Greenplum管理序列

不支持currval和lastval，只有nextval，且不能在update和delete语句中使用。如果开启了mirroring，序列不能在update和delete语句中使用。
gtlions=# create sequence sq1 start 1;
CREATE SEQUENCE
gtlions=# select * from sq1;
 sequence_name | last_value | increment_by |      max_value      | min_value | cache_value | log_cnt | is_cycled | is_called
---------------+------------+--------------+---------------------+-----------+-------------+---------+-----------+-----------
 sq1           |          1 |            1 | 9223372036854775807 |         1 |           1 |       1 | f         | f
(1 row)
gtlions=# select nextval('sq1');    
 nextval
---------
       1
(1 row)
gtlions=# insert into t1 values(nextval('sq1'),'a',19,date('2013-01-01'));
INSERT 0 1
gtlions=# insert into t1 values(nextval('sq1'),'a',19,date('2013-01-01'));
INSERT 0 1
gtlions=# alter sequence sq1 restart with 1;
ALTER SEQUENCE
gtlions=# select * from sq1;
 sequence_name | last_value | increment_by |      max_value      | min_value | cache_value | log_cnt | is_cycled | is_called
---------------+------------+--------------+---------------------+-----------+-------------+---------+-----------+-----------
 sq1           |          1 |            1 | 9223372036854775807 |         1 |           1 |       1 | f         | f

(1 row)

-EOF-