How to change the primary key for already existing table?
You can do this with an "ALTER TABLE" command:
Suppose you had the following sample table with id as the primary key:
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create table mytest (
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id int not null default 0,
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some_val in not null default 0,
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foo varchar(32),
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primary key (id));
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Given the above table, the sample "ALTER TABLE" commands would be:
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alter table mytest
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drop primary key;
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alter table mytest
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add primary key(id,some_val);
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Keep in mind, however, that the data in your existing table may affect your ability to effectively change the primary key, such as any NULL values in a field. Any fields you want to add to the primary key definition must be declared as "NOT NULL", so you may have to alter that column as well.
Rick
