Automatic Timestamps in SQLite3: Using Default Values for Datetime Columns

SQLite doesn't have a specific "datetime" data type, but it can handle dates and times using the TEXT data type and interpreting the data as a formatted string. Here's how to create a table with a datetime column that automatically gets the current date and time whenever you insert a new row:

CREATE TABLE my_table (
  id INTEGER PRIMARY KEY,  -- Define other columns as needed
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

In this example:

• created_at is the column name for storing the datetime.
• DATETIME specifies the data type for the column.
• DEFAULT CURRENT_TIMESTAMP is the key part. It sets the default value for the column to the current date and time whenever a new row is inserted. CURRENT_TIMESTAMP is a special keyword in SQLite that automatically retrieves the current date and time.

1. Inserting data: When you insert data into the table, you can omit the created_at column in the INSERT statement. SQLite will automatically use the current date and time for that column since you've defined a default value.

Here's an example of inserting data:

INSERT INTO my_table (name, description)
VALUES ('My record', 'This is some text data');

In this case, the created_at column will be populated with the current date and time when the data is inserted.

Example 1: Basic Default Current Timestamp

CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  customer_name TEXT NOT NULL,
  order_date DATETIME DEFAULT CURRENT_TIMESTAMP
);

This code creates a table named "orders" with three columns:

• id: An integer that acts as the primary key (unique identifier) for each order.
• customer_name: A text field to store the customer's name.
• order_date: A datetime field that automatically gets the current date and time whenever a new order is inserted. The CURRENT_TIMESTAMP keyword ensures this.

Example 2: Specifying a Different Default Value

CREATE TABLE tasks (
  task_id INTEGER PRIMARY KEY,
  description TEXT,
  due_date DATETIME DEFAULT datetime('now','localtime')
);

• task_id: An integer that acts as the primary key for each task.
• description: A text field to store the task description.
• due_date: A datetime field that by default gets the current date and time in the user's local time zone. This is achieved using the datetime('now','localtime') expression.

1. Triggers:

   • You can create a trigger that fires automatically whenever a new row is inserted.
   • The trigger can then execute a function to set the desired datetime value for the column.

   This approach gives you more control over the default value logic. You can define custom logic within the trigger function, potentially using database functions or external data sources.

2. Application-side Logic:

   • Instead of relying on the database for default values, you can handle it within your application code.
   • Before inserting a new row, your program can calculate the desired datetime value and include it in the INSERT statement.

   This method keeps the database schema simpler, but adds responsibility to your application for managing timestamps.

3. Pre-populated Default Value:

   • You can define a fixed default value (e.g., a specific date or a calculation) directly in the CREATE TABLE statement.
   • This approach might be useful if you have a standard default time for all entries.

   However, it becomes less flexible if the default datetime needs to change dynamically.

The best method depends on your specific needs and preferences.

Here's an example using a trigger (replace <your_logic_here> with your desired logic for setting the datetime):

CREATE TABLE events (
  event_id INTEGER PRIMARY KEY,
  title TEXT NOT NULL,
  start_datetime DATETIME DEFAULT (NULL)
);

CREATE TRIGGER set_start_datetime BEFORE INSERT ON events
FOR EACH ROW
BEGIN
  UPDATE events SET start_datetime = <your_logic_here>
  WHERE ROWID == NEW.ROWID;
END;