参考文章 EXPLAIN table_name或:EXPLAIN [EXTENDED] SELECT select_options 前者可以得出一个表的字段结构等等,后者主要是给出相关的一些索引信息。 id id 相同执行顺序由上到下 如果是子查询,id序号会自增,id值越大优先级就越高,越先被执行。 select_type (二)select_type列:数据读取操作的操作类
mysql性能优化---explain详解 1.explain作用 explain语句提供了MySQL如何执行语句的信息。解释选择、删除、插入、替换和更新语句如何工作。 2.如何使用 explain your command; select_type...【MySQL】explain命令详解(三) explain命令的表头 7、ken_len 索引中使用的字节数,可通过该列计算使用索引的长度。该列显示...
With the output appearing in the explain tab SSDT, on the TOOLS menu, select Options. Expand the Text Editor section, expand XML, and then select General. In the Display area, check Line numbers. Select OK.Example EXPLAIN outputThe XML result of the EXPLAIN command with row numbers turned ...
ExplainPropertyText("Command", setopcmd, es); } break; default: break; } if (es->costs) { if (es->format == EXPLAIN_FORMAT_TEXT) { appendStringInfo(es->str, " (cost=%.2f..%.2f rows=%.0f width=%d)", plan->startup_cost, plan->total_cost, plan->plan_rows, plan->plan_...
In the syntax above, sql_statement represents the SQL query you want to analyze, while the option parameter allows you to specify various options for the output of the explain plan command. Some common options include: ANALYZE: Provides more detailed query plan information, including the execution...
explain().find() 该方法与db.collection.find().explain()类似,但是存在以下关键差异 The db.collection.explain() method wraps the explain command and is the preferred way to run explain. db.collection.explain().find() is similar to db.collection.find().explain() with the following key ...
Grad-CAM computes the gradient of a differentiable output, for example class score, with respect to the convolutional features in the chosen layer. The gradients are pooled over space and time dimensions to find the neuron importance weights. These weights are then used to linearly combine the ...
The PostgreSQLexplaincommand has many options of whichanalyze,buffersandsettingsare the most helpful ones. Enabling theanalyzeoption means that the execution plan is not only created, but also executed. That implies that the side effects of running the statement being explained will take place. Such...
If you need (or want) to create a histogram manually you can use the following command. SQL> exec DBMS_STATS.GATHER_TABLE_STATS('HR', 'EMPLOYEES', method_opt=>'FOR COLUMNS SIZE 254 JOB_ID'); With a histogram on JOB_ID in place the optimizer estimates the correct number of rows ...
You can find details in TiDB Query Execution Plan Overview. Currently, EXPLAIN in TiDB outputs 5 columns: id, estRows, task, access object, operator info. Each operator in the execution plan is described by these attributes, with each row in the EXPLAIN output describing an operator. The ...