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2024年4月14日发(作者：matlab filter design)
mysql5.7递归查询语句
英文回答：
To perform a recursive query in MySQL 5.7, you can use
a common table expression (CTE) along with the UNION
operator. Here's an example to illustrate the process:
Let's say we have a table called "employees" with
columns "id" and "manager_id". The "manager_id" column
contains the ID of the employee's manager. We want to
retrieve all the employees who report directly or
indirectly to a specific manager.
First, we need to define the initial query that
retrieves the direct reports of the given manager. We can
use a CTE for this:
WITH RECURSIVE employee_hierarchy AS (。
SELECT id, manager_id.
FROM employees.
WHERE manager_id = 1 -Assuming we want to find the
employees reporting to manager with ID 1。
UNION.
SELECT , r_id.
FROM employees e.
INNER JOIN employee_hierarchy eh ON r_id =
.
)。
SELECT FROM employee_hierarchy;
In this example, the initial query selects the
employees who directly report to the manager with ID 1. The
UNION operator is used to combine this result with the
recursive part of the query.
The recursive part of the query joins the "employees"
table with the CTE "employee_hierarchy" on the condition
that the employee's manager ID matches the ID from the CTE.
This allows us to retrieve the employees who indirectly
report to the given manager.
Finally, we select all the rows from the CTE
"employee_hierarchy" to get the desired result.
中文回答：
在MySQL 5.7中执行递归查询，可以使用公共表表达式（CTE）
以及UNION操作符。下面是一个示例来说明整个过程：
假设我们有一个名为"employees"的表，包含"ID"和
"manager_id"两个列。"manager_id"列包含员工的经理的ID。我们
想要检索所有直接或间接报告给特定经理的员工。
首先，我们需要定义初始查询，用于检索给定经理的直接下属。
我们可以使用CTE来实现：
WITH RECURSIVE employee_hierarchy AS (。
SELECT id, manager_id.
FROM employees.
WHERE manager_id = 1 -假设我们要查找报告给ID为1的经
理的员工。
UNION.
SELECT , r_id.
FROM employees e.
INNER JOIN employee_hierarchy eh ON r_id =
.
)。
SELECT FROM employee_hierarchy;
在这个例子中，初始查询选择直接报告给ID为1的经理的员工。
UNION操作符用于将该结果与递归查询的部分组合起来。
递归查询的部分将"employees"表与CTE
"employee_hierarchy"根据员工的经理ID与CTE中的ID进行连接。
这样我们就可以检索间接报告给给定经理的员工。
最后，我们从CTE "employee_hierarchy"中选择所有行来获取
所需的结果。
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