I have a table with 3 fields: Id(PK,AI), Name(varchar(36)), LName(varchar(36)).
I have to insert name and last name, Id inserts automatically because of it's constraints,
Is There a way to Jump id auto increment value when it reaches 6?
for instance do this 7 times:
Insert Into table(Name, LName) Values ('name1', 'lname1') "And jump id to 7 if it is going to be 6"
It may sound stupid to do this but I have the doubt.
Also Jump and do not record id 6.
record only, 1-5, 7,8,9 and so on
What I want to achieve starts from a Union:
Select * From TableNames
Select * From TableNames_general
In the TableNames_general I assign it's first value so that when the user sees the table for the first time it will be displayed the record I inserted.
The problem comes when the user inserts a new record, if the Id of the inserted record is the same as the one I have inserted it will be duplicated, that is why I want to achieve when the users inserts one record and if the last insert id already exists just jump that record. this is because I must have different ids due to its relationship among child tables.
Identity column generate values for you, And its best left this way, You have the ability to insert specific values in Identity column but its best left alone and let it generate values for you.
Imagine you have inserted a value explicitly in an identity column and then later on Identity column generates the same value for you, you will end up with duplicates.
If you want to have your input in that column then why bother with identity column anyway ??
Well this is not the best practice but you can jump to a specific number by doing as follows:
MS SQL SERVER 2005 and Later
-- Create test table CREATE TABLE ID_TEST(ID INT IDENTITY(1,1), VALUE INT) GO -- Insert values INSERT INTO ID_TEST (VALUE) VALUES (1),(2),(3) GO -- Set idnentity insert on to insert values explicitly in identity column SET IDENTITY_INSERT ID_TEST ON; INSERT INTO ID_TEST (ID, VALUE) VALUES (6, 6),(8,8),(9,9) GO -- Set identity insert off SET IDENTITY_INSERT ID_TEST OFF; GO -- 1st reseed the value of identity column to any smallest value in your table -- below I reseeded it to 0 DBCC CHECKIDENT ('ID_TEST', RESEED, 0); -- execute the same commad without any seed value it will reset it to the -- next highest idnetity value DBCC CHECKIDENT ('ID_TEST', RESEED); GO -- final insert INSERT INTO ID_TEST (VALUE) VALUES (10) GO -- now select data from table and see the gap SELECT * FROM ID_TEST
If you query the database to get the last inserted ID, then you can check if you need to increment it, by using a parameter in the query to set the correct ID.
If you use MSSQL, you can do the following:
Before you insert check for the current ID, if it's 5, then do the following:
Also you might get away with the following scenario:
DBCC CHECKIDENT (Table, reseed, 6), it will reseed the table and in this case your next identity will be 7
If you're checking for current identity just after INSERT, you can use
SELECT @@IDENTITY or
SELECT SCOPE_IDENTITY() for better results (as rcdmk pointed out in comments)
Otherwise you can just use
SELECT MAX(Id) FROM Table
There's no direct way to influence the AUTO_INCREMENT to "skip" a particular value, or values on a particular condition.
I think you'd have to handle this in an An
AFTER INSERT trigger.
AFTER INSERT trigger can't update the values of the row that was just inserted, and I don't think it can make any modifications to the table affected by the statement that fired the trigger.
BEFORE INSERT trigger won't work either, because the value assigned to an
AUTO_INCREMENT column is not available in a
BEFORE INSERT trigger.
I don't believe there's a way to get SQL Server
IDENTITY to "skip" a particular value either.
If you need "unique" id values between two tables, there's a rather ugly workaround with MySQL: roll your own auto_increment behavior using triggers and a separate table. Rather than defining your tables with AUTO_INCREMENT attribute, use a
BEFORE INSERT trigger to obtain a value.
id value is supplied, and it's larger than the current maximum value from the auto_increment column in the dummy auto_increment_seq table, we'd need to either update that row, or insert a new one.
As a rough outline:
CREATE TABLE auto_increment_seq (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE=MyISAM; DELIMITER $$ CREATE TRIGGER TableNames_bi BEFORE INSERT ON TableNames FOR EACH ROW BEGIN DECLARE li_new_id INT UNSIGNED; IF ( NEW.id = 0 OR NEW.id IS NULL ) THEN INSERT INTO auto_increment_seq (id) VALUES (NULL); SELECT LAST_INSERT_ID() INTO li_new_id; SET NEW.id = li_new_id; ELSE SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq; IF ( NEW.id > li_max_seq ) THEN INSERT INTO auto_increment_seq (id) VALUES (NEW.id); END IF; END IF; END$$ CREATE TRIGGER TableNames_ai AFTER INSERT ON TableNames FOR EACH ROW BEGIN DECLARE li_max_seq INT UNSIGNED; SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq; IF ( NEW.id > li_max_seq ) THEN INSERT INTO auto_increment_seq (id) VALUES (NEW.id); END IF; END; DELIMITER ;
The id column in the table could be defined something like this:
TableNames ( id INT UNSIGNED NOT NULL DEFAULT 0 PRIMARY KEY COMMENT 'populated from auto_increment_seq.id' , ...
You could create an identical trigger for the other table as well, so the two tables are effectively sharing the same auto_increment sequence. (With less efficiency and concurrency than an Oracle
SEQUENCE object would provide.)
This doesn't really insure that the
id values between the tables are actually kept unique. That would really require a query of the other table to see if the id value exists or not; and if running with InnoDB engine, in the context of some transaction isolation levels, we might be querying a stale (as in, consistent from the point in time at the start of the transaction) version of the other table.
And absent some additional (concurrency killing) locking, the approach outline above is subject to a small window of opportunity for a "race" condition with concurrent inserts... the SELECT MAX() from the dummy seq table, followed by the INSERT, allows a small window for another transaction to also run a SELECT MAX(), and return the same value. The best we can hope for (I think) is for an error to be thrown due to a duplicate key exception.
This approach requires the dummy "seq" table to use the MyISAM engine, so we can get an Oracle-like AUTONOMOUS TRANSACTION behavior; if inserts to the real tables are performed in the context of a REPEATABLE READ or SERIALIZABLE transaction isolation level, reads of the MAX(id) from the seq table would be consistent from the snapshot at the beginning of the transaction, we wouldn't get the newly inserted (or updated) values.
We'd also really need to consider the edge case of an UPDATE of row changing the id value; to handle that case, we'd need BEFORE/AFTER UPDATE triggers as well.