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variable is not updated. MySQL 8.4 supports a FOR SCHEMA clause, which causes EXPLAIN to behaveas if the statement to be analyzed had been executed in the named database; FOR DATABASE is supported as a synonym. A simple example of use is shown here: mysql> USE b; Database changed...
This tutorial describes how to use Explain reports to locate and fix problematic (slow) queries. It uses the DBT-3 database and begins with the following simple query example. SELECT * FROM orders WHERE YEAR(o_orderdate) = 1992 AND MONTH(o_orderdate) = 4 AND o_clerk LIKE '%0223';As...
Database Specific Notes DB2:For DB2, the tables used by DB2 for storing the explain plan information should be created before using the explain plan tool. The tables should be created in the schema used to log in to the database. The DB2 installation should come with a script that can be...
DFEPipelineScan – Scans the database for the given pattern argument, with or without a given filter on column(s). DFEProject – Takes multiple input columns and projects only the desired columns. DFEReduce – Performs the specified aggregation function on specified variables. DFERelationalJoin –...
If the FE node version and SE version are inconsistent with the schema version, schema latency may occur. If a large number of DDL statements are executed on the partitioned parent table, the processing speed of SE is slow and the latency is high. As a result, data write and read are ...
EXPLAIN performance is sometimes influenced by the time it takes to create temporary tables. For example, a query that uses the common subexpression optimization requires temporary tables to be created and analyzed in order to return the EXPLAIN output. The query plan depends on the schema and sta...
unionM,N: The row refers to the union of the rows with id values of M and N. derivedN: The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause. ...
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UseEXPLAIN ANALYZEwithout an option, or equivalently with theDISTSQLoption, to execute a query and generate a link to a physical query plan with execution statistics. For example, the followingEXPLAIN ANALYZEstatement executes a simple query against theTPC-H databaseloaded to a 3-node CockroachDB...