Sql postgres 9.6的合并和case-when语句

我正在尝试回填一些数据。这个表中的A列可能来自于multiples表，我可以使用coalesce函数。如果coalesce返回null，那么我需要转到另一个表，根据该表中的值，我需要向该列插入一个硬编码的值

Backfill Table - T1
Backfill Column - Column A

Coalesce Tables - TC2, TC3, TC4, TC5,TC6
Coalesce Columns - TC2.C2, TC3.C3, TC4.C4, TC5.C5,TC6.C6

Another Table - AT1
Another Column - CAT1

If CAT1 = 21, then Column A should be 100
If CAT1 = 22, then Column A should be 200
If CAT1 = 23, then Column A should be 300
If CAT1 = 24, then Column A should be 400

假设有多个柱需要回填，此处未显示

INSERT INTO TABLE T1 (COLUMN A)
SELECT
coalesce (TC2.C2, TC3.C3, TC4.C4, TC5.C5,TC6.C6),
',
',
'
FROM A JOIN TC2 blah blah;

我只是不知道如何包含AT1表的条件或案例语句

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编辑：我问的是合并语句中的case语句

你的问题不清楚。。试着添加一个合适的数据样本和导出的结果。我想这就是我想要的。谢谢

INSERT INTO TABLE T1 (COLUMN A)
    CASE 
        WHEN (SELECT coalesce (TC2.C2, TC3.C3, TC4.C4, TC5.C5,TC6.C6)) IS NOT NULL
        THEN  (SELECT coalesce (TC2.C2, TC3.C3, TC4.C4, TC5.C5,TC6.C6))
        WHEN AT1.CAT1 = '21' THEN '100'
        WHEN AT1.CAT1 = '22' THEN '200'
        WHEN AT1.CAT1 = '23' THEN '300'
        WHEN AT1.CAT1 = '24' THEN '400'
    END AS NEW_COLUMN_VALUE