mysql count unique row values

问题

TABLE quotation

id  clientid
1   25
2   25
3   25
4   25
5   26

How can I query how many different clients exist in TABLE quotation? I don't want duplicate entries to be counted more than once.

I need the answer to be 2, in 1 row, because the only non-duplicated entries are (25, 26).

回答1:

select count(distinct clientid) from quotation

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回答2:

I tried the following on a MySQL 5.x database.

id is an integer and clientid is an integer. I populated with two rows:

id  clientid
1   25
2   25

This SQL query will print the rows that have exactly 2 elements:

select * from test1 group by clientid having count(*) = 2;

If you want 2 or more elements, replace = 2 in the example above with >= 2.

select * from test1 group by clientid having count(*) >= 2;

回答3:

I find a way out

SELECT COUNT(*) as total FROM (SELECT COUNT(*) FROM quotation GROUP BY
clientid) t1

回答4:

If you want to count the total number of unique entries this will return a number in column count.

SELECT COUNT(*) as total FROM (SELECT COUNT(*) FROM quotation GROUP BY clientid having count(*) > 1) t1

If you want to count the total number of entries with duplicate rows then use the following mysql.

SELECT COUNT(*) as total FROM (SELECT COUNT(*) FROM quotation GROUP BY clientid having count(*) >= 2) t1

回答5:

SELECT clientid, COUNT(clientid) FROM quotation 
GROUP BY clientid

来源：https://stackoverflow.com/questions/4131937/mysql-count-unique-row-values