Surrogate Key Generates Non-numeric Values

Posted on 10.12.202022.08.2017by admin

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Summary: in this tutorial, you will learn how to use the MySQL LAST_INSERT_ID() function to returns the first automatically generated integer successfully inserted for an AUTO_INCREMENT column.

A surrogate key is an artificial or synthetic key that is used as a substitute for a natural key. Actually, a surrogate key in a data warehouse is more than just a substitute for a natural key. In a data warehouse, a surrogate key is a necessary generalization of the natural production key and is one of the basic elements of data warehouse design. If what you choose is not a nature key, but a system generated identifier, it is called surrogate key. Or we can say that you use a surrogate key' as the primary key. In the avove example, the customerid is a surrogate key and the customernumber is the nature key. These are just terms to describe the table design. The values of generated surrogate keys have no relationship to the real-world meaning of the data held in a row. When inspecting a row holding a foreign key reference to another table using a surrogate key, the meaning of the surrogate key's row cannot be discerned from the key itself. Every foreign key must be joined to see the related data item. In general, surrogate keys (such as arbitrary numeric identifiers) undermine the integrity of the database. Primary keys are the main way of identifying rows in the database; if the primary key values are not meaningful, the constraint is not meaningful. Any foreign keys that refer to surrogate primary keys are therefore also suspect. Re: st: finding non-numeric characters before I can destring. From: 'Ben Jann' Prev by Date: Re: st: finding non-numeric characters before I can destring; Next by Date: RE: st: How to merge those files; Previous by thread: Re: st: finding non-numeric characters before I can destring.

Introduction to MySQL `LAST_INSERT_ID()` function

In database design, we often use a surrogate key to generate unique integer values for the primary key column of a table by using the AUTO_INCREMENT attribute:

When you insert a row into the table without specifying a value for the id column, MySQL automatically generates a sequential unique integer for the id column.

The LAST_INSERT_ID() function returns the first automatically generated integer ( BIGINT UNSIGNED) successfully inserted for an AUTO_INCREMENT column.

If you insert multiple rows into the table using a single INSERT statement, the LAST_INSERT_ID() function returns the first automatically generated value only.

If the insertion fails, the result returned by the LAST_INSERT_ID() remain unchanged.

The LAST_INSERT_ID() function works based on client-independent principle. It means the value returned by the LAST_INSERT_ID() function for a specific client is the value generated by that client only to ensure that each client can obtain its own unique ID.

MySQL `LAST_INSERT_ID` function examples

Let’s look at an example of using MySQL LAST_INSERT_ID function.

A) Using MySQL `LAST_INSERT_ID()` function to get value when inserting one row into a table

First, create a new table named messages for testing. In the messages table, we set the AUTO_INCREMENT attribute for the id column.

Second, insert a new row into the messages table.

Third, use the MySQL LAST_INSERT_ID function to get the inserted value of the id column:

Fourth, attempt to insert a null value into the description column:

MySQL issued the following error:

Finally, use the LAST_INSERT_ID function to get the last automatically inserted value:

The result is unchanged.

B) Using MySQL `LAST_INSERT_ID()` function to get value when inserting multiple rows into a table

First, insert three rows into the messages table:

Second, query data form the messages table:

Third, use the LAST_INSERT_ID() function to get the inserted value:

As you can see clearly from the output, the LAST_INSERT_ID()/call-of-duty-black-ops-2-key-generator-password.html. function returns the generated value of the first row successfully inserted, not the last row.

C) Using MySQL `LAST_INSERT_ID()` function in a stored procedure

First, create two tables accounts and phones for testing:

Second, create a stored procedure that inserts an account with a phone number into both tables:

The stored procedure inserts a row into the accounts table, get the account id using the LAST_INSERT_ID() function, and use this account id for inserting a phone into the phones table. A row in the phones table should only exist if there is a corresponding row in the accounts table, therefore, we put both inserts into a transaction.

Third, call the stored procedure CreateAccount to create a new account with a phone number:

Fourth, query data from the accounts table:

And phones table:

It works as expected.

Finally, attempt to create a new account with the value of the last name is null:

MySQL issued an error:

In this tutorial, you have learned how to use the MySQL LAST_INSERT_ID function to return the first automatically generated integer successfully inserted for an AUTO_INCREMENT column.