2.filter --过滤,如not in、min函数等容易产生 Has a number of different meanings, used to indicate partition elimination, may also indicate an actual filter step where one row source is filtering, another, functions such as min may introduce filter steps into query plans. 3.view --视图,大都...
For performance reasons, the query engine can rewrite a join query into a different join type to produce the same results. For example, an inner join query with predicate on one table can be rewritten into a CrossJoin. This pushes the predicate down to the scanning phase of the table so ...
HashAggregateaggrOperator/step for grouped aggregate functions. Can operate from disk by virtue of hash table spilling to disk. GroupAggregateaggrOperator sometimes chosen for grouped aggregate queries if the Amazon Redshift configuration setting for force_hash_grouping setting is off. ...
(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_...
* may have seen a different subset of batches and we want to find the * highest memory usage for any one batch across all batches. */ if (hashstate->shared_info) { SharedHashInfo *shared_info = hashstate->shared_info; int i; for (i = 0; i < shared_info->num_workers; ++i) ...
HashAggregate: Data is hash-calculated, distributed to different shards based on hash values, and then aggregated by using the Gather operator. This type of aggregate is most commonly used. EXPLAIN SELECT l_orderkey,count(l_linenumber) FROM public.holo_lineitem_100g GROUP BY l_orderkey; Mu...
privilege if the specified connection belongs to a different user. The explain_ systemvariable determines the format of the output from EXPLAIN when used to display a query execution plan. Thisvariable can take any of the values used with the FORMAT option, with the addition of DEFAULT as...
EXPLAIN PLAN saves information about an execution plan into the PLAN_TABLE table. Different from the EXPLAIN statement, EXPLAIN PLAN only saves plan information and does not print information on the screen. Precautions EXPLAIN PLAN cannot be executed on a DN. Plan information cannot be collected fo...
PostgreSQL 8.4 syntax is much richer than that of MySQL. The former can use the analytic functions, recursive CTE's and proprietary syntax extensions, all of which can be used for this task. Let's create a sample table: Read the rest of this entry » Share this: Facebook X Written...
Has a number of different meanings, used to indicate partition elimination, may also indicate an actual filter step where one row source is filtering, another, functions such as min may introduce filter steps into query plans. 3.view --视图,大都由内联视图产生(可能深入到视图基表) ...