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
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_...
(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_...
摘要: DBA经常会用到的explain来查看SQL语句的执行计划,今天小人斗胆,从MySQL 5.7 Reference Manual中把MySQL EXPLAIN Output Format翻译过来。欢迎拍砖 Explain语句提供了一个select语句执行计划的信息。 Explain为每个用了select语句的表,返回一行信息。它列出了表中的顺序输出,MySQL会读取他们,然后再处理。MySQL解决了所...
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 ...
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: ...
In this stage, the planner: Replaces SQL variable names with column numbers. Infers the type of each expression. Chooses the correct overload for each function. From raw plan to decorrelated plan In this stage, the planner: Replaces subqueries and lateral joins with non-nested operations. ...
Examples 1. Creating a Simple Index CREATE INDEX idx_customer_name ON customers (customer_name); Powered By This example creates an index on the `customer_name` column of the `customers` table, speeding up queries that search by customer names. 2. Using EXPLAIN ANALYZE EXPLAIN ANALYZE SELECT...
TYPESExecute the statement and include the intermediatedata typesCockroachDB chooses to evaluate intermediate SQL expressions. DEBUGExecute the statement and generate a ZIP file containing files with detailed information about the query and the database objects referenced in the query. SeeDEBUGoption. ...