![]() To_char(timestamp ' 17:31:12.66', 'HH12:MI:SS') → 05:31:12Ĭonverts interval to string according to the given format. In this tutorial, you have learned how to use the PostgreSQL EXPLAIN statement to show the query’s plan for a specific SQL statement.To_char ( timestamp with time zone, text ) → textĬonverts time stamp to string according to the given format. To add the actual runtime statistics to the output, you need to execute the statement using the ANALYZE option: EXPLAIN ANALYZE ![]() The following example returns a plan for a statement that joins multiple tables: EXPLAIN The following example displays the plan for a query that uses an aggregate function: EXPLAIN SELECT COUNT(*) FROM film To suppress the cost, you can use the COSTS option: EXPLAIN (COSTS FALSE) SELECTįilm_id = 100 Code language: PHP ( php ) In the output, the planner used an index scan instead of a sequential scan on the film table. EXPLAIN SELECT * FROM film WHERE film_id = 100 īecause the film_id is indexed, the statement returned a different plan. The following example shows the plan for a query that returns a film by a specific film_id. The following statement shows the plan for a simple query on the film table: EXPLAIN SELECT * FROM film ![]() This parameter is set to TEXT by default. Specify the output format of the query plan such as TEXT, XML, JSON, and YAML. Note that when ANALYZE option is used, the summary information is included by default. The SUMMARY parameter adds summary information such as total timing after the query plan. The TIMING defaults to TRUE and it may only be used when ANALYZE is enabled. This parameter includes the actual startup time and time spent in each node in the output. By default, the BUFFERS parameter set to FALSE. BUFFERS only can be used when ANALYZE is enabled. This parameter adds information to the buffer usage. The COSTS option includes the estimated startup and total costs of each plan node, as well as the estimated number of rows and the estimated width of each row in the query plan. The VERBOSE parameter allows you to show additional information regarding the plan. The ANALYZE statement actually executes the SQL statement and discards the output information, therefore, if you want to analyze any statement such as INSERT, UPDATE, or DELETE without affecting the data, you should wrap the EXPLAIN ANALYZE in a transaction, as follows: BEGIN ![]() The ANALYZE option causes the sql_statement to be executed first and then actual run-time statistics in the returned information including total elapsed time expended within each plan node and the number of rows it actually returned. If you omit the boolean, it defaults to ON. You can use TRUE, ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean specifies whether the selected option should be turned on or off. Where option can be one of the following: ANALYZE įORMAT Code language: JavaScript ( javascript ) The following shows the syntax of the EXPLAIN statement: EXPLAIN ) ] sql_statement Code language: CSS ( css ) The most important and useful information that the EXPLAIN statement returns are start-cost before the first row can be returned and the total cost to return the complete result set. The EXPLAIN shows how tables involved in a statement will be scanned by index scan or sequential scan, etc., and if multiple tables are used, what kind of join algorithm will be used. The EXPLAIN statement returns the execution plan which PostgreSQL planner generates for a given statement. Introduction to PostgreSQL EXPLAIN statement Summary: in this tutorial, you have learned how to use the PostgreSQL EXPLAIN statement to display the execution plan of a statement.
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