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 ...
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. ...
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. subqueryN: The row refers to the...
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...
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: ...
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 used to create the ...
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...
You can combine the ROLLBACK and EXPLAIN ANALYZE statements to prevent the changes being applied with a query that makes changes to the database, such INSERT, UPDATE, or DELETE. For example: SQL Copy BEGIN; > EXPLAIN ANALYZE INSERT INTO Animal > (ani_id, name, weight_kg, cat_id, enc...
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一.OptimizingQueries with EXPLAIN The EXPLAINstatement can be used either as a way to obtain information about how MySQLexecutes a statement, or as a synonym for DESCRIBE: (1)When youprecede a SELECT statement with the keyword EXPLAIN, MySQL displays informationfrom the optimizer about the query...