the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
theMySQLoptimizerconsidersmanytechniquestoefficientlyperformthelookupsinvolvedinanSQLquery.Aqueryonahugetablecanbeperformedwithoutreadingalltherows;ajoininvolvingseveraltablescanbeperformedwithoutcomparingeverycombinationofrows.Thesetofoperationsthattheoptimizerchoosestoperformthemostefficientqueryiscalledthe“queryexecution...
. .</sql> <params /> <dsql_operations> <dsql_operation> . . . </dsql_operation> [ . . . n ] <dsql_operations> </dsql_query> XML 标记包含此信息:展开表 XML 标记摘要、属性和内容 <dsql_query> 顶级/文档元素。 <sql> 回显SQL_statement。 <params> 这次不使用此标记。 <...
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
SET odps.sql.allow.fullscan=true; create table shop as select shop_name, customer_id, total_price from sale_detail; Examples Execute the following statements based on the sample data: -- Execute the query statement. select a.customer_id as ashop, sum(a.total_price) as ap,count(b.tot...
If you want to query execution plans with higher readability, we recommend that you upgrade your Hologres instance to V1.3.4x or later. EXPLAIN Syntax You can execute the following EXPLAIN statement to query the execution plan that is estimated by the QO: EXPLAIN <sql>; Example In this ...
The execution plan for a specific Amazon Redshift query statement breaks down execution and calculation of a query into a discrete sequence of steps and table operations that eventually produce a final result set for the query. For information about query planning, seeQuery processing. ...
probe: The total time consumed by the main IndexJoin thread to perform join operations with the hash table of the outer table rows and the inner table rows. IndexHashJoin The execution process of the IndexHashJoin operator is similar to that of the IndexJoin operator. I...
(AWR) SQL Tuning Set (STS) SQL Plan Baseline (SPM) Using the EXPLAIN PLAN Command and the DBMS_XPLAN.DISPLAY Function The following examples illustrate how to generate and display an execution plan for our original SQL statement using the different functions provided in the DBMS_...
3 rows in set (0.00 sec) Output is longer, we can see that three tables are involved in the query. As you can see, EXPLAIN refers to them using aliases defined in a query. By looking at the output we can see that the optimizer decided to start with the ‘actor’ table, using ‘...