How is sql with used?

The WITH statement is a syntax structure in SQL that is used to create temporary views or tables which can be referenced directly in subsequent queries.

The general syntax of a WITH statement is as follows:

WITH [临时视图名] AS (
    SELECT [字段列表]
    FROM [表名]
    WHERE [条件]
    GROUP BY [分组字段]
    HAVING [分组条件]
    ORDER BY [排序字段]
)
SELECT [查询字段]
FROM [临时视图名]
WHERE [条件]
GROUP BY [分组字段]
HAVING [分组条件]
ORDER BY [排序字段]

The specific usage of the WITH statement is as follows:

1. Define a temporary view or temporary table after the WITH statement, which can be used to retrieve data using subqueries or JOIN operations.
2. Filtering, grouping, sorting, and other operations can be performed on temporary views or tables to obtain the desired results.
3. In the SELECT statement following the WITH clause, you can reference fields from temporary views or temporary tables to perform further querying or analysis operations.

Using the WITH statement can simplify complex SQL queries, improve query efficiency, and also make SQL code easier to read and maintain.