MySQL CTE (Common Table Expressions)示例全解析

WITH cte_name AS (
    SELECT ...  -- CTE查询定义
)
SELECT * FROM cte_name;  -- 主查询

WITH department_stats AS (
    SELECT 
        department_id, 
        COUNT(*) as employee_count,
        AVG(salary) as avg_salary
    FROM employees
    GROUP BY department_id
)
SELECT 
    d.department_name,
    ds.employee_count,
    ds.avg_salary
FROM departments d
JOIN department_stats ds ON d.department_id = ds.department_id;

WITH 
high_earners AS (
    SELECT * FROM employees WHERE salary > 100000
),
it_employees AS (
    SELECT * FROM employees WHERE department_id = 10
)
SELECT 
    h.employee_id,
    h.name,
    'High Earner' as category
FROM high_earners h
UNION ALL
SELECT 
    i.employee_id,
    i.name,
    'IT Employee' as category
FROM it_employees i;

WITH RECURSIVE cte_name AS (
    -- 基础部分（种子查询）
    SELECT ... WHERE ...
    UNION [ALL]
    -- 递归部分
    SELECT ... FROM cte_name JOIN ...
    WHERE ...
)
SELECT * FROM cte_name;

WITH RECURSIVE org_hierarchy AS (
    -- 基础部分：查找顶级管理者
    SELECT 
        employee_id,
        name,
        manager_id,
        1 as level
    FROM employees
    WHERE manager_id IS NULL
    UNION ALL
    -- 递归部分：查找下属员工
    SELECT 
        e.employee_id,
        e.name,
        e.manager_id,
        oh.level + 1
    FROM employees e
    JOIN org_hierarchy oh ON e.manager_id = oh.employee_id
)
SELECT * FROM org_hierarchy ORDER BY level, employee_id;

WITH RECURSIVE number_sequence AS (
    SELECT 1 AS n
    UNION ALL
    SELECT n + 1 FROM number_sequence WHERE n < 10
)
SELECT * FROM number_sequence;

WITH 
monthly_sales AS (
    SELECT 
        DATE_FORMAT(order_date, '%Y-%m') as month,
        SUM(amount) as total_sales
    FROM orders
    GROUP BY month
),
growth_rate AS (
    SELECT 
        month,
        total_sales,
        LAG(total_sales) OVER (ORDER BY month) as prev_sales,
        (total_sales - LAG(total_sales) OVER (ORDER BY month)) / 
        LAG(total_sales) OVER (ORDER BY month) * 100 as growth_pct
    FROM monthly_sales
)
SELECT * FROM growth_rate;

WITH 
raw_data AS (
    SELECT * FROM source_table WHERE quality_check = 1
),
cleaned_data AS (
    SELECT 
        id,
        TRIM(name) as name,
        CASE WHEN age < 0 THEN NULL ELSE age END as age
    FROM raw_data
)
SELECT * FROM cleaned_data;

WITH RECURSIVE path_finder AS (
    SELECT 
        start_node as path,
        start_node,
        end_node,
        1 as length
    FROM graph
    WHERE start_node = 'A'
    UNION ALL
    SELECT 
        CONCAT(pf.path, '->', g.end_node),
        g.start_node,
        g.end_node,
        pf.length + 1
    FROM graph g
    JOIN path_finder pf ON g.start_node = pf.end_node
    WHERE FIND_IN_SET(g.end_node, REPLACE(pf.path, '->', ',')) = 0
)
SELECT * FROM path_finder;

SET SESSION cte_max_recursion_depth = 2000;

WITH cte_name AS (
    SELECT /*+ MERGE() */ * FROM table_name
)
SELECT * FROM cte_name;