Operator does not exist: character varying = character varying[]

Question

As you can see in my SQL request I have a subquery which returns string array ( varchar[] ). I am trying to filter table_1 values by this array which I pass in ANY command. For some reason I see this error:

ERROR: operator does not exist: character varying = character varying[] No operator matches the given name and argument types. You might need to add explicit type casts.

The data types of table_1.colomn_a and table_2.colomn_a columns are varchar .

PostgreSQL version: 11.4

Where did I make a mistake?

select
    table_1.*
from
    table_1
where
    table_1.colomn_a = any(
        select
            array_agg(table_2.colomn_a)
        from
            table_2
    )

Of course, I can use such code, but I want to know the reason for the error in the first query:

select
    table_1.*
from
    table_1
where
    table_1.colomn_a in(
        select
            table_2.colomn_a
        from
            table_2
    )

Answer 1

Your subquery:

select
    array_agg(table_2.colomn_a)
from
    table_2

returns an array of an array of varchar, not an array of varchar. So you are trying to compare a varchar ( table_1.colomn_a ) with an array of varchar ( array_agg(table_2.colomn_a) ), which is not possible. Consider if your subquery had an explicit group by clause eg

select
    array_agg(table_2.colomn_a)
from
    table_2
group by table_2.colomn_b

In this case it's obvious that the query returns an array of arrays of varchar (one for each table_2.colomn_b value). In your first query, there is an implicit group by clause, which results in the output being an array of an array of varchar. You can just use:

select
    table_2.colomn_a
from
    table_2

and it will work fine (in this case = any is equivalent to in ).

Answer 2

You already have an array. So use exists :

where exists (select 1
              from table_2 t2
              where table_1.colomn_a = any(t2.colomn_a)
             )

No need to bring the arrays together into a bigger array, just to parse that array to look for another value.