SQL 选择列..如果为 NULL，则选择其他列

Question

我有这样的看法：

ID| Key | Product | Item | Block | Source | Title | Text | Type | H1 | H2 | H3 |
-------------------------------------------------------------------------------
1 | 456 | abcd    | def  |  1    |  TP    | QWERT | YUIP | tgr  | A1 | A2 | A3 |
2 | 567 | fhrh    | klo  |  1    |  GT    | TREWQ | ITGF | trp  | A1 | A2 | A3 |
3 | 891 | ufheu   | yut  |  2    |  FR    | WERTY | MNBV | uip  |NULL|NULL|NULL|

我想将其中一些列导出到现有的空表中。我想选择前六列，然后选择其他列，就像从右到左的层次结构一样。

如果 H1、H2 和 H3 不为空，则它们应出现在输出中，并且标题、文本和类型应为 NULL（即使它们包含值）。

如果 H1、H2 和 H3 为 NULL，我希望标题、文本和类型出现在输出中。

它应该是这样的：

ID| Key | Product | Item | Block | Source | Title | Text | Type | H1 | H2 | H3 |
-------------------------------------------------------------------------------
1 | 456 | abcd    | def  |  1    |  TP    | NULL  | NULL | NULL | A1 | A2 | A3 |
2 | 567 | fhrh    | klo  |  1    |  GT    | NULL  | NULL | NULL | A1 | A2 | A3 |
3 | 891 | ufheu   | yut  |  2    |  FR    | WERTY | MNBV | uip  |NULL|NULL|NULL|

有人能帮我解决这个问题吗？非常感谢您的帮助！

Answer 1

如果您想要逐列比较，请使用coalesce()：

select ID, Key, Product, Item, Block, Source,
       (case when h1 is not null then null else title end) as title,
       (case when h2 is not null then null else text end) as text,
       (case when h3 is not null then null else type end) as type,
       coalesce(h1, title) as h1,
       coalesce(h2, text) as h2,
       coalesce(h3, type) as h3
from t;

但是，我不确定您是否同时指所有三列：

select ID, Key, Product, Item, Block, Source,
       (case when h1 is null and h2 is null and h3 is null then title end) as title,
       (case when h1 is null and h2 is null and h3 is null then text end) as text,
       (case when h1 is null and h2 is null and h3 is null then type end) as type,
       (case when h1 is null and h2 is null and h3 is null then NULL else h1 end) as h1,
       (case when h1 is null and h2 is null and h3 is null then NULL else h2 end) as h2,
       (case when h1 is null and h2 is null and h3 is null then NULL else h3 end) as h3
from t;