基础语法及执行顺序
查询语句语法
1 | SELECT [ALL | DISTINCT] select_expr, select_expr, ... |
书写次序和执行次序
顺序 | 书写次序 | 书写次序说明 | 执行次序 | 执行次序说明 |
---|---|---|---|---|
1 | select |
查询 | from |
先执行表与表直接的关系 |
2 | from |
先执行表与表直接的关系 | on |
|
3 | join on |
join |
||
4 | where |
where |
过滤 | |
5 | group by |
分组 | group by |
分组 |
6 | having |
分组后再过滤 | having |
分组后再过滤 |
7 | distribute by cluster by |
4个by | select |
查询 |
8 | sort by |
distinct |
去重 | |
9 | order by |
distribute by cluster by |
4个by | |
10 | limit |
限制输出的行数 | sort by |
|
11 | union/union all |
合并 | order by |
|
12 | limit |
限制输出的行数 | ||
13 | union /union all |
合并 |