T-SQL UPDATE在PRINT之前缓慢​​，快速

Question

我试图从名单和电子邮件地址列表中删除重复项。我的脚本的最后一个声明是一个更新，它需要的时间比它应该的长 - 我从未真正等待它完成。如果我放置PRINT＆＃39;任何东西＆＃39 ;;直接在它前面的声明，它立即返回。有或没有WHILE（）循环的情况相同。

这是一个简化版本，我希望能够说明这个问题。我实际上正在制作一个表值函数，所以我不能将PRINT留在那里。 PRINT可能会产生什么影响？

SQL Server 10.50.4033（2008 R2）

DECLARE @duplicate_names TABLE (
    dnDuplicateKey int,
    dnPrimaryKey int,
    PRIMARY KEY (
        dnPrimaryKey,
        dnDuplicateKey
    )
);

DECLARE @matches TABLE (
    mFirstKey int,
    mSecondKey int,
    PRIMARY KEY (
        mFirstKey,
        mSecondKey
    )
);

--Find Email matches
INSERT INTO @matches
SELECT DISTINCT
    f.elKey,
    s.elKey
FROM
    Emails f INNER JOIN
        Emails s
    ON f.elEMail = s.elEMail;

--Find name matches
INSERT INTO @matches
SELECT
    f.NameKey,
    s.NameKey
FROM
    Names f INNER JOIN
        Names s
    ON f.Name = s.Name
WHERE
    NOT EXISTS (
        SELECT
            *
        FROM
            @Matches
        WHERE
            mFirstKey = f.NameKey
            AND mSecondKey = s.NameKey
    )

--Condense duplicate matches
--  1 = 2,
--  2 = 1,
--  3 = 4,
--  4 = 3
--to
--  1 = 2,
--  3 = 4
INSERT INTO @duplicate_names
SELECT
    mSecondKey,
    MIN(mFirstKey)
FROM
    @matches
GROUP BY
    mSecondKey;

--Condense chained matches
--  1 = 2,
--  2 = 3,
--  3 = 4
--to
--  1 = 2,
--  1 = 3,
--  1 = 4
WHILE(@@ROWCOUNT > 0)
    UPDATE
        d
    SET
        d.dnPrimaryKey = f.dnPrimaryKey
    FROM
        @duplicate_names d INNER JOIN (
            @duplicate_names f INNER JOIN
                @duplicate_names s
            ON f.dnDuplicateKey = s.dnPrimaryKey
        ) ON d.dnDuplicateKey = s.dnDuplicateKey
    WHERE
        d.dnPrimaryKey <> f.dnPrimaryKey;

Answer 1

所以是的，这只是表变量和临时表之间的性能差异。对于感兴趣的人，这是我如何在不使用临时表的情况下解决它。它仍然比第一种方法慢，但由于我不能在表值函数中使用临时表，所以它是我看到的唯一选项。

DECLARE @duplicate_names TABLE (
    dnDuplicateKey int,
    dnPrimaryKey int,
    PRIMARY KEY (
        dnPrimaryKey,
        dnDuplicateKey
    )
);

DECLARE @matches TABLE (
    mFirstKey int,
    mSecondKey int,
    PRIMARY KEY (
        mFirstKey,
        mSecondKey
    )
);

--Find Email matches
INSERT INTO @matches
SELECT DISTINCT
    f.elKey,
    s.elKey
FROM
    Emails f INNER JOIN
        Emails s
    ON f.elEMail = s.elEMail;

--Find name matches
INSERT INTO @matches
SELECT
    f.NameKey,
    s.NameKey
FROM
    Names f INNER JOIN
        Names s
    ON f.Name = s.Name
WHERE
    NOT EXISTS (
        SELECT
            *
        FROM
            @matches
        WHERE
            mFirstKey = f.NameKey
            AND mSecondKey = s.NameKey
    );

--Expand orphaned matches (for which no reciprocal version exists).
WHILE(@@ROWCOUNT > 0)
    INSERT INTO @matches
    SELECT DISTINCT
        f.mFirstKey,
        s.mSecondKey
    FROM
        @matches f INNER JOIN
            @matches s
        ON f.mSecondKey = s.mFirstKey
    WHERE
        s.mSecondKey <> f.mFirstKey
        AND NOT EXISTS (
            SELECT
                *
            FROM
                @matches d
            WHERE
                d.mFirstKey = f.mFirstKey
                AND d.mSecondKey = s.mSecondKey
        );

--Condense duplicate matches
--  1 = 2,
--  2 = 1,
--  3 = 4,
--  4 = 3
--to
--  1 = 2,
--  3 = 4
INSERT INTO @duplicate_names
SELECT
    mSecondKey,
    MIN(mFirstKey)
FROM
    @matches
GROUP BY
    mSecondKey;