mysql5.7 with as

在MySQL 5.7中，WITH AS是一种使用通用表表达式（CTE）的方法。CTE是指在查询中创建临时结果集的一种方式，可以在查询中多次引用这个结果集，从而使复杂查询变得更加简洁和可读。使用WITH AS，您可以将一个或多个CTE定义为已命名的临时表，并在接下来的查询中使用它们。

以下是使用WITH AS在MySQL 5.7中创建临时表的示例：

WITH
cte1 AS (
SELECT id, end_time, status
FROM t_wl_record_repairs_detail
WHERE end_time IS NULL
),
cte2 AS (
SELECT COUNT(1) as sum, 'today' as name
FROM cte1
)
SELECT * FROM cte2;

在上面的示例中，cte1定义了一个临时表，其中包含满足条件的记录。然后，cte2使用cte1并计算了记录的数量，并添加了一个名为"today"的列。

相关问题

mysql 5.7的with as

引用:mysql专业须知教程 学习mysql的100 页教程 mySQL是一个开源关系数据库管理系统 (RDBMS)，由 Oracle 公司开发和支持。 它是一本非官方且免费的 MySQL 电子书，用于教育目的。。

引用:原来是与磁盘临时表有关。在MySQL 5.7版本中，内部磁盘临时表的默认引擎是InnoDB引擎，这就意味着当SELECT操作需要在磁盘上创建临时表时(例如GROUP BY操作)，就会使用到InnoDB引擎。。

引用:Finally, I figured out that I was focusing on the wrong queries. I was trying to correlate the spikes on the InnoDB Rows inserted graph to the DML queries (writes). However, the spike was caused by SELECT queries! But why would SELECT queries cause the massive InnoDB insert operation? How is this even possible?

"with as"是一种在MySQL 5.7中引入的语法，它用于创建临时视图。通过使用"with as"语法，可以在查询中定义一个或多个临时视图，然后在同一个查询中使用这些临时视图进行其他操作。

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.