时间：2021-01-10 11:07:51 | 栏目：Mysql | 点击：次
之前写过一篇 MySQL通过自定义函数的方式，递归查询树结构，从MySQL 8.0 开始终于支持了递归查询的语法
CTE
首先了解一下什么是 CTE，全名 Common Table Expressions
WITH cte1 AS (SELECT a, b FROM table1), cte2 AS (SELECT c, d FROM table2) SELECT b, d FROM cte1 JOIN cte2 WHERE cte1.a = cte2.c;
cte1, cte2 为我们定义的CTE，可以在当前查询中引用
可以看出 CTE 就是一个临时结果集，和派生表类似，二者的区别这里不细说，可以参考下MySQL开发文档：https://dev.mysql.com/doc/refman/8.0/en/with.html#common-table-expressions-recursive-examples
递归查询
先来看下递归查询的语法
WITH RECURSIVE cte_name AS ( SELECT ... -- return initial row set UNION ALL / UNION DISTINCT SELECT ... -- return additional row sets ) SELECT * FROM cte;
递归部分不能包括：
上面的讲解可能有点抽象，通过例子慢慢来理解
WITH RECURSIVE cte (n) AS -- 这里定义的n相当于结果集的列名，也可在下面查询中定义 ( SELECT 1 UNION ALL SELECT n + 1 FROM cte WHERE n < 5 ) SELECT * FROM cte; -- result +------+ | n | +------+ | 1 | | 2 | | 3 | | 4 | | 5 | +------+
EXAMPLE
最后来看一个树结构的例子
CREATE TABLE `c_tree` ( `id` int(11) NOT NULL AUTO_INCREMENT, `cname` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL, `parent_id` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
mysql> select * from c_tree; +----+---------+-----------+ | id | cname | parent_id | +----+---------+-----------+ | 1 | 1 | 0 | | 2 | 2 | 0 | | 3 | 3 | 0 | | 4 | 1-1 | 1 | | 5 | 1-2 | 1 | | 6 | 2-1 | 2 | | 7 | 2-2 | 2 | | 8 | 3-1 | 3 | | 9 | 3-1-1 | 8 | | 10 | 3-1-2 | 8 | | 11 | 3-1-1-1 | 9 | | 12 | 3-2 | 3 | +----+---------+-----------+
mysql> WITH RECURSIVE tree_cte as ( select * from c_tree where parent_id = 3 UNION ALL select t.* from c_tree t inner join tree_cte tcte on t.parent_id = tcte.id ) SELECT * FROM tree_cte; +----+---------+-----------+ | id | cname | parent_id | +----+---------+-----------+ | 8 | 3-1 | 3 | | 12 | 3-2 | 3 | | 9 | 3-1-1 | 8 | | 10 | 3-1-2 | 8 | | 11 | 3-1-1-1 | 9 | +----+---------+-----------+
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