Issue with string_agg with non-postgres

Question

I get an error for the request below. Mostly use || and distinct together.

 select string_agg( 'pre' || distinct user.col, 'post') 

It works great, like this one.

 select string_agg( 'pre' || user.col, 'post') 

& this is

 select string_agg(distinct user.col, 'post') 

Answer 1

 select string_agg(distinct 'pre' || user.col, 'post') 

As stated above, using an index in distinct aggregation will result in 'pre' out

 select 'pre' || string_agg(distinct user.col, 'postpre') 

Answer 2

The concat function can help you.

 select string_agg(distinct concat('pre',user.col, 'post'), '')