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Excerpts from this Manual mysql_insert_id()

my_ulonglong mysql_insert_id(MYSQL *mysql)


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:

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

  1. If there is an AUTO_INCREMENT column, and an automatically generated value was successfully inserted, return the first such value.

  2. If LAST_INSERT_ID(expr) occurred in the statement, return expr, even if there was an AUTO_INCREMENT column in the affected table.

  3. 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.

Return Values

Described in the preceding discussion.



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