![]() ![]() In other words, if you insert NULL into that column, it will be converted to the current ROWID.Īctually, the way it works is that the column becomes an alias for the ROWID. When you do this, any NULL values are converted into the the current ROWID. Therefore, you don’t actually need to use the AUTOINCREMENT keyword to have a column that uses an automatically incrementing value for each row. When you declare a column as INTEGER PRIMARY KEY, it will automatically increment. However, there are some subtle differences between how each method works. One downside of this method is that it uses extra CPU, memory, disk space, and disk I/O overhead.īoth methods cause the column to use an incrementing value each time a new row is inserted with NULL in that column. You can create it explicitly with the AUTOINCREMENT keyword.You can create it implicitly when you define the column as INTEGER PRIMARY KEY.There are a couple of ways you can create an AUTOINCREMENT column: Now, let's demonstrate how the cascade delete works.In SQLite, an AUTOINCREMENT column is one that uses an automatically incremented value for each row that’s inserted into the table. In this example, we've created a foreign key (with cascade delete) called fk_departments that references the departments table based on the department_id field. INSERT INTO employees SELECT * FROM _employees_old Now, let's add a foreign key with cascade delete to the employees table: PRAGMA foreign_keys=off ĪLTER TABLE employees RENAME TO _employees_old INSERT INTO employees VALUES (10001, 'Anderson', 'Dave', 999) ![]() INSERT INTO employees VALUES (10000, 'Smith', 'John', 30) INSERT INTO departments VALUES (999, 'Sales') ![]() INSERT INTO departments VALUES (30, 'HR') Next, let's add some data to these tables: INSERT INTO table1 SELECT * FROM _table1_old įirst, let's start by creating our 2 tables ( departments and employees): The syntax to add a foreign key with cascade delete to an existing table in SQLite is: PRAGMA foreign_keys=off ĪLTER TABLE table1 RENAME TO _table1_old Instead you will need to rename the table, create a new table with the foreign key, and then copy the data into the new table. You can not use the ALTER TABLE statement to add a foreign key with cascade delete in SQLite. How to Add a Foreign Key with Cascade Delete to an Existing Table Then we've created a foreign key called fk_departments on the employees table that references the departments table based on the department_id field.īecause of the cascade delete, when a record in the departments table is deleted, all records in the employees table will also be deleted that have the same department_id value. In this example, we've created a primary key on the departments table that consists of only one field - the department_id field. ( employee_id INTEGER PRIMARY KEY AUTOINCREMENT, ( department_id INTEGER PRIMARY KEY AUTOINCREMENT, Let's look at an example of how to create a foreign key with cascade delete using the CREATE TABLE statement in SQLite. REFERENCES parent_table (column1, column2. The syntax for creating a foreign key with cascade delete using a CREATE TABLE statement in SQLite is: CREATE TABLE table_nameįOREIGN KEY (column1, column2. How to Create a Foreign Key with Cascade Delete using a CREATE TABLE statement Syntax ![]()
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