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...
EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. EXPLAIN与SELECT、DELETE、INSERT、REPLACE和UPDATE语句一起工作。 When EXPLAIN is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan. That is, MySQL explains how it...
{explainable_stmt|FORCONNECTION connection_id} {EXPLAIN|DESCRIBE|DESC} ANALYZE select_statement explain_type: { FORMAT=format_name } format_name: { TRADITIONAL|JSON|TREE } explainable_stmt: {SELECTstatement|TABLEstatement|DELETEstatement|INSERTstatement|REPLACE statement|UPDATEstatement } 示例: EXPLAIN fo...
Using join buffer (Block Nested Loop), Using join buffer (Batched Key Access) 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(…...
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...
However, cross joins consume more memory resources than nested loop joins. The following figure shows the execution plan. The Cross Join operator is displayed. This indicates that the SQL statement uses the cross join. If you want to disable cross joins, execute the following SQL statements ...
缺省falseauto_explain.log_triggers - 包含执行计划中的触发器统计,缺省falseauto_explain.log_format - 日志格式,缺省TEXTauto_explain.log_level - 日志级别,缺省LOGauto_explain.log_nested_statements - 是否记录嵌套语句,缺省falseauto_explain.log_timing - 是否记录时间指标,缺省falseauto_explain.sample_rate ...
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(…) 这些指示索引扫描如何合并为index_merg...
Nested LoopnloopLeast optimal join; mainly used for cross-joins (Cartesian products; without a join condition) and some inequality joins. Hash JoinhjoinAlso used for inner joins and left and right outer joins and typically faster than a nested loop join. Hash Join reads the outer table, hash...
Using join buffer (Block Nested Loop), Using join buffer (Batched Key Access)使用Block Nested Loop或Batched Key Access算法提高join的性能。详见 cnblogs.com/chenpingzha Using MRR使用了Multi-Range Read优化策略。详见 “Multi-Range Read Optimization” Using sort_union(…), Using union(…), Using ...