Surrogate Key Generates Non-numeric Values

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To generate keys in sequence from the highest value that was last used, set the Generate Key from Last Highest Value property to Yes. Any gaps in the key range are ignored. To specify a value to initialize the key source, add the File Initial Value property to the Options group, and specify the start value for key. Jan 21, 2016 Specify CYCLE to indicate that the sequence continues to generate values after reaching either its maximum or minimum value. After an ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches. Primary keys are used in OLTP whereas surrogate keys are used in OLAP schemas. Primary keys hold some business meaning whereas surrogate does not hold any business meaning. Primary key may contain numeric as well as non-numeric values whereas surrogate keys contain only (simple)numeric values. A many/many table with 2 surrogate parent keys will have a multiple column PK. However, it doesn't need another surrogate column. If a table does have a surrogate (IDENTITY etc) key then it doesn't need to be multiple column. You can have a super key that includes the surrogate but this would be to enforce other rules (eg subtypes).

The surrogate key is a unique, numeric value that is appended to the relation. Surrogate keys are used in situations when no suitable primary key exists within the user data, or when all available primary keys within the data are too cumbersome for an efficient design. Surrogate key values have no meaning to the users and are normally hidden on. 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. Aug 19, 2018 The Surrogate Key Generator stage is a processing stage that generates surrogate key columns and maintains the key source. A surrogate key is a unique primary key that is not derived from the data that it represents, therefore changes to the data will not change the primary key.

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.

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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() 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: