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SQL语句中SELECT是开发或者数据分析中经常要用的，如何写出一个好的SELECT语句，其首要条件就是要知道SELECT的执行顺序，这样才可以更好的为SELECT语句做优化。

SQL的基本结构

一个常见的SELECT SQL结构如下：

SELECT
[ALL | DISTINCT | DISTINCTROW ]
[HIGH_PRIORITY]
[STRAIGHT_JOIN]
[SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
select_expr [, select_expr] ...
[into_option]
[FROM table_references
[PARTITION partition_list]]
[WHERE where_condition]
[GROUP BY {col_name | expr | position}, ... [WITH ROLLUP]]
[HAVING where_condition]
[WINDOW window_name AS (window_spec)
[, window_name AS (window_spec)] ...]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[into_option]
[FOR {UPDATE | SHARE}
[OF tbl_name [, tbl_name] ...]
[NOWAIT | SKIP LOCKED]
| LOCK IN SHARE MODE]
[into_option]

SELECT执行顺序

以下步骤显示SELECT语句的逻辑处理顺序或绑定顺序。

1.FROM
2.ON
3.JOIN
4.WHERE
5.GROUP BY
6.WITH CUBE or WITH ROLLUP
7.HAVING
8.SELECT
9.DISTINCT
10.ORDER BY
11.TOP