用键插入Android数据库

Question

So I want to have an integer ID primary field which autoincrements. Then I also want another key with a text field. Two entries cannot have the same ID nor can they have the same text field. The problem is that if the ID's are different but the text fields the same, I still don't want them to be inserted. Unfortunately creating a table with two primary keys means that it CAN be inserted. Is there anyway to express this besides two primary keys?

Answer 1

A table can have only one primary key. When you write

CREATE TABLE T1 ... PRIMARY KEY (A, B)

you're not actually creating two primary keys, but rather a single composite (ie multi-column) primary key. In this case, it means that two rows cannot share the same values of both A and B .

If you need both A and B to be unique by themselves, then you need to use a UNIQUE constraint (or, alternatively, a unique index).

From the SQLite documentation :

A UNIQUE constraint is similar to a PRIMARY KEY constraint, except that a single table may have any number of UNIQUE constraints. For each UNIQUE constraint on the table, each row must contain a unique combination of values in the columns identified by the UNIQUE constraint.

For example:

CREATE TABLE T1 (A INTEGER PRIMARY KEY, B INTEGER UNIQUE ...)