PostgresQL 中有没有rownum这样的，显示结果集的序号?

在Oracle里面rownum可以用来标示行号, 如 : 
SQL> select rownum,table_name from dba_tables where rownum<10;

    ROWNUM TABLE_NAME
---------- ------------------------------
         1 ICOL$
         2 CON$
         3 UNDO$
         4 PROXY_ROLE_DATA$
         5 FILE$
         6 UET$
         7 IND$
         8 SEG$
         9 COL$

9 rows selected.
PostgreSQL使用窗口函数row_number()可以满足同样的需求
postgres=# select * from (select row_number() over() as rownum,tablename from pg_tables) t where rownum<10;
 rownum |    tablename    
--------+-----------------
      1 | pg_statistic
      2 | pg_type
      3 | pg_attribute
      4 | pg_authid
      5 | pg_proc
      6 | pg_class
      7 | pg_database
      8 | pg_user_mapping
      9 | pg_constraint
(9 rows)