SQLite supports the different actions as follows.Īs per our requirement we can use any action. Mainly there are two constraints as follows. SQLite foreign key constraint or we can say action as follows.When we try to insert the above records at that time it shows an error message because common_id 4 does not exist in the dist_unit table.Now try to insert another record as follows.Ĭode: Insert into distributor (dist_name, common_id) values ("LG", 4) We successfully created a booth table as shown in the below screenshot as follows.Here common_id id foreign key reference from dist_units.In the above example we use a create table statement to create a new table name as distributor with attributes such as dist_id with integer data type and also have a primary key constraint, dist_name with text data type and common_id with integer data type as shown in above statement.Now create a distributor table with different attributes by using the following statement.Ĭode: create table distributor (dist_id integer primary key, dist_name text not null, common_id integer not null, foreign key (common_id) references dist_units (common_id)) Now first create two tables to implement foreign keys as follows.įirst create a dist_unit with different attributes by using the following statement as follows.Ĭode: create table dist_unit (common_id integer primary key, unit_name text not null) In the event that any current key is refreshed from the parent table, the exchange comes up short toward the finish of the inquiry. On update: This is default parameter in foreign key.If any existing related key is deleted at that time all ongoing executions end. On delete: This is the default parameter in foreign keys.When we use foreign key in table at that time we can control the operation by using different parameter as follows. If we need to disable foreign key at that time we can use the following command as follows. So when we need to enable foreign key at that time we can use the following command as follows. So if your table already has existing triggers, views, or foreign key constraints, it’s probably safer to use the recommended method.Basically foreign key constraints compile with SQLite library, so that purpose SQLite uses PRAGMA foreign_keys command to enable or disable the foreign key constraint at the run time. With my example, this method works just as well.īut this method also has the potential to corrupt references to the table in any existing triggers, views, and foreign key constraints. For example you could do it like this: PRAGMA foreign_keys = OFF Īnd it’s true. When looking at the previous example, you might be thinking that there’s a more efficient way to do it. I’ve put it there solely to change the way my terminal outputs the result (so that you don’t have to scroll sideways to view the result). mode line) has got nothing to do with creating a foreign key. Note that the first line of my command (. This time we can see the details of the foreign key constraint. Now let’s check the table for foreign key constraints again.mode line If you need to reconstruct any indexes, triggers, or views, do that after the ALTER TABLE statement that renames the table (just prior to COMMIT). PRAGMA foreign_keys = OFF įOREIGN KEY(TypeId) REFERENCES Types(TypeId) The following code adds a foreign key to our table by creating a new table with a foreign key constraint, transferring the data to that table, dropping the original table, then renaming the new table to the name of the original table. (That’s blank because there are no foreign key constraints on this table.) We can verify that there are no foreign keys by running the following command: PRAGMA foreign_key_list(Pets) Notice that I didn’t create a foreign key. Two tables, because one ( Types) will have the primary key and the other ( Pets) will have the foreign key. CREATE TABLE Types(Īctually, here I created two tables and populated them with data. Original Table Without Foreign Keyįirst, let’s create a table without a foreign key and populate it with data. To make it somewhat realistic, we’ll make sure the table already contains data. The SQLite documentation recommends a 12 step process for making schema changes to a table.įor the purposes of this article, we’ll just deal with adding a foreign key. There’s more than one way to do this, but there is a recommended way. 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. 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. The only things you can do with ALTER TABLE in SQLite is rename a table, rename a column within a table, or add a new column to an existing table. SQLite supports a very limited subset of the ALTER TABLE statement.
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