>>Suppose you have a lookup table with one character field. Selections from this table are entered in a related field in some other table. If the strings in the lookup table were really long, most of us would make a keyfield for the lookup table and store that key in the related table, instead of the long string. But many would not bother if the strings were only a few characters. For the sake of speed, where do you draw the line? Six characters? Twenty? Also, does the number of records in the lookup table make a difference?
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>From normalized data standpoint you should have at least 2 fields in lookup table: ID (primary key) and Description.

Would you make an ID field even if the Description had unique values and was, say, three characters long? My question is: where do you draw the line?

Mark Mccasland says that frequency of lookup table modification affects this decision, but I'm not sure how.