If a table has a primary key defined on any field (s), then you cannot have two records having the same value of that field (s).Ī table can have only one PRIMARY KEY either on one column or multiple columns. When multiple fields are used as a primary key, they are called a composite key. A table can have only one primary key, which may consist of single or multiple fields. sqlitestudio composite primary keyĪ primary key column cannot have NULL values. To show how this works, first define two database tables that don’t have any foreign keys: Next, define a SQLite table that has two foreign keys, one that relates a new orders table back to the customers table, and a second foreign key that relates the orders table back to the salespeople table: As you can see, the SQLite foreign key syntax is very similar to other databases.
Therefore, the only way you can “add” a foreign key to an existing table in SQLite is to create a new table with a foreign key, then transfer the data to the new table.Ī SQLite foreign key example. In other words, you can’t use ALTER TABLE to add a foreign key to an existing table like you can in other database management systems. A foreign key can only be defined in a CREATE TABLE statement. The foreign key in the child table will generally reference a primary key in the parent table. The referenced table is called the parent table while the table with the foreign key is called the child table. A foreign key means that values in one table must also appear in another table. While working with multiple tables, when there are two tables that relate to each other with one column in common.Ī foreign key is a way to enforce referential integrity within your SQLite database. The SQLite foreign key is a constraint that verifies the existence of value present in one table to another table that has a relation with the first table where the foreign key is defined. This is because it has been defined using INTEGER PRIMARY KEY. Example: CREATE TABLE Cats( CatId INTEGER PRIMARY KEY, CatName ) In this table, the CatId column is an autoincrement column. You can create it explicitly with the AUTOINCREMENT keyword.īy default, when you define a column as INTEGER PRIMARY KEY, it will auto-increment whenever you insert NULL into that column. There are a couple of ways you can create an AUTOINCREMENT column: You can create it implicitly when you define the column as INTEGER PRIMARY KEY. In SQLite, an AUTOINCREMENT column is one that uses an automatically incremented value for each row that’s inserted into the table. If you don’t have any requirement like this, you should not use the AUTOINCREMENT attribute in the primary key.
The main purpose of using attribute AUTOINCREMENT is to prevent SQLite to reuse a value that has not been used or a value from the previously deleted row.
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