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• Is the field a Date or a Time?
• To store a unique day use type Date.
• To store a unique moment in time use type DateTime (in preference to two separate Date and Time fields).
• To store a non-unique time, which is unusual, use Time.
• Is it a True/False value? If so, use Boolean.
• Is it a number? If there are no decimal places use type Integer otherwise use type Packed.
• Then it must be a string of characters or some other stream of bytes.
• Is it normally kept in a specialized type of file or document (eg: an image, a sound, an MS-Word document or an XML document)? Use type BLOB.
• Do you expect it to be subjected to normal code page conversions? If not, use VarBinary unless your data is always the same length, in which case you may choose to use Binary.
• Will the field be 256 bytes or less and be best stored as a fixed length field? If yes, and it only needs to support one language at execution time, use type Alpha.
• Will it ever be longer than 65535 bytes? Use type CLOB.
• Do you store the field as a variable length with any trailing blanks significant (for example, included in field concatenation operations)? If it only needs to support one language at execution time, use type String. Otherwise, use type NVarChar.
• Otherwise, it is fixed length. If it only needs to support one language at execution time, use type Char. Otherwise, use type NChar.

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