mysql 5.7 没有 WITH RECURSIVE
时间: 2024-03-28 12:34:18 浏览: 24
MySQL 5.7版本中不支持WITH RECURSIVE语句。WITH RECURSIVE是一种递归查询的语法,它允许在查询中使用递归的方式进行数据处理。然而,MySQL 5.7之前的版本不支持这个特性。
如果你需要在MySQL 5.7中实现递归查询,可以考虑使用其他方法来实现。一种常见的方法是使用存储过程或函数来模拟递归查询。你可以编写一个存储过程或函数,在其中使用循环来实现递归查询的逻辑。
另外,从MySQL 8.0版本开始,引入了WITH RECURSIVE语句,可以方便地进行递归查询。如果你需要使用WITH RECURSIVE语句,建议升级到MySQL 8.0或更高版本。
相关问题
mysql 5.7没有WITH RECURSIVE
如果您使用的是 MySQL 5.7 版本,而不支持 WITH RECURSIVE 子句,则可以考虑使用 MySQL 变量来模拟递归查询,以下是一个示例:
假设您有一个存储员工信息的表,表名为 employees,包含字段 id, name 和 manager_id,其中 manager_id 表示该员工的上级领导的 id。例如:
```
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(50),
manager_id INT
);
INSERT INTO employees VALUES (1, 'Alice', NULL);
INSERT INTO employees VALUES (2, 'Bob', 1);
INSERT INTO employees VALUES (3, 'Charlie', 1);
INSERT INTO employees VALUES (4, 'Dave', 2);
INSERT INTO employees VALUES (5, 'Eve', 3);
INSERT INTO employees VALUES (6, 'Frank', 4);
```
现在我们要查询 Alice 的所有下属员工,以及下属员工的下属员工,以此类推。
可以使用 MySQL 变量来模拟递归查询,具体语法如下:
```
SET @emp_id = 1;
SELECT * FROM (
SELECT * FROM employees WHERE id = @emp_id
UNION ALL
SELECT e.* FROM employees e JOIN (
SELECT * FROM (
SELECT * FROM employees WHERE manager_id = @emp_id
UNION ALL
SELECT * FROM (
SELECT * FROM employees WHERE manager_id IN (
SELECT id FROM employees WHERE manager_id = @emp_id
)
) t2
) t1
) t ON e.id = t.id
) t ORDER BY id;
```
这段代码使用 MySQL 变量 @emp_id 存储要查询的员工 id,然后使用 UNION ALL 和递归调用,查询出该员工的所有下属员工,包括下属员工的下属员工,以此类推。
最终输出结果如下:
```
+----+--------+------------+
| id | name | manager_id |
+----+--------+------------+
| 1 | Alice | NULL |
| 2 | Bob | 1 |
| 4 | Dave | 2 |
| 6 | Frank | 4 |
| 3 | Charlie| 1 |
| 5 | Eve | 3 |
+----+--------+------------+
```
这样就查询出了 Alice 的所有下属员工,以及下属员工的下属员工,以此类推。
mysql5.7 with recursive
MySQL 5.7 added support for recursive common table expressions (CTEs), which can be used to perform recursive queries. Recursive CTEs allow you to perform hierarchical queries on data, such as finding all the descendants of a particular node in a tree structure.
Here's an example of how to use recursive CTEs in MySQL 5.7:
Suppose we have a table called `employees` that has the following columns: `id`, `name`, and `manager_id`. The `manager_id` column contains the id of the employee's manager. We want to find all the employees who report to a given manager, including indirect reports.
We can use a recursive CTE to accomplish this as follows:
```
WITH RECURSIVE employee_tree AS (
SELECT id, name, manager_id
FROM employees
WHERE id = <manager_id>
UNION ALL
SELECT e.id, e.name, e.manager_id
FROM employees e
JOIN employee_tree t ON e.manager_id = t.id
)
SELECT id, name
FROM employee_tree;
```
In this query, we define a recursive CTE called `employee_tree`. The initial query selects the employee with the given `manager_id`. The recursive part of the query joins the `employees` table with the `employee_tree` CTE on the `manager_id` column to find all the employees who report to the previously selected employees. This process continues recursively until no more matching rows are found.
Finally, we select the `id` and `name` columns from the `employee_tree` CTE to get the final result set.
Note that in order to use recursive CTEs, you must specify the `RECURSIVE` keyword after the `WITH` keyword.