Jan 28, 2021 sabriakter This is a better way of reviewing the formula and the Nested If statement:=IF($B$11>DATE(103,1,1), IF($B$11<DATE(103,12,31),MAX(DATE(103,1,1),$B$11),""), IF($B$11<DATE(103,1,1),DATE(103,1,1),""))The first line is checking if cell...
E:using index:查询时不需要回表查询,直接通过索引就可以获取查询的数据。 F:using join buffer(block nested loop),using join buffer(batched key accss):5.6.x之后的版本优化关联查询的BNL,BKA特性。主要是减少内表的循环数量以及比较顺序地扫描查询。 G:using sort_union,using_union,using intersect,using so...
在优化sql语句时,我们经常会用到explain语句,这里对explain语句做一个详细的总结说明。 The EXPLAIN statement provides information about how MySQL executes statements. EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. 通过一个实例来说明explain的用法,其实使用很简单,主要是通过实例来介...
例如,PostgreSQL 有一个prepareThreshold 设置,其默认值为5。该值告诉PostgreSQL 在切换到使用通用计划的服务器端Prepared Statement 之前,它可以在客户端模拟Prepared Statement 多少次。 如果慢速查询使用通用计划,即使运行 EXPLAIN ANALYZE(它会动态生成执行计划),您也可能无法获得相同的计划。 因此,分析慢速查询的一个更...
/* * ExecutorStart hook: start up logging if needed */ static void explain_ExecutorStart(QueryDesc *queryDesc, int eflags) { /* * At the beginning of each top-level statement, decide whether we'll * sample this statement. If nested-statement explaining is enabled,...
Hash Join hjoin Also used for inner joins and left and right outer joins and typically faster than a nested loop join. Hash Join reads the outer table, hashes the joining column, and finds matches in the inner hash table. Step can spill to disk. (Inner input of hjoin is hash step ...
使用Block Nested Loop或Batched Key Access算法提高join的性能。详见https://www.cnblogs.com/chenpingzhao/p/6720531.html Using MRR 使用了Multi-Range Read优化策略。详见“Multi-Range Read Optimization” Using sort_union(…), Using union(…), Using intersect(…) ...
| DELETE statement | INSERT statement | REPLACE statement | UPDATE statement } 示例: EXPLAIN format = TRADITIONAL json SELECT tt.TicketNumber, tt.TimeIn, tt.ProjectReference, tt.EstimatedShipDate, tt.ActualShipDate, tt.ClientID, tt.ServiceCodes, tt.RepetitiveID, ...
When EXPLAIN is used with FOR CONNECTION connection_id rather than an explainable statement, it displays the execution plan for the statement executing in the named connection. See Section 8.8.4, “Obtaining Execution Plan Information for a Named Connection”. 当EXPLAIN与FOR CONNECTION connection_id...
EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first...