Retrieve Unique Values and Counts For Each

问题:

Is there a simple way to retrieve a list of all unique values in a column, along with how many times that value appeared?

Example dataset:

A
A
A
B
B
C

... Would return:

A  |  3
B  |  2
C  |  1

回答1:

Use GROUP BY:

select value, count(*) from table group by value

Use HAVING to further reduce the results, e.g. only values that occur more than 3 times:

select value, count(*) from table group by value having count(*) > 3

回答2:

SELECT id,COUNT(*) FROM file GROUP BY id