使用 COALESCE 未在 SQL 服务器中给出预期的结果

Question

我有一个程序要生成一个由数组组成的类似 JSON 的字符串。

这是我正在使用的查询（以简单的脚本形式呈现）：

DECLARE @_l_All_Records_Str VARCHAR(MAX)
SELECT @_l_All_Records_Str = COALESCE(@_l_All_Records_Str , ',' , '') + '["' 
                                    + ISNULL(Time_Unit                  , ''  ) + '","'
                                    + ISNULL(CAST(Periods    AS VARCHAR), ''  ) + '","'
                                    + ISNULL(Details_Present            , 'N' ) + '","'     
                                    + ISNULL(Slice_1                    , ''  ) + '","'              
                                    + ISNULL(Slice_2                    , ''  ) + '","'              
                                    + ISNULL(Slice_3                    , ''  ) + '","'              
                                    + ISNULL(Slice_4                    , ''  ) + '","'              
                                    + ISNULL(Slice_5                    , ''  ) + '","'              
                                    + ISNULL(Slice_6                    , ''  ) + '","'              
                                    + ISNULL(Slice_7                    , ''  ) + '","'              
                                    + ISNULL(Slice_8                    , ''  ) + '","'              
                                    + ISNULL(Slice_9                    , ''  ) + '","'              
                                    + ISNULL(Slice_10                   , ''  ) + '","'              
                                    + ISNULL(Slice_11                   , ''  ) + '","'              
                                    + ISNULL(Slice_12                   , ''  ) + '"],'
 FROM MyTable ;

SET @_l_All_Records_Str = '[' + @_l_All_Records_Str + ']' ;

print @_l_All_Records_Str ;

结果几乎正确：

[,["M","1","N","Y","Y","Y","N","Y","Y","N","N","Y","Y","Y","N"],["D","","Y","Y","N","N","N","Y","N","N","N","N","N","N","N"],]

从结果中可以看出，有额外的 , 个字符（一个在开头，另一个在外部数组的末尾）。

有人可以建议我在这里遗漏了什么吗？

Answer 1

（代表问题作者发布答案。）

问题已解决！

输入错误：

COALESCE(@_l_All_Records_Str , ',' , '')

应该是：

COALESCE(@_l_All_Records_Str + ',' , '')

还有最后一个 , 需要删除（在 ...) + '"],' 中）。

使用 COALESCE 未在 SQL 服务器中给出预期的结果

Use of COALESCE not giving the desired result in SQL Server

sql-server

coalesce