<dsql_query>最上層/文件元素。 <sql>回應SQL_statement。 <params>目前不使用此標記。 <materialized_view_candidates> (預覽)包含建議具體化檢視的 CREATE 陳述式,可讓 SQL 陳述式有較好的效能。 <dsql_operations>摘要說明和包含查詢步驟,並包含查詢的成本資訊。 也包含所有<dsql_operation>區塊。 此標記包含...
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
With the cost-based optimizer, execution plans can and do change as the underlying costs change.EXPLAINPLANoutput shows how Oracle runs the SQL statement when the statement was explained. This can differ from the plan during actual execution for a SQL statement, because of differences in the exe...
In addition to reclaiming space, it also ensures indexes are effective.When the vacuum process is triggered automatically, the process is known as autovacuum. The frequency with which the process needs to run will depend on the number of update and delete operations. You can...
If you want to query execution plans with higher readability, we recommend that you upgrade your Hologres instance to V1.3.4x or later. EXPLAIN Syntax You can execute the following EXPLAIN statement to query the execution plan that is estimated by the QO: EXPLAIN <sql>; Example In this ...
SET odps.sql.allow.fullscan=true; create table shop as select shop_name, customer_id, total_price from sale_detail; Examples Execute the following statements based on the sample data: -- Execute the query statement. select a.customer_id as ashop, sum(a.total_price) as ap,count(b.tot...
Sorts are expensive operations especially on large tables where the rows do not fit in memory and spill to disk. By default sort blocks are placed into the buffer cache. This may result in aging out of other blocks that may be reread by other processes. To avoid this you can use the pa...
CREATEINDEXidx_value_3ONkvstore(valueASC)INCLUDE(key); If you run the same query, you should see the following output: 1# EXPLAIN (ANALYZE, DIST, COSTS OFF) SELECT * FROM kvstore WHERE value LIKE 'ca%' ORDER BY VALUE;2QUERY PLAN3---4Index Only Scan using idx_value_3 on kvstore (a...
DEGREEINTEGERIf the RETURN operator represents the return fromcolumn-organizeddata processing of the insertion, update, or deletion of rows, the DEGREE argument indicates the number ofcolumn-organizedprocessing subagents that are used to process the insert, update, or delete operations in parallel. ...
(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_...