Question

What is the best way to generate a manually int primary key with mysql?

I dont want to use the autoincrement feature.

I taught to create a table with one column of type int named sequence. So every time I’m going to insert a new record first check this column and use the value as the primary key. Then after the insert is successful increment the value of sequence.

Is this a good aproach?

Answer 1

Create a table with one int column of type InnoDB:

CREATE TABLE key_table ( next_value INT NOT NULL DEFAULT 0 ) ENGINE=InnoDB;

Then when you want to get a new value for the key you must start a transaction (using the API you are using) and then:

SELECT next_value FROM key_table FOR UPDATE

Then read the value returned, it is the value for your primary key. Then to increment the value while still in the same transaction execute:

UPDATE key_table SET next_value = next_value + 1;

Then commit your transaction.

This will ensure complete consistency if and only if you use transaction as described above and you use the InnoDB table type.