I'm trying to create a sequence in MySQL (I'm very new to SQL as a whole). I'm using the following code, but it causes an error:
CREATE SEQUENCE ORDID INCREMENT BY 1 START WITH 622;
ORDID refers to a field in a table I'm using. How do I create the sequence properly?
Edit:
Allegedly, MySQL doesn't use sequences. I'm now using the following code, but this is causing errors too. How do I fix them?
CREATE TABLE ORD (
ORDID NUMERIC(4) NOT NULL AUTO_INCREMENT START WITH 622,
//Rest of table code
Edit:
I think I found a fix. For phpMyAdmin (which I was using) you can use the following code.
ALTER TABLE ORD AUTO_INCREMENT = 622;
I have no idea why it prefers this, but if anyone else needs help with this then here you go. :)
By creating the increment table you should be aware not to delete inserted rows. reason for this is to avoid storing large dumb data in db with ID-s in it. Otherwise in case of mysql restart it would get max existing row and continue increment from that point as mention in documentation http://dev.mysql.com/doc/refman/5.0/en/innodb-auto-increment-handling.html
This is a solution suggested by the MySQl manual:
If expr is given as an argument to LAST_INSERT_ID(), the value of the argument is returned by the function and is remembered as the next value to be returned by LAST_INSERT_ID(). This can be used to simulate sequences:
Create a table to hold the sequence counter and initialize it:
mysql> CREATE TABLE sequence (id INT NOT NULL); mysql> INSERT INTO sequence VALUES (0);
Use the table to generate sequence numbers like this:
mysql> UPDATE sequence SET id=LAST_INSERT_ID(id+1); mysql> SELECT LAST_INSERT_ID();
The UPDATE statement increments the sequence counter and causes the next call to LAST_INSERT_ID() to return the updated value. The SELECT statement retrieves that value. The mysql_insert_id() C API function can also be used to get the value. See Section 23.8.7.37, “mysql_insert_id()”.
You can generate sequences without calling LAST_INSERT_ID(), but the utility of using the function this way is that the ID value is maintained in the server as the last automatically generated value. It is multi-user safe because multiple clients can issue the UPDATE statement and get their own sequence value with the SELECT statement (or mysql_insert_id()), without affecting or being affected by other clients that generate their own sequence values.
SEQUENCES like it works on firebird:
-- =======================================================
CREATE TABLE SEQUENCES
(
NM_SEQUENCE VARCHAR(32) NOT NULL UNIQUE,
VR_SEQUENCE BIGINT NOT NULL
);
-- =======================================================
-- Creates a sequence sSeqName and set its initial value.
-- =======================================================
DROP PROCEDURE IF EXISTS CreateSequence;
DELIMITER :)
CREATE PROCEDURE CreateSequence( sSeqName VARCHAR(32), iSeqValue BIGINT )
BEGIN
IF NOT EXISTS ( SELECT * FROM SEQUENCES WHERE (NM_SEQUENCE = sSeqName) ) THEN
INSERT INTO SEQUENCES (NM_SEQUENCE, VR_SEQUENCE)
VALUES (sSeqName , iSeqValue );
END IF;
END :)
DELIMITER ;
-- CALL CreateSequence( 'MySequence', 0 );
-- =======================================================================
-- Increments the sequence value of sSeqName by iIncrement and returns it.
-- If iIncrement is zero, returns the current value of sSeqName.
-- =======================================================================
DROP FUNCTION IF EXISTS GetSequenceVal;
DELIMITER :)
CREATE FUNCTION GetSequenceVal( sSeqName VARCHAR(32), iIncrement INTEGER )
RETURNS BIGINT -- iIncrement can be negative
BEGIN
DECLARE iSeqValue BIGINT;
SELECT VR_SEQUENCE FROM SEQUENCES
WHERE ( NM_SEQUENCE = sSeqName )
INTO @iSeqValue;
IF ( iIncrement <> 0 ) THEN
SET @iSeqValue = @iSeqValue + iIncrement;
UPDATE SEQUENCES SET VR_SEQUENCE = @iSeqValue
WHERE ( NM_SEQUENCE = sSeqName );
END IF;
RETURN @iSeqValue;
END :)
DELIMITER ;
-- SELECT GetSequenceVal('MySequence', 1); -- Adds 1 to MySequence value and returns it.
-- ===================================================================
If You need sth different than AUTO_INCREMENT you can still use triggers.
Source: Stackoverflow.com