在SQL中选择每第n条具有条件的行

Question

This seems a conceptually easy question, but with no straightforward answer.

I have some time-serious data, with a whole bunch (millions) of unique events given by the event_ID variable, describing a set (of several) physical properties (phys_props).

I'm writing SQL and want to return every nth row (where I have freedom to choose n to be eg 5, 1000, 10000 etc.) for this time-series dataset.

However, if eg n=1000 and there are less than 1000 records for a given physical property, I don't want to return the event_ID records there at all.

Something like:

SELECT * 
FROM myTable
WHERE MOD(myTable, 1000) = 0 

is my starting point.

Answer 1

you can give an unique no to each of the row, and then do the calculation on the unique no. Something like this

with t as(    
select *,row_number() over (order by event_ID) SN from the_table_name
)

select * from t where SN%100=0

Answer 2

You can try something like this:

SELECT * FROM 
(SELECT EVENT_ID,  
       @rownum := @rownum + 1 AS rank
FROM myTable, 
       (SELECT @rownum := 0) r
) ds
WHERE MOD(rank, 5) = 0
;

Answer 3

You can try this:

         Select * from myTable
         Having mod(count(*), 1000)=0