Question

I have a table called data:

create table data
(
   ID int primary key,
   val varchar(50),
   forID int

   constraint fk_forID foreign key (forID) references otherTable(forID)
)

I have a view called dataFrequencies

create view dataFrequencies (val, freq)
as select val, COUNT(*)
     from data
 group by val
 order by freq desc

What I want is the subset of rows from table data where val is in the top fifty rows of dataFrequencies.

My current solution is somewhat roundabout. I create a table topFifty that contains the top 50 rows of dataFrequencies. Then I create a view topFiftyVals which selects all from data but inner joins on table topFifty:

create table topFifty
(
   val varchar(50) primary key
)

insert into topFifty select val from dataFrequencies order by frequency desc limit 50;

create view topFiftyVals (ID, val, forID)
as select *
     from data d
inner join topFifty tf on d.val = tf.val

I am sure there is some kind of direct querying method that will do this! Thanks for all the help!

Answer 1

Yes, there is a direct way. It’s the code in your topFiftyVals view, slightly altered:

     select d.*, tf.freq
       from data d
 inner join ( select val, COUNT(*) AS freq
                from data
            group by val
            order by freq desc
               limit 50
            ) tf 
         on d.val = tf.val ;