SQL行到列？

SELECT
    SUM(CASE WHEN status = 'Pending' THEN 1 ELSE 0 END) AS Pending,
    SUM(CASE WHEN status = 'Completed' THEN 1 ELSE 0 END) AS Completed,
    SUM(CASE WHEN status = 'Cancelled' THEN 1 ELSE 0 END) AS Cancelled
FROM
    orders;

SELECT *
FROM
    (SELECT category, amount
     FROM sales) AS src
PIVOT
    (SUM(amount)
     FOR category IN ([Electronics], [Clothing], [Books])) AS piv;

SELECT
    e1.role AS Role,
    COUNT(e2.employee_id) AS Count
FROM
    employees e1
LEFT JOIN
    employees e2 ON e1.role = e2.role
GROUP BY
    e1.role;