ASA SQL User's Guide
  Monitoring and Improving Performance
    Top performance tips

Pay attention to the order of columns

Columns in a row are accessed in a sequential manner in the order of their creation. For example, in order to access columns at the end of a row, Adaptive Server Anywhere has to skip over any columns that appear earlier in the row. Primary key columns are always stored at the beginning of rows. For this reason, it is important to create tables such that small and/or frequently accessed columns are placed before seldom accessed columns in the table.