如何在SQL中比较多列？实现多列相等判断并生成计算列

你的SQL语句存在语法逻辑错误：SQL不支持ReqUntilReleased= ReqUntilReadyReleased = ReqUntilDelivery = ReqUntilResolved这种连续相等的写法。这种表达式会先计算ReqUntilReleased=ReqUntilReadyReleased得到布尔值（0或1，依SQL方言而定），再将该布尔值与ReqUntilDelivery比较，最后再和ReqUntilResolved比较，完全达不到判断四个字段值全部相等的目的。

下面是两种正确的实现方式：

方法一：使用AND连接逐字段比较 #

SELECT 
    IssueID,
    ReqUntilReleased,
    ReqUntilReadyReleased,
    ReqUntilDelivery,
    ReqUntilResolved,
    CASE 
        WHEN ReqUntilReleased = ReqUntilReadyReleased 
             AND ReqUntilReadyReleased = ReqUntilDelivery 
             AND ReqUntilDelivery = ReqUntilResolved
        THEN CAST(ReqUntilResolved AS VARCHAR(10))  -- 转换为字符串，保证与ELSE返回类型一致
        ELSE 'Invalid'
    END AS Cumulative
FROM Table1;

方法二：利用行内聚合判断唯一值数量 #

如果你的SQL支持VALUES行构造器，可以通过统计四个字段的唯一值数量是否为1来判断：

SELECT 
    IssueID,
    ReqUntilReleased,
    ReqUntilReadyReleased,
    ReqUntilDelivery,
    ReqUntilResolved,
    CASE 
        WHEN (SELECT COUNT(DISTINCT val) 
              FROM (VALUES (ReqUntilReleased), 
                           (ReqUntilReadyReleased), 
                           (ReqUntilDelivery), 
                           (ReqUntilResolved)) AS t(val)) = 1
        THEN CAST(ReqUntilResolved AS VARCHAR(10))
        ELSE 'Invalid'
    END AS Cumulative
FROM Table1;

针对你提供数据的示例结果（假设ReqUntilDelivery字段值与其他字段匹配逻辑一致）： #

内容的提问来源于stack exchange，提问作者Fatemeh