--малек покурочил, чтобы почитабельнее
-- View: "information_schema.constraint_column_usage"
/*CREATE OR REPLACE VIEW information_schema.constraint_column_usage AS */
 SELECT current_database()::information_schema.sql_identifier AS table_catalog
, x.tblschema::information_schema.sql_identifier AS table_schema
, x.tblname::information_schema.sql_identifier AS table_name
, x.colname::information_schema.sql_identifier AS column_name
, current_database()::information_schema.sql_identifier AS constraint_catalog
, x.cstrschema::information_schema.sql_identifier AS constraint_schema
, x.cstrname::information_schema.sql_identifier AS constraint_name
/*йа*/, contype
   FROM (
/*( SELECT DISTINCT nr.nspname, r.relname, r.relowner, a.attname, nc.nspname, c.conname
           FROM pg_namespace nr, pg_class r, pg_attribute a, pg_depend d, pg_namespace nc, pg_constraint c
          WHERE nr.oid = r.relnamespace
		AND r.oid = a.attrelid
		AND d.refclassid = 'pg_class'::regclass::oid
		AND d.refobjid = r.oid 
		AND d.refobjsubid = a.attnum
		AND d.classid = 'pg_constraint'::regclass::oid
		AND d.objid = c.oid
		AND c.connamespace = nc.oid
		AND c.contype = 'c'::"char"
		AND r.relkind = 'r'::"char"
		AND NOT a.attisdropped
          ORDER BY nr.nspname, r.relname, r.relowner, a.attname, nc.nspname, c.conname)
	UNION ALL 
*/
         SELECT nr.nspname, r.relname, r.relowner, a.attname, nc.nspname, c.conname
/*йа*/,c.contype
           FROM pg_namespace nr, pg_class r, pg_attribute a, pg_namespace nc, pg_constraint c
          WHERE nr.oid = r.relnamespace
		AND r.oid = a.attrelid
		AND nc.oid = c.connamespace
		AND 
                CASE
                    WHEN c.contype = 'f'::"char" THEN r.oid = c.confrelid AND (a.attnum = ANY (c.confkey))
                    ELSE r.oid = c.conrelid AND (a.attnum = ANY (c.conkey))
                END
		AND NOT a.attisdropped
		AND (c.contype = ANY (ARRAY['p'::"char", 'u'::"char", 'f'::"char"])		)
		AND r.relkind = 'r'::"char"
/*1*/
)
 AS x(tblschema, tblname, tblowner, colname, cstrschema, cstrname
/*йа*/,contype)
 WHERE pg_has_role(x.tblowner, 'USAGE'::text)
/*йа*/ AND contype = 'f';

(a.attnum = ANY (c.confkey))
--по аналогии:
(a1.attnum = ANY (c1.conkey))