FastTips: Tables Questions & Answers

PSS ID Number:  Q100844
Article last modified on 08-27-1993

1.00 1.10
WINDOWS

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  Microsoft® Product Support Services Application Note (Text File)
            WX0635: DATABASE STRUCTURE QUESTIONS & ANSWERS
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                                              Revision Date: 5/93
                                                 2 Pages, No Disk
The following information applies to Microsoft Access, version 1.0.
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    Q. What foreign data formats does Microsoft Access support?
    A. Microsoft Access can link to Btrieve®, dBASE III PLUS®,
       dBASE IV®, and Paradox® versions 3.x data, including
       indexes.
       Microsoft Access can import data from Btrieve, dBASE III PLUS,
       dBASE IV, FoxPro® versions 2.x, Lotus® 1-2-3® versions
       2.x and 3.x, Lotus 1-2-3/W, Microsoft Excel versions 2.x and
       later for Windows, Paradox 3.x, and fixed-length and delimited
       ASCII text.
       Microsoft Access also supports the Open Database Connectivity
       (ODBC) specification for connectivity to data on database
       servers. ODBC drivers for Microsoft SQL Server are included
       with Microsoft Access. Microsoft SQL Server ODBC drivers are
       the only drivers certified for Microsoft Access version 1.0.
2.  Q. What are primary and foreign keys in a relational database?
    A. Primary keys uniquely identify a specific row in a table. They
       are usually composed of a single field or column whose data is
       unique to each row of information (for example, a customer
       identification number, employee social security number, or
       order identification number). Primary keys also can be composed
       of more than one field. For example, the fields Company
       Identification and Contact Name could be combined to form a
       primary key for a table that contains information about
       companies that have more than one contact.
       Foreign keys identify rows in one table that match the primary
       key of another table. For example, if the field Employee ID is
       the primary key in the Employee table, in the Orders table,
       Employee ID is the foreign key. The relationship between
       primary and foreign keys enables you to access related data in
       multiple tables.
3.  Q. Which FieldSize setting should I select for the Number data
       type in order to use a Counter field of another table as the
       foreign key in the current table?
    A. To use a Counter field of another table as the foreign key in
       the current table, select the Long Integer setting.
 4. Q. How do you change the starting value of a Counter column to a
       number other than 1?
    A. To set the starting value of a Counter column to a number other
       than 1, use the following four-step procedure:
       1. Create an additional single-column temporary table. Give the
          Number column the same name as the Counter column in the
          original table.
       2. Create a new row in the temporary table by inserting a value
          in the Number column. This value should be 1 less than the
          desired starting value for the original table.
       3. Create an Append query to append the single row from the
          temporary table to the original table.
       4. Once you append the single row, delete the temporary table.
          You can then delete the dummy row from the original table.
        NOTE: Do not compact the database before you add the first row
        to the original table. If you do this, the counter value is
        reset to start at 1.
5.  Q. Is data in tables stored in a sorted order? How can I view my
       data in sorted order?
    A. Data in tables is not stored in sorted order. Data is stored in
       the order in which it was entered. To view data in sorted
       order, create a query, or a form based on a query, that uses
       the Sort field on the query grid. By default, if the table
       includes a primary key, the Datasheet view of the table will
       display the data sorted by the primary key. To view the data
       sorted by something other than the primary key alone, use a
       query, as previously described.
6.  Q. How can I delete the primary key from a table?
    A. You can delete the primary key for a table by opening the Table
       Properties dialog box and deleting the entry for the Primary
       Key field. Please note that the primary key cannot be deleted
       from a table that is the primary table in a relationship.
7.  Q. How can I create computed columns in tables?
    A. You can create computed columns or expressions with queries.
       Within the query, create a column that is defined as an
       expression. In general, it is helpful to think of queries as
       virtual tables; you can use a query wherever you can use a
       table. If you're familiar with SQL terminology, this is very
       similar to creating a view. Unlike most implementations of
       views, however, Microsoft Access views can be updated even if
       they involve joins from different data sources, such as
       Paradox, Btrieve, or separate Microsoft Access data sources.
8.  Q. Two of my tables have Counter data type columns in common. Why
       can't I define a relationship between the two tables based on
       these columns?
    A. You can define only one-to-one relationships between Counter
       data type columns. If the linking column on the "one" side is a
       counter, define the linking column on the "many" side as a long
       integer.
       For more information on table relationships, see the "Microsoft
       Access User's Guide", Chapter 1, "Designing a Database," pages
       13-18.

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