Operator does not exist: json = json

Question

when I try to select some record from a table

    SELECT * FROM movie_test WHERE tags = (\'[\"dramatic\",\"women\", \"political\"]\'::json)

Answer 1

You cannot compare json values. You can compare text values instead:

SELECT * 
FROM movie_test 
WHERE tags::text = '["dramatic","women","political"]'

Note however that values of type json are stored as text in a format in which they are given. Thus the result of comparison depends on whether you consistently apply the same format:

SELECT 
    '["dramatic" ,"women", "political"]'::json::text =  
    '["dramatic","women","political"]'::json::text      -- yields false!

In Postgres 9.4+ you can solve this problem using type jsonb, which is stored in a decomposed binary format. Values of this type can be compared:

SELECT 
    '["dramatic" ,"women", "political"]'::jsonb =  
    '["dramatic","women","political"]'::jsonb           -- yields true

so this query is much more reliable:

SELECT * 
FROM movie_test 
WHERE tags::jsonb = '["dramatic","women","political"]'::jsonb

Read more about JSON Types.