对于并列的operator,上面的operator是树的左节点,优先执行。 mysql> explain format=tree select name from city where CountryCode in (select name from country where code like 'A%'); +---
This join type is like ref, but with the addition that MySQL does an extra search for rows that contain NULL values. This join type optimization is used most often in resolving subqueries. In the following examples, MySQL can use a ref_or_null join to process ref_table: 这个查询类型和ref...
The refcolumnshows which columnsorconstants are comparedtotheindexnamedinthekeycolumntoselectrowsfromthetable.Ifthe valueisfunc, the value usedisthe resultofsomefunction.Tosee whichfunction,useSHOW WARNINGS following EXPLAINto see the extended EXPLAIN output. Thefunctionmight actually be an operator such...
When theEXTENDED keyword is used, EXPLAIN produces extra information that can be viewedby issuing a SHOW WARNINGS statement following the EXPLAIN statement. Thisinformation displays how the optimizer qualifies table and column names in theSELECT statement, what the SELECT looks like after the applicatio...
When EXPLAIN is used with FOR CONNECTION connection_id rather than an explainable statement, it displays the execution plan for the statement executing in the named connection. See Section 8.8.4, “Obtaining Execution Plan Information for a Named Connection”. 当EXPLAIN与FOR CONNECTION connection_id...
range can be used when a key column is compared to a constant using any of the =, <>, >, >=, <, <=, IS NULL, <=>, BETWEEN, LIKE, or IN() operators: 通过索引范围查找多行数据,可以使用=, <>, >, >=, <, <=, IS NULL, <=>, BETWEEN, LIKE, 或 IN() 操作符。
在OceanBase 数据库中执行 update 向量形式的子查询时,使用 explain sql 命令解析语句时报错 4000。 示例如下。 创建测试表。 obclient> CREATE TABLE t1(c1 int, c2 int); Query OK, 0 rows affected (0.27 sec) obclient> CREATE TABLE t2(c1 int, c2 int); Query OK, 0 rows affected (0.23 sec) ...
索引范围扫描,常见于使用>,<,is null,between ,in ,like等运算符的查询中。 5.7 index 索引全表扫描,把索引从头到尾扫一遍,常见于使用索引列就能够处理不须要读取数据文件的查询、能够使用索引排序或者分组的查询。 5.8 ALL 这个就是全表扫描数据文件。然后再在server层进行过滤返回符合要求的记录。
In genere il più veloce algoritmo join di Amazon Redshift, escludendo altre considerazioni sui costi. AGGREGATION: Operatori e passaggi utilizzati per le query che coinvolgono funzioni aggregate e operazioni BY. GROUP Aggregazione aggr Operatore/Fase per le funzioni aggregate scalari. Hash...
SQL> explain plan for select * from emp where empno not in (select min(empno) from big_emp group by empno); Query Plan --- SELECT STATEMENT [CHOOSE] Cost=1 FILTER *** This is like a bounded nested loops TABLE ACCESS FULL EMP [...