执行计划生成(Execution Plan Generation):在优化过程中,MySQL会生成一个执行计划,描述了如何执行查询。执行计划通常是一个查询执行树,它包括了表的访问顺序、连接方法、过滤条件等信息。 执行(Execution):一旦生成了执行计划,MySQL就会按照执行计划的步骤开始执行查询。这包括打开表、读取数据、应用过滤条件、进行连接等操...
SELECT STATEMENT [CHOOSE] Cost=1 INDEX UNIQUE SCAN EMP_I1 进一步讲,如果sql语句中对索引列进行排序,因为索引已经预先排序好了,所以在执行计划中不需要再对索引列进行排序 SQL> explain plan for select empno, ename from emp where empno > 7876 order by empno; Query Plan --- SELECT STATEMENT [CHOOSE...
· 事务控制(commit, rollback) SQL 语句的执行过程(SQL Statement Execution) 图3-1 概要的列出了处理和运行一个sql语句的需要各个重要阶段。在某些情况下,Oracle运行sql的过程可能与下面列出的各个阶段的顺序有所不同。如DEFINE阶段可能在FETCH阶段之前,这主要依赖你如何书写代码。 对许多oracle的工具来说,其中某些...
One frequent “gotcha” in SQL is trying to use a where statement to filter aggregations, which will violate SQL order of execution rules. This is because when the where statement is being evaluated, the “group by” statement has yet to be executed and aggregate values are unknown. Thus, ...
| 0 | SELECT STATEMENT | | 19 | 1349 | 1 (100)| 00:00:01 | | 1 | SORT ORDER BY | | 19 | 1349 | 1 (100)| 00:00:01 | |* 2 | COUNT STOPKEY | | | | | | | 3 | FIXED TABLE FULL| X$BH | 19 | 1349 | 0 (0)| 00:00:01 | ...
"order_items": [ {"sushi_id": 1, "order_id": 1},{"sushi_id": 1, "order_id": ...
Overview of SQL Statement Execution Figure 5-1outlines the stages commonly used to process and execute a SQL statement. In some cases, these steps might be executed in a slightly different order. For example, theDEFINEstage could occur just before theFETCHstage, depending on how your code is ...
databricks api post /api/2.0/sql/statements/ \ --profile <profile-name> \ --json '{ "warehouse_id": "'"$DATABRICKS_SQL_WAREHOUSE_ID"'", "catalog": "samples", "schema": "tpch", "format": "ARROW_STREAM", "disposition": "EXTERNAL_LINKS", "statement": "SELECT l_orderkey, l_exten...
STATEMENT | | 19 | 1349 | 1 (100)| 00:00:01 | |* 1 | COUNT STOPKEY | | | | | | | 2 | VIEW | | 100 | 7100 | 1 (100)| 00:00:01 | |* 3 | SORT ORDER BY STOPKEY| | 100 | 7100 | 1 (100)| 00:00:01 | | 4 | FIXED TABLE FULL | X$BH | 100 | 7100 | 0...
Execution Plan --- 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=197 Card=1 Bytes=12) 1 0 SORT (AGGREGATE) 2 1 HASH JOIN (Cost=197 Card=400 Bytes=4800) 3 2 HASH JOIN (Cost=45 Card=100 Bytes=800) 4 3 TABLE ACCESS (FULL) OF 'T...