What do numbers mean in SQL ORDER/GROUP BY statements? -


i don't understand sql sub-query , doubts it:

  1. what purpose of numbers after "group by" , "order by" keyword i.e. group 1,2,3 or order 1,2

subquery:

select a.dep_month,          a.dep_day_of_week,    avg(a.flight_distance) average_distance ( select dep_month,              dep_day_of_week,              dep_date,              sum(distance) flight_distance     flights     group 1,2,3 )   group 1,2  order 1,2;

thanks in advance :)

well, order 1, 2 means order 1st , 2nd fields in select, 

    select a.dep_month,            a.dep_day_of_week,       ...   order 1,2;

is equal to

    select a.dep_month,            a.dep_day_of_week,        ...   order a.dep_month, a.dep_day_of_week;

the syntax can convenient if have long , complex expression in field:

    select bla-bla-bla-...-bla-bla,            ...   order 1 -- no copy + paste of "bla-bla-bla-...-bla-bla"

a better approach, however, put alias

    select bla-bla-bla-...-bla-bla myexpression,            ...   order myexpression -- more readable 1

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