,可以拿到高清大图 二、四种JOIN的区别 1、INNER JOIN:如果表中有至少一个匹配,则返回行; ...
use of any comparison operator and checking multiple conditions, all in a SQL query itself. Moreover, using the CASE function, multiple conditions provided in separate SQL queries can be combined into one, thus avoiding multiple statements on the same table (example given below). The function is...
case when exists(select 1 from dat_acct_item_21_201607 t7 where t1.prd_inst_id=t7.prd_inst_id and t7.fee_type=1 and exists(select 1 from PAR_ACCT_OFR_RANGE t8 where t7.ofr_id=t8.ofr_id) and exists(select 1 from PAR_ACCT_ACCT_REPLACE t9 ...
查询执行计划可能包含 QueryPlan 元素中的 NonParallelPlanReason 属性,该属性描述未使用并行度的原因。 此属性的值包括:展开表 NonParallelPlanReason 值说明 MaxDOPSetToOne 最大并行度设为 1。 EstimatedDOPIsOne 估计并行度为 1。 NoParallelWithRemoteQuery 远程查询不支持并行度。 NoParallelDynamicCursor 动态游标...