Set Default Integer Values in SQLite

Purpose:

• To ensure data consistency and avoid null values in the column.
• To automatically assign a specific integer value to new rows inserted into a table without explicitly specifying it in the INSERT statement.

Syntax:

CREATE TABLE table_name (
    column_name INTEGER DEFAULT default_value
);

• DEFAULT default_value: Specifies that the column should have a default value of default_value, which must be an integer.
• column_name: The name of the integer column.
• table_name: The name of the table you're creating.

Example:

CREATE TABLE users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT,
    age INTEGER DEFAULT 18
);

• When you insert a new row without specifying the age, it will automatically be set to 18.
• This creates a users table with an age column that has a default value of 18.

Additional Notes:

• You can modify the default value of an existing column using an ALTER TABLE statement:

ALTER TABLE table_name ALTER COLUMN column_name DEFAULT new_default_value;

• If you want to remove the default value, set it to NULL:

ALTER TABLE table_name ALTER COLUMN column_name DEFAULT NULL;

• The default value is applied when a new row is inserted. It does not affect existing rows.

Benefits:

• Clarity: Makes the table's structure more explicit.
• Efficiency: Saves time when inserting many rows.
• Data consistency: Ensures that all rows have a valid value for the column.

Setting Default Integer Values in SQLite

Creating a Table with a Default Integer Value

CREATE TABLE users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT,
    age INTEGER DEFAULT 18
);

• Explanation: This creates a users table with an age column. The DEFAULT 18 clause specifies that the default value for the age column is 18. If you insert a new row without explicitly providing an age value, it will automatically be set to 18.

Inserting Rows with the Default Value

INSERT INTO users (name) VALUES ('Alice');

• Explanation: This inserts a new row into the users table. Since no age value is provided, the default value of 18 will be used. The resulting row will have id (auto-incremented), name set to 'Alice', and age set to 18.

Modifying the Default Value

ALTER TABLE users ALTER COLUMN age DEFAULT 20;

• Explanation: This changes the default value for the age column to 20. Any new rows inserted after this modification will have an age of 20 unless a different value is specified.

ALTER TABLE users ALTER COLUMN age DEFAULT NULL;

• Explanation: This removes the default value for the age column. From now on, new rows must explicitly specify an age value or the column will be NULL.

• You can use expressions in the DEFAULT clause. For example, DEFAULT (SELECT MAX(age) FROM users) would set the default age to the maximum existing age in the table.
• You can also set a default value for other data types, such as TEXT, REAL, and BLOB.

Alternative Methods for Setting Default Integer Values in SQLite

While the DEFAULT clause is the most common method, here are some alternative approaches:

Using a Trigger:

• Example:

  CREATE TRIGGER set_default_age
  BEFORE INSERT ON users
  BEGIN
      IF NEW.age IS NULL THEN
          NEW.age := 18;
      END IF;
  END;
  

  This trigger sets the age to 18 if it's not provided during insertion.
• Purpose: To set a default value based on complex logic or calculations.

Using a View:

• Example:

  CREATE VIEW users_with_defaults AS
  SELECT id, name, COALESCE(age, 18) AS age
  FROM users;
  

  This view returns the age as 18 if it's NULL.
• Purpose: To present a virtual table with computed default values.

Using Application Logic:

• Example:

  import sqlite3
  
  conn = sqlite3.connect('mydatabase.db')
  cursor = conn.cursor()
  
  # Insert a new row with a default age
  cursor.execute("INSERT INTO users (name) VALUES ('John')")
  conn.commit()
  

  In the application, you can check for NULL values and set the default before inserting.
• Purpose: To handle default values at the application level.

Choosing the Right Method:

The best method depends on your specific requirements:

• Application Control: If you want to handle defaults at the application level, use application logic.
• Complexity: If you need more complex logic, triggers or views might be necessary.
• Simplicity: The DEFAULT clause is generally the simplest and most efficient option.