数据库中两个字段的 SQL

你能得到一个数据库表中两个不同字段的不同组合吗？如果是，您能否提供 SQL 示例。

sql
distinct

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最佳答案

How about simply:

select distinct c1, c2 from t

select c1, c2, count(*)
from t
group by c1, c2

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If you want distinct values from only two fields, plus return other fields with them, then the other fields must have some kind of aggregation on them (sum, min, max, etc.), and the two columns you want distinct must appear in the group by clause. Otherwise, it's just as Decker says.

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If you still want to group only by one column (as I wanted) you can nest the query:

select c1, count(*) from (select distinct c1, c2 from t) group by c1

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You can get result distinct by two columns use below SQL:

SELECT COUNT(*) FROM (SELECT DISTINCT c1, c2 FROM [TableEntity]) TE

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Share my stupid thought:

Maybe I can select distinct only on c1 but not on c2, so the syntax may be select ([distinct] col)+ where distinct is a qualifier for each column.

But after thought, I find that distinct on only one column is nonsense. Take the following relationship:

   | A | B
__________
1| 1 | 2
2| 1 | 1

If we select (distinct A), B, then what is the proper B for A = 1?

Thus, distinct is a qualifier for a statement.