- #Unable to delete records in db browser for sqlite how to
- #Unable to delete records in db browser for sqlite free
This operation defragments the database objects, ignores the free spaces, and repacks individual pages. SQLite first copies data within a database file to a temporary database. SQLite provides the VACUUM command to address all three issues above. Therefore, it increases the number of pages to hold a table. Because of this, it increases storage overhead for the table, takes more time to read/write, and decreases the cache performance. It decreases the number of rows that can be stored in a single page. Third, the insert, update and delete operations create unused data block within individual database pages. Second, when you insert or delete data from the tables, the indexes and tables become fragmented, especially for the database that has a high number of inserts, updates, and deletes. As a result, the size of the database file always grows in size. Why do you need SQLite VACUUM commandįirst, when you drop database objects such as tables, views, indexes, and triggers or delete data from tables, the database file size remains unchanged. Because SQLite just marks the deleted objects as free and reserves it for the future uses.
#Unable to delete records in db browser for sqlite how to
Now, let's demonstrate how the cascade delete works.Summary: in this tutorial, we will explain why you need to use the SQLite VACUUM command and show how to use it to optimize the database file. 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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