37

I am getting error for below query. Basically to use || & distinct together.

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

It works fine like this

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

& this

select string_agg(distinct user.col, 'post')
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3 Answers 3

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62 
select string_agg(distinct 'pre' || user.col, 'post')

As the above will deny the use of an index in the distinct aggregation take the 'pre' out

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

This would prepend a single "pre" string to the entire string_agg output, eg preFIRSTpostSECONDpostTHIRDpost. The original question (although not very clear) appears to request prepending "pre" to each item included within the aggregation, eg preFIRSTpostpreSECONDpostpreTHIRDpost.
4

The concat function can help you. 

select string_agg(distinct concat('pre',user.col, 'post'), '')
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3 
array_to_string(array_agg(distinct column_name::text), '; ')

Will get the job done

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