问题
I\'m looking for something similar this in SQL Server:
SELECT TOP n WITH TIES FROM tablename
I know about LIMIT in PostgreSQL, but does the equivalent of the above exist? I\'m just curious as it would save an extra query each time for me.
If I have a table Numbers with attribute nums: {10, 9, 8, 8, 2}. I want to do something like:
SELECT nums FROM Numbers ORDER BY nums DESC LIMIT *with ties* 3
It should return {10, 9, 8, 8} because it takes the top 3 plus the extra 8 since it ties the other one.
回答1:
There is no WITH TIES clause in PostgreSQL like there is in SQL Server.
In PostgreSQL I would substitute this for TOP n WITH TIES .. ORDER BY <something>:
WITH cte AS (
SELECT *, rank() OVER (ORDER BY <something>) AS rnk
FROM tbl
)
SELECT *
FROM cte
WHERE rnk <= n;
To be clear, rank() is right, dense_rank() would be wrong (return too many rows).
Consider this quote from the SQL Server docs (from the link above):
For example, if expression is set to 5 but 2 additional rows match the values of the ORDER BY columns in row 5, the result set will contain 7 rows.
The job of WITH TIES is to include all peers of the last row in the top n as defined by the ORDER BY clause. rank() gives the exact same result.
To make sure, I tested with SQL server, here is a live demo.
And here is a more convenient SQLfiddle.
回答2:
Try this:
Output: 10, 9, 8, 8
with numbers (nums) as (
values (10), (9), (8), (8), (2)
)
SELECT nums FROM Numbers
WHERE nums in (SELECT DISTINCT nums FROM Numbers ORDER BY nums DESC LIMIT 3)
ORDER BY nums DESC
Output: 10,10,9,8,8
with numbers (nums) as (
values (10), (9), (8), (8), (2), (10)
)
SELECT nums FROM Numbers
WHERE nums in (SELECT DISTINCT nums FROM Numbers ORDER BY nums DESC LIMIT 3)
ORDER BY nums DESC
来源：https://stackoverflow.com/questions/9629953/postgresql-equivalent-for-top-n-with-ties-limit-with-ties