SQL 查询将多条记录中的值组合到单个列中

Posted 2023-04-19

【中文标题】SQL 查询将多条记录中的值组合到单个列中

【英文标题】：SQL Query to combine values from multiple records into a single column

【发布时间】：2018-06-21 17:12:50

【问题描述】：

在我的表格中，每条记录最多可以有 30 个不同的预算代码。 我需要一个将表中的所有预算代码作为单列返回的查询。 查询我有错误指出子查询返回的值超过 1 个。

SELECT 
        (SELECT [budgetCode1] FROM TABLE_NAME),
        (SELECT [budgetCode2] FROM TABLE_NAME),
        (SELECT [budgetCode3] FROM TABLE_NAME),
        (SELECT [budgetCode4] FROM TABLE_NAME),
        (SELECT [budgetCode5] FROM TABLE_NAME),
        (SELECT [budgetCode6] FROM TABLE_NAME),
        (SELECT [budgetCode7] FROM TABLE_NAME),
        (SELECT [budgetCode8] FROM TABLE_NAME),
        (SELECT [budgetCode9] FROM TABLE_NAME),
        (SELECT [budgetCode10] FROM TABLE_NAME),
        (SELECT [budgetCode11] FROM TABLE_NAME),
        (SELECT [budgetCode12] FROM TABLE_NAME),
        (SELECT [budgetCode13] FROM TABLE_NAME),
        (SELECT [budgetCode14] FROM TABLE_NAME),
        (SELECT [budgetCode15] FROM TABLE_NAME),
        (SELECT [budgetCode16] FROM TABLE_NAME),
        (SELECT [budgetCode17] FROM TABLE_NAME),
        (SELECT [budgetCode18] FROM TABLE_NAME),
        (SELECT [budgetCode19] FROM TABLE_NAME),
        (SELECT [budgetCode20] FROM TABLE_NAME),
        (SELECT [budgetCode21] FROM TABLE_NAME),
        (SELECT [budgetCode22] FROM TABLE_NAME),
        (SELECT [budgetCode23] FROM TABLE_NAME),
        (SELECT [budgetCode24] FROM TABLE_NAME),
        (SELECT [budgetCode25] FROM TABLE_NAME),
        (SELECT [budgetCode26] FROM TABLE_NAME),
        (SELECT [budgetCode27] FROM TABLE_NAME),
        (SELECT [budgetCode28] FROM TABLE_NAME),
        (SELECT [budgetCode29] FROM TABLE_NAME),
        (SELECT [budgetCode30] FROM TABLE_NAME) AS BudgetCodes
  FROM TABLE_NAME

【问题讨论】：

重新考虑您的宽数据库表，因为这是低效的存储并且无法正确扩展。创建一个 BudgetCodes 表，其中包含指向 TableName 的外键链接，并为 1-30 和 one 列维护 one 列指示符对应数字或字符串值的指示符。

正如@RolandmysqlDBA 的concluded：没有替代品或创可贴可以弥补糟糕的设计。请，为了您将来的理智，今天规范化该表！！！

我非常想规范化我的表格。不幸的是，这个表是通过另一个系统的数据转储创建的。我对表结构没有发言权。

【参考方案1】：

您的查询将返回 30 列，如果 TABLE_NAME 有多个记录，则会出错。相反，您想在此处使用 UNION 查询：

    SELECT [budgetCode1] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode2] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode3] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode4] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode5] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode6] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode7] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode8] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode9] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode10] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode11] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode12] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode13] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode14] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode15] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode16] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode17] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode18] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode19] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode20] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode21] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode22] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode23] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode24] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode25] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode26] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode27] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode28] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode29] FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode30] FROM TABLE_NAME

您还可以添加从哪个budgetcode 列派生的：

    SELECT [budgetCode1],"budgetCode1" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode2],"budgetCode2" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode3],"budgetCode3" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode4],"budgetCode4" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode5],"budgetCode5" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode6],"budgetCode6" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode7],"budgetCode7" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode8],"budgetCode8" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode9],"budgetCode9" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode10],"budgetCode10" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode11],"budgetCode11" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode12],"budgetCode12" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode13],"budgetCode13" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode14],"budgetCode14" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode15],"budgetCode15" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode16],"budgetCode16" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode17],"budgetCode17" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode18],"budgetCode18" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode19],"budgetCode19" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode20],"budgetCode20" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode21],"budgetCode21" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode22],"budgetCode22" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode23],"budgetCode23" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode24],"budgetCode24" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode25],"budgetCode25" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode26],"budgetCode26" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode27],"budgetCode27" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode28],"budgetCode28" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode29],"budgetCode29" as budgetcode FROM TABLE_NAME
    UNION ALL
    SELECT [budgetCode30],"budgetCode30" as budgetcode FROM TABLE_NAME AS BudgetCodes
FROM TABLE_NAME

【讨论】：

我们 SQL 人员需要强调这样的次优数据库设计，这会导致繁琐、复杂的查询！

@Parfait 完全同意。为每个预算代码设置列是一个糟糕的选择，并且会导致一些讨厌的（和缓慢的）联合查询以将其置于正确的格式（就像我们在这里所做的那样）。糟糕。

能否修改此查询以排除 NULL 或空字符串值？

您必须将其包装在子查询中并添加 WHERE 子句 WHERE [budgetcode1] IS NULL 或.. 将 WHERE 子句添加到每个单独的 SELECT 语句中。