如何制作 STRING_AGG 的 DISTINCT答案

【问题标题】：how to make a DISTINCT of STRING_AGG如何制作 STRING_AGG 的 DISTINCT
【发布时间】：2021-12-26 21:46:06
【问题描述】：

我正在尝试对 STRING_AGG 函数的 offerDetails 列进行 DISTINCT

OUTER APPLY
(
    SELECT 
        STRING_AGG(CAST(co.OfferId AS NVARCHAR(MAX)), ';') AS OfferDetails, 
        STRING_AGG(CAST(ct.ConferenceId AS NVARCHAR(MAX)), ';') AS CustomTransferDetails
    FROM ConferenceTransfer ct
    INNER JOIN ConferenceOffer co ON ct.ConferenceId = co.ConferenceId
    WHERE
        ct.ConferenceTransferTypeId = 1 AND
        ct.DateStarted IS NOT NULL AND
        ct.CallerUserId = @agentId AND
        ct.DateInitiated BETWEEN @dateFrom AND @dateTo
) CallTransfered

【问题讨论】：

修复架构！如果您在单个列中分隔数据，您应该将您的架构视为BROKEN。这是一个有缺陷的设计，需要额外的桌子。纠正他损坏的设计，突然间这个查询（可能还有其他查询）会更加简单。

标签： sql sql-server distinct

【解决方案1】：

我不知道任何使 string_agg 不同的本机方式，但您可以通过使用子查询和 row_number 来识别第一个实例，即忽略每个值的第一个实例，即

OUTER APPLY
(
    SELECT 
        STRING_AGG(CAST(CASE WHEN c.RowNumber = 1 THEN c.OfferId END AS NVARCHAR(MAX)), ';') AS OfferDetails, 
        STRING_AGG(CAST(c.ConferenceId AS NVARCHAR(MAX)), ';') AS CustomTransferDetails
    FROM (  SELECT  co.OfferId,
                    ct.ConferenceId,
                    RowNumber = ROW_NUMBER() OVER(PARTITION BY co.OfferId ORDER BY ct.ConferenceId)
            FROM    ConferenceTransfer ct
                    INNER JOIN ConferenceOffer co 
                        ON ct.ConferenceId = co.ConferenceId
            WHERE
                ct.ConferenceTransferTypeId = 1 AND
                ct.DateStarted IS NOT NULL AND
                ct.CallerUserId = @agentId AND
                ct.DateInitiated BETWEEN @dateFrom AND @dateTo
            ) AS c
) CallTransfered

关键部分是CASE WHEN c.RowNumber = 1 THEN c.OfferId END，所以除了第一个实例之外，您传递的是NULL，因此最终结果将只包含每个OfferId一次。

【讨论】：

【解决方案2】：

你需要按OfferId分组，然后再分组

OUTER APPLY
(
    SELECT 
        STRING_AGG(CAST(c.OfferId AS NVARCHAR(MAX)), ';') AS OfferDetails, 
        STRING_AGG(c.CustomTransferDetails, ';') AS CustomTransferDetails
    FROM (
        SELECT
            co.OfferId,
            STRING_AGG(CAST(ct.ConferenceId AS NVARCHAR(MAX)), ';') AS CustomTransferDetails
        FROM ConferenceTransfer ct
        INNER JOIN ConferenceOffer co ON ct.ConferenceId = co.ConferenceId
        WHERE
            ct.ConferenceTransferTypeId = 1 AND
            ct.DateStarted IS NOT NULL AND
            ct.CallerUserId = @agentId AND
            ct.DateInitiated BETWEEN @dateFrom AND @dateTo
        GROUP BY
            co.OfferId
    ) c
) CallTransfered

这显然只适用于一个DISTINCT。如果您需要两者都不同，您可以重新拆分值，区分它们并重新聚合

OUTER APPLY
(
    SELECT 
        (
            SELECT
                STRING_AGG(s.value, ';')
            FROM (
                SELECT DISTINCT s.value
                FROM STRING_SPLIT(OfferDetails, ';') s
            ) s
        ) AS OfferDetails, 
        (
            SELECT
                STRING_AGG(s.value, ';')
            FROM (
                SELECT DISTINCT s.value
                FROM STRING_SPLIT(ConferenceId, ';') s
            ) s
        ) AS CustomTransferDetails
    FROM (
        SELECT
            STRING_AGG(CAST(co.OfferId AS NVARCHAR(MAX)), ';') AS OfferDetails, 
            STRING_AGG(CAST(ct.ConferenceId AS NVARCHAR(MAX)), ';') AS CustomTransferDetails
        FROM ConferenceTransfer ct
        INNER JOIN ConferenceOffer co ON ct.ConferenceId = co.ConferenceId
        WHERE
            ct.ConferenceTransferTypeId = 1 AND
            ct.DateStarted IS NOT NULL AND
            ct.CallerUserId = @agentId AND
            ct.DateInitiated BETWEEN @dateFrom AND @dateTo
        GROUP BY
            co.OfferId
    ) c
) CallTransfered

【讨论】：