const rows:5 filtered:1.00 Extra:Using index condition;Using where;Using filesort 1rowinset,1 warning (0.00 sec) # 执行用时 5 rows in set(0.01 sec) 其中: ・key_len: 160,表明联合索引的两个字段都用到了,(32+20) * 32 * 2 160。
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +---+---+---+---+---+---+---+---+---+---+ | 1 | PRIMARY | o | index | | PRIMARY | 8 | | 24 | Using where; Using temporary | | 2 | DEPENDENT SUBQUERY | |...
开窗函数over()包含三个分析子句:分组子句(partition by), 排序子句(order by), 窗口子句(rows) 窗口就是分析函数分析时要处理的数据范围,就拿sum来说,它是sum窗口中的记录而不是整个分组中的记录,因此我们在想得到某个栏位的累计值时,我们需要把窗口指定到该分组中的第一行数据到当前行, 如果你指定该窗口从...
数据库由若干张表(Table)组成,这里说的数据Table很像Excel里的表; 正如Excel里的表格,Table也是由行(rows)和列(columns)组成 一个Table存储一个类别的数据,每一行是一条数据,每一列是这种数据的一个属性; Table就像一个二维的表格,列(columns)是有限固定的,行(rows)是无限不固定的,如: 试水 1、movies为表名...
To create a negative condition, you can precede any of these conditional operators, except for ANY and ALL, with the NOT operator. 3.1:BETWEEN value-1 AND value-2 ( between or equal to 两端的value是被包括进去的) To select rows based on a range of numeric or character values(value可以使...
Find the total number of rows in theProductstable: SELECTCOUNT(*) FROMProducts; Try it Yourself » Syntax SELECTCOUNT(column_name) FROMtable_name WHEREcondition; Demo Database Below is a selection from theProductstable used in the examples: ...
┌─count()─┐ │678375│ └─────────┘ 1rowsinset. Elapsed:0.009sec. Processed1.38million rows,8.30MB(160.29million rows/s.,961.76MB/s.) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 使用标量子查询结果 WITH(
rows filtered Extra 1 SIMPLE e const PRIMARY PRIMARY 4 const 1 100 由于emp_id 是主键,执行计划显示通过主键索引(PRIMARY)进行查询。 另外,也可以通过一些图形工具或者数据库提供的其他方式查看 SQL 语句的执行计划。 89. 以下查询语句会不会使用索引? CREATE INDEX idx ON test (col); SELECT COUNT() FROM...
We typically use theCOUNT()function to count the number of rows in a result set. Often, we include a WHERE condition in the query to filter rows before performing the count. When we need to count the same column differently, we usually write multiple queries with different WHERE conditions....
with tmp as ( select id from test where score > 60 ) -- 使用临时表 select distinct id from tmp; group by/with rollup group by 主要是用来做数据聚合 需要选择字段作为聚合维度后,然后通过聚合函数得到汇总值的过程。 count,sum,avg,... max/min,std,variance,... rank,first/last_value,row_num...