SQL count(*) and distinct

Question

Why can't we use `count(distinct *)` in SQL? As in to count all distinct rows?

Accepted Answer

```
select count(*) from (select distinct * from MyTable) as T
```

Although I strongly suggest that you re-think any queries that use `DISTINCT`. In a large percentage of cases, `GROUP BY` is more appropriate (and faster).

EDIT: Having read the question comments, I should point out that you should never ask the DBMS to do more work than actually needs doing to get a result. If you know in advance that there will not be any duplicated rows in a table, then don't use `DISTINCT`.

SQL count(*) and distinct

Solution

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