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28.7.7.38 mysql_insert_id()

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uint64_t mysql_insert_id(MYSQL *mysql)

Description

Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field, or have used INSERT or UPDATE to set a column value with LAST_INSERT_ID(expr).

The return value of mysql_insert_id() is always zero unless explicitly updated under one of the following conditions:

INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit nonspecial value.
In the case of a multiple-row INSERT statement, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value that was successfully inserted.
If no rows are successfully inserted, mysql_insert_id() returns 0.
If an INSERT ... SELECT statement is executed, and no automatically generated value is successfully inserted, mysql_insert_id() returns the ID of the last inserted row.
If an INSERT ... SELECT statement uses LAST_INSERT_ID(expr), mysql_insert_id() returns expr.
INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column or by updating any column to LAST_INSERT_ID(expr).
If the previous statement returned an error, the value of mysql_insert_id() is undefined.

The return value of mysql_insert_id() can be simplified to the following sequence:

If there is an AUTO_INCREMENT column, and an automatically generated value was successfully inserted, return the first such value.
If LAST_INSERT_ID(expr) occurred in the statement, return expr, even if there was an AUTO_INCREMENT column in the affected table.
The return value varies depending on the statement used. When called after an INSERT statement:
- If there is an AUTO_INCREMENT column in the table, and there were some explicit values for this column that were successfully inserted into the table, return the last of the explicit values.
When called after an INSERT ... ON DUPLICATE KEY UPDATE statement:
- If there is an AUTO_INCREMENT column in the table and there were some explicit successfully inserted values or some updated values, return the last of the inserted or updated values.

mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.

The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.

The LAST_INSERT_ID() SQL function will contain the value of the first automatically generated value that was successfully inserted. LAST_INSERT_ID() is not reset between statements because the value of that function is maintained in the server. Another difference from mysql_insert_id() is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific nonspecial value. See Section 12.15, “Information Functions”.

mysql_insert_id() returns 0 following a CALL statement for a stored procedure that generates an AUTO_INCREMENT value because in this case mysql_insert_id() applies to CALL and not the statement within the procedure. Within the procedure, you can use LAST_INSERT_ID() at the SQL level to obtain the AUTO_INCREMENT value.

The reason for the differences between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide more exact information about what happens to the AUTO_INCREMENT column.

Note

The OK packet used in the client/server protocol holds information such as is used for session state tracking. When clients read the OK packet to know whether there is a session state change, this resets values such as the last insert ID and the number of affected rows. Such changes cause mysql_insert_id() to return 0 after execution of commands including but not necessarily limited to COM_PING, COM_REFRESH, and COM_INIT_DB.

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Return Values

Described in the preceding discussion.

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Errors

ER_AUTO_INCREMENT_CONFLICT
A user-specified AUTO_INCREMENT value in a multi INSERT statement falls within the range between the current AUTO_INCREMENT value and the sum of the current and number of rows affected values.

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