Summary
Microsoft Visual FoxPro has a new index type, Primary. The Primary index, however, cannot be created in a program by using the INDEX command. This article shows by example how to add or modify a Primary index in a program.
More Information
A Primary index is an index that never permits duplicate values on the specified field or expression. The Primary index may be established in the database container interface or in a program by using the CREATE TABLE or ALTER TABLE command.
A table with a Primary index must be part of a database and cannot be a free table. The first example shows how to create a table with a Primary index. The second example shows how to alter an existing table to change a Primary key. The third example adds a Primary index to an existing table.
Example 1 - Create a New Table with a Primary Index
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Create a new database, or open an existing one.
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Issue the following command in the Command window to create a table with a Primary index on the cSsn key field:
CREATE TABLE employee (cSsn C(11) PRIMARY KEY, cLast C(20),;
cFirst C(20))
Example 2 - Modify an Existing Table to change a Primary Index
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Open the database used in example 1.
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Issue the following command from the Command window to move the Primary index from the cSsn field to the cLast field:
ALTER TABLE employee DROP PRIMARY KEY ADD PRIMARY KEY cLast TAG cLast
Example 3 - Modify an Existing Table to add a Primary Index
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Add a new table to an existing database with this command:
CREATE TABLE noprime (cLast C(20))
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From the Command window, add a Primary index to the existing table by using one of the following commands:
ALTER TABLE noprime ADD PRIMARY KEY cLast TAG cLast
-or-
ALTER TABLE noprime ALTER COLUMN cLast C(20) PRIMARY KEY
