Re: PostgreSQL equivalent of Oracle "member of"

Vadi schrieb am 29.03.2019 um 10:44:
> I would like to know if there is any equivalent in PostgreSQL for the Oracle "member of" syntax.
>
> The usage is as shown below:
>
> I have used the Oracle sample HR schema for the below example:
>
> CREATE OR REPLACE TYPE params as table of varchar2 (100);
> /
>
> CREATE OR REPLACE function in_list (in_list in varchar2) return params pipelined as
> param_list varchar2(4000) := in_list || ',';
> pos number;
> begin
> loop
> pos := instr(param_list, ',');
> exit when nvl(pos, 0) = 0;
> pipe row (trim(substr(param_list, 1, pos - 1)));
> param_list := substr(param_list, pos + 1);
> end loop;
>
> return;
> end in_list;
> /
>
> CREATE TABLE tname as
> SELECT listagg(first_name, ', ') within group (order by first_name) first_name FROM employees;
>
> SELECT * FROM tname;
>
> SELECT * FROM employees
> WHERE first_name member of in_list(first_name);

I don't understand where the parameter to the in_list() functions comes from in the last query.
As written it would be the value from employees.first_name, which is not a comma separated list, so it doesn't really make sense.

I think what the in_list() function does, would be the equivalent to unnest/string_to_array

e.g.:

select *
from unnest(string_to_array('foo,bar', ',')) as t(name);

returns

name
----
foo
bar

If you just want to check if one string is contained in a comma separated list, you can use the ANY operator:

where first_name = any (string_to_array('foo,bar', ','))

Thomas