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

Use appropriate data types

Data types store information about specific sets of data, including ranges of values, the operations that can be performed on those values, and how the values are stored in memory. You can improve performance by using the appropriate data type for your data. For instance, avoid assigning a data type of char or string to values that only contain numeric data. And whenever possible, choose economical data types over the more expensive numeric and string types.