Are unique indices on Access text fields always case insensitive?

问题

I created an MS Access table using the following code:

  tbl := Database.CreateTableDef('English', 0, '', '');
  try
    fld := tbl.CreateField('ID', dbLong, 0);
    fld.Attributes := dbAutoIncrField + dbFixedField;
    tbl.Fields.Append(fld);

    fld := tbl.CreateField('Content', dbText, 255);
    fld.Required := true;
    fld.AllowZeroLength := false;
    tbl.Fields.Append(fld);

    Database.TableDefs.Append(tbl);

    idx := tbl.CreateIndex('PrimaryKey');
    idx.Fields.Append(idx.CreateField('ID', EmptyParam, EmptyParam));
    idx.Primary := True;
    idx.Unique := true;
    tbl.Indexes.Append(idx);

    idx := tbl.CreateIndex('IX_Content');
    idx.Fields.Append(idx.CreateField('Content', EmptyParam, EmptyParam));
    idx.Primary := false;
    idx.Unique := true;
    tbl.Indexes.Append(idx);
  finally
    tbl := nil;
  end;

This works fine until I try to insert the two strings 'Field type' and 'Field Type' into this table. I get an error telling me that the unique index restricts me from doing that. As you can see they only differ in the case of the second word. Since I did not explicitly make the index case insensitive (I wouldn't even know how to do that), I don't quite understand why this happens. Are indices on text fields always case insensitive in MS Access? If not, what am I doing wrong?

回答1:

Access Jet databases are fundamentally case insensitive. That is your problem. As far as I know there is no way to make an Access index case sensitive.

回答2:

Use Binary field

Case insensivity problem in Microsoft Access was long time ago addressed in article KB244693 published by Microsoft and still can be found in Web archive.

Basically, the solution is to add a Binary field into your MS Access table and that one is finally case sensitive (uses Unicode for storing binary content) and still can be used as a text field with operators =, LIKE etc.

The field of type Binary cannot be added via the UI, but you add it to your existing table using SQL statement like this:

ALTER TABLE Table1
  ADD COLUMN BinaryField1 BINARY(50)

Then you can manage it normally via the Access UI.

来源：https://stackoverflow.com/questions/4305715/are-unique-indices-on-access-text-fields-always-case-insensitive

标签

Delphi

ms-access

indexing