使用 SELECT 查询将值传递给 LIMIT function

Question

There is a table named STATION.

I want to display rows of the table.

SELECT *
FROM STATION
LIMIT (SELECT COUNT(ID) FROM STATION)/2

I tried to perform a query like this but I am getting syntax error.

What is wrong in this query?

How can I perform this query?

Answer 1

One method is to use window functions:

select t.*
from (select t.*,
             ntile(2) over (order by id) as tile
      from t
     ) t
where tile = 1;

Answer 2

I have never seen a need of querying exactly half the table. If you are asking this out of curiosity, that's fair but if there is really a need where you are trying to implement something like this, please revisit the design.

Coming to your question, you can possibly do two things:

1. Implement a stored procedure and query the count and store in a variable and then pass it on to the actual SELECT query for the LIMIT clause.

2. From your client code fire 2 different queries - 1 for count and calculate half (non fraction) and then pass it to the limit clause of next select query.