Based on what I know, I would say the schema should be minimally:

id, int(11) auto_increment
nickname, varchar 100
message, text
timestamp, int(11)
dateStamp, time/date

Some would argue that you don't need 2 timestamp fields. However in my experience, I sometimes have the need to search base on an EPOCH time range (timestamp) or to use MySQLs date system to search between certain dates.

My logic for this database is:

• You can limit queries base on nickname
• You can limit queries base on time range
• You can perform certain matches based on text
• Use a combination of any/all three

I've included an ID field. This field exists based on common database practices and for future growth. I feel that you may need to code a sub or script to parse a raw log to insert it into the database properly. It may get tricky depending on how the IRC formats the time stamp in the logs.

Hope this helps