Question

尝试将变量设置为字符串时，我在语法错误中运行。该字符串在IF/ELSE语句中构造，该语句将基于字段为null的形式提供消息的变体。我在SELECT行之后的set @errorMsg上收到语法错误。然后将在另一个查询中调用该变量。此时，我不确定查询是否有问题，或者我是否看错了。

declare @errorMsg nvarchar(MAX)
declare @combinedString VARCHAR(MAX)

IF EXISTS (select y from db.b)
    BEGIN
    set @errorMsg =
        SELECT @combinedString = COALESCE(@combinedString + ', ', '') + x_y
        from (select CONCAT(cg.x, '-', f.y) AS x_y
        from db.a cg
        LEFT JOIN db.b f
        ON cg.x = f.y) AS w
        SELECT 'The x listed in the database are (x - y if applicable): ' + @combinedString as StringValue
    END
ELSE
    BEGIN
    set @errorMsg =
        SELECT @combinedString = COALESCE(@combinedString + ', ', '') + x_y
        from (select cg.x AS x_y
        from db.a) AS w
        SELECT 'The x listed in the database are (x - y if applicable): ' + @combinedString as StringValue
    END

Answer 1

在查询时，“ SET @errorMsg”可能位于错误的位置。

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使用包含SELECT语句的IF / ELSE设置变量

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