Limit rows with distinct

[livius...@poczta.onet.pl]

Hi

i am curious if

1. 

SELECT

DISTINCT X.NAME

FROM

TABLE_X X

ROWS 2

is equal to

2. 

SELECT

Y.NAME

FROM

(

SELECT

DISTINCT X.NAME

FROM

TABLE_X X

) Y

ROWS 2

or maybe it is

3.

SELECT

DISTINCT Y.NAME

FROM

(

SELECT

X.NAME

FROM

TABLE_X X

ROWS 2

) Y

And is it always one of these cases, regardless of the query plan?

I’m fairly sure the answer is “2,” but I need to be certain.

To make the question a bit more complex, consider different LIMIT-style clauses:

a) rows:

SELECT

DISTINCT X.NAME

FROM

TABLE_X X

ROWS 2

b) first:

SELECT

FIRST 2 DISTINCT X.NAME

FROM

TABLE_X X

c)  fetch:

SELECT

DISTINCT X.NAME

FROM

TABLE_X X

FETCH FIRST 2 ROWS ONLY

regards,

Karol Bieniaszewski

[Vlad Khorsun]

  Rows limit applied to the final result set, i.e. after sorting and/or grouping.

Regards,

Vlad