GROUP BY 和 DISTINCT 之間的區別

GROUP BY 與聚合函式結合使用。請考慮下表：

下面的查詢使用 GROUP BY 執行聚合計算。

SELECT
    storeName,
    COUNT(*) AS total_nr_orders,
    COUNT(DISTINCT userId) AS nr_unique_customers,
    AVG(orderValue) AS average_order_value,
    MIN(orderDate) AS first_order,
    MAX(orderDate) AS lastOrder
FROM
    orders
GROUP BY
    storeName;

並將返回以下資訊

雖然 DISTINCT 用於列出指定列的不同值的唯一組合。

SELECT DISTINCT
    storeName,
    userId
FROM
    orders;