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...
With the help ofEXPLAIN, you can see where you should add indexes to tables so that thestatement executes faster by using indexes to find rows. You can also useEXPLAIN to check whether the optimizer joins the tables in an optimal order. Togive a hint to the optimizer to use a join orde...
We recommend that you prevent non-equivalent joins in SQL statements. The following code provides an example of a nested loop join. BEGIN; CREATE TABLE public.nestedloop_test_1 ( a integer not null, b integer not null ); CALL set_table_property('public.nestedloop_test_1', 'distribution_...
You cannot usethe EXTENDED and PARTITIONS keywords together in the same EXPLAIN statement. In addition, neither of these keywordscan be used together with the FORMAT option. (FORMAT=JSON causesEXPLAIN to display extended and partition informationautomatically; using FORMAT=TRADITIONAL has no effect on ...
select_type:SIMPLE table:user type:ALL possible_keys:NULL key:NULL key_len:NULL ref:NULL rows:7 Extra:Usingwhere 1rowinset(0.00sec) 一.OptimizingQuerieswithEXPLAINTheEXPLAINstatementcanbeusedeitherasawaytoobtaininformationabouthowMySQLexecutesastatement,orasasynonymforDESCRIBE: ...
select_type: SIMPLE table: user type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 7 Extra: Using where 1 row in set (0.00 sec) 一.OptimizingQueries with EXPLAIN The EXPLAINstatement can be used either as a way to obtain information about how MySQLexecutes a stateme...
(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_...
the default in MySQL 9.3, and is used in the examplesalready shown in this section. Version 2 of the JSON output format is based on access paths, and is intended to provide compatibility with future versions of the MySQLOptimizer. You can switch to the Version 2 format by setting the ...
JOINs Let’s see what the EXPLAIN output of more complex query looks like. We’ll try to find all films released in the year of 2006 where the actor with a last name of ‘MIRINDA’ starred. mysql> EXPLAIN SELECT title, description FROM film AS f JOIN film_actor AS fa ON f.film_id...
In this case, the statement displays information only for the named column. wild, if given, is a pattern string. It can contain the SQL % and _ wildcard characters. In this case, the statement displays output only for the columns with names matching the string. There is no need to ...