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Microsoft
Access Resource Center
Beware of SQL Code that Creates Tables without Unicode Compression
Provided by: FMS Development Team
Note: This information applies only to a Microsoft Access database (.mdb).
What is Unicode Compression?
Starting with Microsoft Access 2000 and continuing through the current version, all data for the Text data types (Text, Memo, or Hyperlink field) are stored in the Unicode 2-byte character format. Languages such as Chinese, Japanese, and Korean use the full 2-byte characters, but languages that use Latin characters (e.g. English, Spanish, and German) always use a 0 as the first byte. When a field's Unicode Compression property is set to Yes, any character whose first byte is 0 is compressed when it is stored and uncompressed when it is retrieved, thus saving space in the database.
By Default
By default, Unicode Compression is set to ‘Yes’ when you create the field via the table properties. It is when you create the field via SQL that you must explicitly state the Unicode Compression to be ‘Yes’. Otherwise, the setting is left untouched with a value of ‘No’. To see the property to ‘Yes’, use the WITH COMPRESSION (or WITH COMP) keywords at the field-level declaration.
IMPORTANT NOTES:
- The WITH COMPRESSION can be executed only through the Jet OLE DB provider and ADO.
- Creating the table via SQL (by DAO or ADO), the Unicode Compression is set to ‘No’ by default.
Setting the property
The Unicode Compression is a property setting of the field. After making the data type selection, the property is located on the General tab at the bottom of the table property page.
Is there a fast way to ensure I have the Unicode Compression turned on?
FMS's Total Access Analyzer performs detailed analysis of your Access database objects. The detection of the Unicode Compression property is just one of hundreds of checks that can be performed on your Microsoft Access application.
Example
The following example illustrates two fields, with and without Unicode Compression being set.
Public Sub CompressionPropertyTest()
Dim sql As String
sql = "Create Table MyFirstTable ( FirstName_CompressionOFF Text(15), " & _
"LastName_CompressionON Text(15) WITH COMPRESSION)"
CurrentProject.Connection.Execute sql
End Sub
