建议的方法连接多个列并用分隔符分隔?

我有一张像这样的桌子

ROW_ID, ID_A, ID_B, ID_C, ID_D
1001, A, NULL, NULL, NULL
1002, A, NULL, B, NULL
1003, NULL, B, NULL, NULL
1004, NULL, NULL, C, D

ROW_ID, ID_COMBINED
1001, "A"
1002, "A, B"
1003, "B"
1004, "C, D"

首先我设置查询,使初始表值是空字符串而不是空字符串,然后使用 CONCATENATE(A,', ', B,', ',C,', ',D) 方法,但这会给我这样的值:

ROW_ID, ID_COMBINED
1001, "A,,"
1002, "A,B,,"
1003, ",B,,"
1004, ",,C,D"

NULLIF() 但是,当我用空值合并列时,我会丢失具有如下重写的组合字符串方面:

ROW_ID, ID_COMBINED
1001, "A"
1002, "B"
1003, "B"
1004, "D"