数据库高级查询sql语句实例
    ## Advanced SQL Queries for Database Manipulation.
    ### Subqueries.
    Subqueries are nested queries that are used within the WHERE, HAVING, or FROM clauses of a main query. They allow for complex filtering and data retrieval.
    Example:
    sql.
    SELECT.
    FROM users.
    WHERE id IN (SELECT id FROM orders WHERE product_id = 10);
    This query retrieves all users who have placed an order for product ID 10.
    ### Joins.
    Joins combine data from multiple tables by matching rows based on common columns. Different types of joins include inner joins, outer joins, cross joins, and self joins.
    Example:
    sql.
    SELECT.
    FROM users u.
数据库应用案例    INNER JOIN orders o ON u.id = o.user_id;
    This query retrieves all users and their corresponding orders.
    ### Window Functions.
    Window functions perform calculations across a set of rows within a window frame. They
are used for aggregation, ranking, and moving calculations.
    Example:
    sql.
    SELECT ,。
        SUM(price) OVER (PARTITION BY product_id) AS total_price.
    FROM orders;
    This query calculates the total price for each product.
    ### Common Table Expressions (CTEs)。
    CTEs are temporary tables that can be defined within a query. They are useful for complex data transformations and reducing code duplication.
    Example:
    sql.
    WITH temp_table AS (。
        SELECT product_id, SUM(quantity) AS total_quantity.
        FROM orders.
        GROUP BY product_id.
    )。
    SELECT.
    FROM temp_table.
    WHERE total_quantity > 10;
    This query retrieves all products with a total quantity greater than 10.

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