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...
. .</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。 <...
theMySQLoptimizerconsidersmanytechniquestoefficientlyperformthelookupsinvolvedinanSQLquery.Aqueryonahugetablecanbeperformedwithoutreadingalltherows;ajoininvolvingseveraltablescanbeperformedwithoutcomparingeverycombinationofrows.Thesetofoperationsthattheoptimizerchoosestoperformthemostefficientqueryiscalledthe“queryexecution...
In a SQL Server environment, blob storage will typically be used for database backups, using SQL Server’s back up to URL functionality. File Storage - File storage is effectively a file share that can be mounted inside a virtual machine, without the n...
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 ...
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...
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_...
Note:The EXPLAIN command cannot be used for the Database operations and DDL commands other than creating a table, insert, delete, select, select into and update. Examples of Redshift EXPLAIN Given below are the examples to see the implementation of the EXPLAIN command with SQL queries: ...