Query grants for a table in postgres

How can I query all GRANTS granted to an object in postgres?

For example I have table "mytable":

GRANT SELECT, INSERT ON mytable TO user1
GRANT UPDATE ON mytable TO user2 

I need somthing which gives me:

user1: SELECT, INSERT
user2: UPDATE

I already found it:

SELECT grantee, privilege_type 
FROM information_schema.role_table_grants 
WHERE table_name='mytable'

\z mytable from psql gives you all the grants from a table, but you'd then have to split it up by individual user.

The query below will give you a list of all users and their permissions on the table in a schema.

select a.schemaname, a.tablename, b.usename,
  HAS_TABLE_PRIVILEGE(usename, quote_ident(schemaname) || '.' || quote_ident(tablename), 'select') as has_select,
  HAS_TABLE_PRIVILEGE(usename, quote_ident(schemaname) || '.' || quote_ident(tablename), 'insert') as has_insert,
  HAS_TABLE_PRIVILEGE(usename, quote_ident(schemaname) || '.' || quote_ident(tablename), 'update') as has_update,
  HAS_TABLE_PRIVILEGE(usename, quote_ident(schemaname) || '.' || quote_ident(tablename), 'delete') as has_delete, 
  HAS_TABLE_PRIVILEGE(usename, quote_ident(schemaname) || '.' || quote_ident(tablename), 'references') as has_references 
from pg_tables a, pg_user b 
where a.schemaname = 'your_schema_name' and a.tablename='your_table_name';

More details on has_table_privilages can be found here.

If you really want one line per user, you can group by grantee (require PG9+ for string_agg)

SELECT grantee, string_agg(privilege_type, ', ') AS privileges
FROM information_schema.role_table_grants 
WHERE table_name='mytable'   
GROUP BY grantee;

This should output something like :

 grantee |   privileges   
---------+----------------
 user1   | INSERT, SELECT
 user2   | UPDATE
(2 rows)

This query will list all of the tables in all of the databases and schemas (uncomment the line(s) in the WHERE clause to filter for specific databases, schemas, or tables), with the privileges shown in order so that it's easy to see if a specific privilege is granted or not:

SELECT grantee
      ,table_catalog
      ,table_schema
      ,table_name
      ,string_agg(privilege_type, ', ' ORDER BY privilege_type) AS privileges
FROM information_schema.role_table_grants 
WHERE grantee != 'postgres' 
--  and table_catalog = 'somedatabase' /* uncomment line to filter database */
--  and table_schema  = 'someschema'   /* uncomment line to filter schema  */
--  and table_name    = 'sometable'    /* uncomment line to filter table  */
GROUP BY 1, 2, 3, 4;

Sample output:

grantee |table_catalog   |table_schema  |table_name     |privileges     |
--------|----------------|--------------|---------------|---------------|
PUBLIC  |adventure_works |pg_catalog    |pg_sequence    |SELECT         |
PUBLIC  |adventure_works |pg_catalog    |pg_sequences   |SELECT         |
PUBLIC  |adventure_works |pg_catalog    |pg_settings    |SELECT, UPDATE |
...

Adding on to @shruti's answer

To query grants for all tables in a schema for a given user

select a.tablename, 
       b.usename, 
       HAS_TABLE_PRIVILEGE(usename,tablename, 'select') as select,
       HAS_TABLE_PRIVILEGE(usename,tablename, 'insert') as insert, 
       HAS_TABLE_PRIVILEGE(usename,tablename, 'update') as update, 
       HAS_TABLE_PRIVILEGE(usename,tablename, 'delete') as delete, 
       HAS_TABLE_PRIVILEGE(usename,tablename, 'references') as references 
from pg_tables a, 
     pg_user b 
where schemaname='your_schema_name' 
      and b.usename='your_user_name' 
order by tablename;

Here is a script which generates grant queries for a particular table. It omits owner's privileges.

SELECT 
    format (
      'GRANT %s ON TABLE %I.%I TO %I%s;',
      string_agg(tg.privilege_type, ', '),
      tg.table_schema,
      tg.table_name,
      tg.grantee,
      CASE
        WHEN tg.is_grantable = 'YES' 
        THEN ' WITH GRANT OPTION' 
        ELSE '' 
      END
    )
  FROM information_schema.role_table_grants tg
  JOIN pg_tables t ON t.schemaname = tg.table_schema AND t.tablename = tg.table_name
  WHERE
    tg.table_schema = 'myschema' AND
    tg.table_name='mytable' AND
    t.tableowner <> tg.grantee
  GROUP BY tg.table_schema, tg.table_name, tg.grantee, tg.is_grantable;