mysql limit rows returned for each group -

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i have result in table

+------------------------------------------------+ |adm_no   |   code     | value   |   group_id    | +------------------------------------------------+ |1200     |  101       | 50      |    1          | +------------------------------------------------+ |1200     |   102      | 60      |    1          | +------------------------------------------------+ |1200     |  121       | 62      |    1          | +------------------------------------------------+ |1200     |  233       |  50     |   2           | +------------------------------------------------+ |1200     |  231       |  98     |   2           | +------------------------------------------------+ |1200     |  232       | 85      |    2          | +------------------------------------------------+ |1200     | 511        |   75    |     3         | +------------------------------------------------+ |1200     |  585       |   38    |     3         | +------------------------------------------------+ |1200     |  711       |    45   |      4        | +------------------------------------------------+ |1200     |   785      |     45  |      4        | +------------------------------------------------+

now can select limited set of rows each group long number limit same dont know how this.

so want this:

1.select rows have group_id=1

2.select first 2 rows have group_id=2

3.select first row have group_id=3 , group_id=4

any pointers possibly if can done in single query

you can using variables:

select adm_no, code, value, group_id (   select adm_no, code, value, group_id,          @rn := if (@gr = group_id,                     if(@gr := group_id, @rn+1, @rn+1),                     if(@gr := group_id, 1, 1)) rn   mytable   cross join (select @rn:=0, @gr:=0) vars   order group_id, code ) t (group_id = 1)        or (group_id = 2 , rn <= 2)        or (group_id in (3,4) , rn = 1)

variables @rn, @gr used implement row_number() on (partition ..) window function available in other rdbmss sql server, postgresql, etc...

so, @rn used enumerate records within each group_id slice. using variable in outer query can expected result set.

please note use of nested conditionals, in order consume , then set @gr variable.

demo here


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