----- Original Message -----
Sent: 12 May 2006 22:47
Subject: Re: [Hsqldb-developers] Re:
Issue with SEQUENCE
Hello Fred:
Understanding SEQUENCES
Premise:
I have a simple table containing two fields:
CREATE TABLE SIMPLE(SEQ_ID INTEGER NOT NULL,NAME VARCHAR(100) NOT
NULL,CONSTRAINT SIMPLE_PK_1 PRIMARY KEY(SEQ_ID),CONSTRAINT SIMPLE_UK_1
UNIQUE(NAME))
I want the primary key of the table to be a sequence. So I define a
SEQUENCE
CREATE SEQUENCE SIMPLE_SEQ AS INTEGER START WITH 1
Now I want to Insert like so:
1. INSERT INTO SIMPLE VALUES ((CALL NEXT VALUE FOR
SIMPLE_SEQ),'Name1')
does not work.
2. INSERT INTO SIMPLE VALUES ((SELECT NEXT VALUE FOR SIMPLE_SEQ FROM
DUAL),'Name1')
works where DUAL is a table I created that has 1 record.
Is there a more elegant way of inserting the sequence without using the
DUAL table?
On 4/21/06, fredt
<[EMAIL PROTECTED]>
wrote:
If you just want the next value for a sequence, you can use a CALL
statement:
CALL NEXT VALUE FOR sequence_seq_id
----- Original Message -----
Sent: 21 April 2006 19:57
Subject: Re: [Hsqldb-developers] Re:
Issue with SEQUENCE
Thanks Fred:
I finally figured it out:
If I run:
SELECT NEXT VALUE FOR sequence_seq_id FROM test_sequence;
It returns as many values as there are records in the table starting
from the next available. This explains the 46 I got since I have 46 seqences
defined, the SYSTEM_SEQUENCES table had 46 entries.
NEXT VALUE FOR sequence_seq_id
placed by itself does not work - needs a FROM clause!
So I created a DUAL table with just one record and am running by next
value like so:
NEXT VALUE FOR sequence_seq_id FROM dual.
But I am concerned that the dual table might have additional records in
which case it will create a problem. Is there a way to lock it or to have a
SYSTEM table that always has 1 record that I can use the NEXT VALUE FOR
clause?
CREATE TABLE dual (
test INTEGER NOT NULL
);
INSERT INTO dual VALUES (1);
On 4/21/06, fredt
<[EMAIL PROTECTED] > wrote:
>> was similar to DUAL in
Oracle
The dual table is Oracle is just a table with a single
row. You can make your own.
>> the first field of
the table has the same name as the sequence
Same name or not, it is completely
irrelevant.
>> SELECT NEXT VALUE FOR sequence_seq_id FROM
test_sequence; does not return anything
Returns nothing because test_sequence has no
rows.
>> SELECT NEXT VALUE FOR sequence_seq_id FROM
test_sequence; This time it returns 1 (shouldn't it be 2).
It returns 1 because it is the first time a value from
the sequence has been returned. Next time you use the same SELECT, it will
return 2.
Fred
----- Original Message -----
Sent: 21 April 2006 19:21
Subject: Re: [Hsqldb-developers] Re:
Issue with SEQUENCE
I assumed that SYSTEM_SEQUENCES was similar to DUAL in Oracle in that
you can run NEXTVAL for a sequence name.
Based upon your suggestion, here is what I did:
1. Created SEQUENCE
CREATE SEQUENCE sequence_SEQ_ID
AS INTEGER
START WITH
1
INCREMENT BY 1;
2. Create TABLE
CREATE TABLE test_sequence
(
sequence_seq_id INTEGER NOT
NULL
,description VARCHAR(50) NOT
NULL
);
Notice that the first field of the table has the same name as the
sequence.
3. Next value?
SELECT NEXT VALUE FOR sequence_seq_id FROM test_sequence;
does not return anything
4. Insert a record into test_sequence table
INSERT INTO test_sequence VALUES (1,'test');
5. Try again
SELECT NEXT VALUE FOR sequence_seq_id FROM test_sequence;
This time it returns 1 (shouldn't it be 2).
Please help.
Nitin
On 4/21/06, fredt <[EMAIL PROTECTED] > wrote:
SYSTEM_SEQUENCES should not be used for getting
sequence values. Use your own tables. For example
SELECT NEXT VALUE FOR login_password_SEQ FROM my_table;
Sequences are designed mainly for inserting new rows,
or for updating existing rows, e.g.
INSERT INTO my_table (a, b, c) VALUES (NEXT VALUE FOR
login_password_seq, 10, 'a string');
Fred
----- Original Message -----
Sent: 21 April 2006 18:31
Subject: Issue with
SEQUENCE
I have recently started using SEQUENCES in HSQLDB (version
1.8.0.4)
CREATE SEQUENCE login_password_SEQ
AS INTEGER
START WITH
1
INCREMENT BY 1;
When I issue:
SELECT NEXT
VALUE FOR login_password_SEQ FROM
INFORMATION_SCHEMA.SYSTEM_SEQUENCES
It produces 46 values! The first time it creates 1 thru 46, the
second 47 thru 92......
This is true for any other SEQUENCE also.
What am I doing wrong?
--
Nitin
Uchil
--
Nitin Uchil
(734)945-6463
--
Nitin Uchil
(734)945-6463
--
Nitin Uchil
(734)945-6463
