postgreSQL外鍵引用查詢 查詢外鍵被那些表占用

根據一個表名，查詢所有外鍵引用它的表，以及那些外鍵的列名
key_column_usage（系統列信息表），
pg_constraint（系統所有約束表）

SELECT  x.table_name,
        x.column_name
  FROM  information_schema.key_column_usage x
  INNER JOIN  (SELECT  t.relname, 
                       a.conname 
                 FROM  pg_constraint a 
                 INNER JOIN pg_class ft
                         ON ft.oid = a.confrelid 
                 INNER JOIN pg_class t 
                         ON t.oid = a.conrelid
                WHERE  a.contype = 'f' 
                  AND  a.confrelid =
                       (select e.oid 
                          from pg_class e
                         where e.relname = 'xxx_table')
                ) tp 
          ON (x.table_name = tp.relname AND
              x.constraint_name = tp.conname)