Checking to see if an identical value for a primary key field already exists

Is there a better way to check and see if a certain value has already been inserted into a primary key field besides just doing a select * from .. where .. and seeing if it returns any rows before inserting the new record?

[This message has been edited by RyanP (edited June 29, 2000).]

The only better way is to not have to check the primary key. If you use NOT NULL AUTO_INCREMENT then the primary key is automatically incremented every time you do an INSERT.
i.e.
CREATE TABLE sometable ( sid INTEGER NOT NULL AUTO_INCREMENT,
text1 VARCHAR(255),
text2 VARCHAR(255),
number1 INTEGER,
date1 DATE,
PRIMARY KEY (sid)
);
Then the key is automatically incremented when inserted into. i.e.

$query = "INSERT INTO sometable VALUES (NULL, '$text1val', '$text2val', $num1, now() )";

After executing the query the key is inserted automatically when it detects the NULL.

Then if you need to know the primary key value. In PHP you would use:
$primaryKey = mysql_insert_id($mysql_result);
Other than that I don't know of a better way.