How Can I Use a Different Column as Primary Key While Maintaining Auto-Increment in MySQL?

Maintaining Auto-Increment and Using Another Column as Primary Key in MySQL

In MySQL, when creating a table with an auto-incrementing column, the default behavior is for that column to also be the primary key. However, this behavior can lead to performance issues if queries primarily identify rows using a different column.

Consider the following scenario: you create a table with a column named id as the auto-incrementing primary key and another column named memberid that is unique and used in queries to identify members. In this case, it would be ideal to use memberid as the primary key for performance reasons, but doing so would cause an error:

1075 - Incorrect table definition; there can be only one auto column and it must be defined as a key

To address this, the best solution is to retain the id column for maintaining the auto-incrementing functionality while defining memberid as the primary key. This can be achieved by creating an index (key) on the id column, as shown below:

CREATE TABLE members ( 
  id int(11)  UNSIGNED NOT NULL AUTO_INCREMENT,
  memberid VARCHAR( 30 ) NOT NULL , 
  `time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP , 
  firstname VARCHAR( 50 ) NULL , 
  lastname VARCHAR( 50 ) NULL , 
  PRIMARY KEY (memberid) ,
  KEY (id)                          --- or:    UNIQUE KEY (id)
) ENGINE = MYISAM; 

This approach allows you to keep the auto-incrementing column for performance purposes while still using memberid as the primary key for efficient querying.

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