MySQL 查询执行流程，SQL解析顺序

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SQL示例：

SELECT DISTINCT
    < select_list >
FROM
    < left_table > < join_type >
JOIN < right_table > ON < join_condition >
WHERE
    < where_condition >
GROUP BY
    < group_by_list >
HAVING
    < having_condition >
ORDER BY
    < order_by_condition >
LIMIT < limit_number >

执行顺序：

FROM <left_table>
ON <join_condition>
<join_type> JOIN <right_table>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
SELECT 
DISTINCT <select_list>
ORDER BY <order_by_condition>
LIMIT <limit_number>

乍一看SQL的解析执行顺序还是让我有点儿出乎意料。但仔细看发现还是很合理的

从哪些表获取数据，这些表中数据通过哪个字段对应，检索什么样的数据，如何进行分组，过滤组，选择排重数据，然后再进行排序限制取几条。