可能工作中实际使用的不多,但是不论的自己学习还是面试,都需要掌握的。Explain可以使用在SELECT, DELETE, INSERT, REPLACE, andUPDATE语句中,执行的结果会在每一行显示用到的每一个表的详细信息。简单语句可能结果 子查询 字段 MySQL 转载 dmzhaoq1 2024-03-29 17:11:36...
Query OK,1row affected# 下面possible_keys可能会用到的索引有主键和我建的索引,但是key实际用到的是主键,主键长度是4,ref用的列的名字(或单词“const”,此处用的是常量const,速度快,rows扫描的只有1行mysql> explain select cusno from testa where id=2andname='aaa'; +---+---+---+---+---+--...
{"noCommunity":"Cannot find community","noUser":"Cannot find current user","noNode":"Cannot find node with id {nodeId}","noMessage":"Cannot find message with id {messageId}"},"localOverride":false},"CachedAsset:text:en_US-shared/client/components/common/Loading/LoadingDot-0"...
* may have seen a different subset of batches and we want to find the * highest memory usage for any one batch across all batches. */ if (hashstate->shared_info) { SharedHashInfo *shared_info = hashstate->shared_info; int i; for (i = 0; i < shared_info->num_workers; ++i) ...
Thepossible_keys column indicates which indexes MySQL can choose from use to findthe rows in this table. Note that this column is totally independent of theorder of the tables as displayed in the output from EXPLAIN. That means thatsome of the keys in possible_keys might not be usable in ...
MySQL must do an extra pass to find out how to retrieve the rows in sorted order. The sort is done by going through all rows according to the join type and storing the sort key and pointer to the row for all rows that match the WHERE clause. The keys then are sorted and the rows...
db.collection.findOneAndDelete db.collection.findOneAndReplace() db.collection.findOneAndUpdate() db.collection.getIndexes db.collection.getShardDistribution db.collection.getShardVersion db.collection.hideIndex db.collection.insert db.collection.insertMany db.collection.insertOne db.collection.isCapped db....
The EXPLAIN command provides information about how MySQL executes queries. EXPLAIN can work with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. We'll first analyze the original query, then attempt to optimize the query and look into the optimized query's execution plan to see what chang...
plan_hash_valuefromdba_hist_sqlstat a, dba_hist_snapshot bwherea.snap_id=b.snap_idandsql_id='089dbukv1aanh'orderby2,1 Step3. 如果最近发生解析计划变更,并导致效率变慢,通过SPM绑定之前的解析计划 (脚本coe_xfr_sql_baseline.sql) SQL>@D:\Gavin\coe_xfr_sql_baseline.sql ...
TheSHOW CREATE TABLE,SHOW TABLE STATUS, andSHOW INDEXstatements also provide information about tables. SeeSection 13.7.5, “SHOW Statements”. EXPLAINworks withSELECT,DELETE,INSERT,REPLACE, andUPDATEstatements. WhenEXPLAINis used with an explainable statement, MySQL displays information from the optimizer...