Postgresql:Generate Sequence

Question

The query below generates a line of DNA sequence

prepare dna_length(int) as
with t1 as (select chr(65) as s union select chr(67) union select chr(71) union select         


        

Answer 1

Having worked with DNA content databases for quite some, and the scientists, that like to play with them (sequences that is), I recommend a slight extension to the query by @GordonLinoff. Hide your implementation behind a function which takes 2 parameters: the length of the sequence and the number of sequences desired. You can then get any (reasonable) sequence length and any (reasonable) number of them.

create or replace 
function dna_sequence(
         sequence_length     integer
        ,number_of_sequences integer default 1 )
 returns table (dna_strand text) 
 language sql
as $$ 
   select string_agg((array['A', 'C', 'G', 'T'])[1 + trunc(random() * 4)], '') 
     from generate_series(1, sequence_length , 1) gsn(n)  
    cross join generate_series(1, number_of_sequences, 1) gsx(x)
    group by x    
$$;

-- test
select *
  from dna_sequence(20,10) ;

select *
  from dna_sequence(250) ;
 
select *
  from dna_sequence(20,100) 
 where position ('AAA' in dna_strand) > 0; 

NOTE: The query in the above function is quite literally copy/paste Gordon Linoff's original. Then modified with only 2nd parameter changed in each generate series to the appropriate parameter value.