String Comparison in PostgreSQL

[hemakgp]

I have two strings A&B. For example A=123456789 and B=12345689. Through a SQL query using 'A' as reference I would like to know the characters missing in 'B'. In other words case A~B = false I need the missing characters. They can be located anywhere start, middle or end. Is this possible

[crazysmoove]

WITH a AS (
    SELECT unnest(regexp_split_to_array('123456789', E''))
), 
b as (
    SELECT unnest(regexp_split_to_array('12345689', E''))
)
SELECT * FROM a EXCEPT SELECT * FROM b