Four fundamental questions on Sequences

Question

DB version:11G
Question *1* and *2*:
To determine the current value of a Sequence i try
SQL> SELECT  SEQ_SHP_HDR.CURRVAL FROM DUAL;
SELECT  SEQ_SHP_HDR.CURRVAL FROM DUAL
ERROR at line 1:
ORA-08002: sequence SEQ_SHP_HDR.CURRVAL is not yet defined in this
sessionI know that if i use
SELECT  SEQ_SHP_HDR.NEXTVAL FROM DUAL;i can get CURRVAL from the sequence. But that will increment the sequence.
So I tried looking at user_sequences.last_number . But user_sequences.last_number was showing 552 when the actual currval was 545 !
Why am i getting the above error (SEQ_SHP_HDR.CURRVAL is not yet defined in this session) and how can one accurately determine
the currval of a sequence without incrementing it using NEXTVAL?
Question *3*.
To Increment a sequence, one should use
alter sequence <sequencename> increment by n ;Right?
Do you guys use
SELECT  <sequencename>.NEXTVAL FROM DUAL;to increment SEQUENCES?
Question *4*.
I was trying to increment a sequence. After the ALTER statement, the sequence didn't get incremented. I had to issue a NEXTVAL call to actually get this reflected. Why is this happening?
SQL> select * from v$version where rownum=1;
BANNER
Oracle Database 11g Release 11.1.0.7.0 - 64bit Production
SQL> CREATE SEQUENCE myseq
  2    START WITH 1
  3    NOMAXVALUE;
Sequence created.
SQL> select myseq.nextval from dual;
   NEXTVAL
         1
SQL> alter sequence myseq increment by 7;
Sequence altered.
SQL> select myseq.currval from dual;
   CURRVAL
         1
SQL> select myseq.nextval from dual;
   NEXTVAL
         8
SQL> select myseq.currval from dual;
   CURRVAL
         8
        

Answer 1

Steve_74 wrote:
DB version:11G
Question *1* and *2*:
To determine the current value of a Sequence i try
SQL> SELECT  SEQ_SHP_HDR.CURRVAL FROM DUAL;
SELECT  SEQ_SHP_HDR.CURRVAL FROM DUAL
ERROR at line 1:
ORA-08002: sequence SEQ_SHP_HDR.CURRVAL is not yet defined in this
sessionI know that if i use
SELECT  SEQ_SHP_HDR.NEXTVAL FROM DUAL;i can get CURRVAL from the sequence. But that will increment the sequence.
So I tried looking at user_sequences.last_number . But user_sequences.last_number was showing 552 when the actual currval was 545 !
Why am i getting the above error (SEQ_SHP_HDR.CURRVAL is not yet defined in this session) and how can one accurately determine
the currval of a sequence without incrementing it using NEXTVAL?You cant get the CURRVAL unless you execute the NEXTVAL alteast once in your session. And you cant use the user_sequences.last_number if the CACHE is enabled.
Question *3*.
To Increment a sequence, one should use
alter sequence <sequencename> increment by n ;Right?WRONG!! You have actually altered the structure of your sequence. With ALTER comand you are actually setting the increment value. Here "n" sets the increment size. If set as 1 it will increment by 1. If set as 2 will increment by 2.
Do you guys use
SELECT  <sequencename>.NEXTVAL FROM DUAL;to increment SEQUENCES?YES that is the correct way to increment a sequence. Use NEXTVAL to increment a sequence.
Question *4*.
I was trying to increment a sequence. After the ALTER statement, the sequence didn't get incremented. I had to issue a NEXTVAL call to actually get this reflected. Why is this happening?
SQL> select * from v$version where rownum=1;
BANNER
Oracle Database 11g Release 11.1.0.7.0 - 64bit Production
SQL> CREATE SEQUENCE myseq
2    START WITH 1
3    NOMAXVALUE;
Sequence created.
SQL> select myseq.nextval from dual;
NEXTVAL
1
SQL> alter sequence myseq increment by 7;
Sequence altered.
SQL> select myseq.currval from dual;
CURRVAL
1
SQL> select myseq.nextval from dual;
NEXTVAL
8
SQL> select myseq.currval from dual;
CURRVAL
8
Answer for the question 3 answers this one as well!!