SQLite Conditional Insert

Here's the basic syntax:

INSERT OR IGNORE INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);

• value1, value2, ...: These are the values you want to insert into the corresponding columns.
• column1, column2, ...: These are the columns in the table where you want to insert the data.
• table_name: This is the name of the table you want to insert the data into.
• INSERT OR IGNORE: This is the core of the statement. It tells SQLite to insert the new row if it doesn't exist. If a row with the same unique identifier already exists, SQLite will ignore the INSERT statement and no error will be raised.

Example:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT,
    email TEXT UNIQUE
);

INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]');
INSERT OR IGNORE INTO users (name, email) VALUES ('Jane Smith', '[email protected]');
INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]'); -- This will be ignored

In this example, the first two INSERT statements will successfully add new rows to the users table. However, the third INSERT statement will be ignored because a row with the same email address already exists.

Key points to remember:

• The statement will not raise an error if a duplicate row is found. Instead, it will simply ignore the INSERT operation.
• It is especially useful when you are inserting data from external sources that may contain duplicates.
• The "INSERT IF NOT EXISTS" statement is a convenient way to prevent duplicate data in your SQLite database.

Example Codes for "INSERT IF NOT EXISTS" in SQLite

Python Example using the sqlite3 module:

import sqlite3

conn = sqlite3.connect('mydatabase.db')
c = conn.cursor()

# Create a table if it doesn't exist
c.execute('''CREATE TABLE IF NOT EXISTS users (
                id INTEGER PRIMARY KEY,
                name TEXT,
                email TEXT UNIQUE
              )''')

# Insert data if it doesn't exist
c.execute('''INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]')''')
c.execute('''INSERT OR IGNORE INTO users (name, email) VALUES ('Jane Smith', '[email protected]')''')

# Try to insert a duplicate email
c.execute('''INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]')''')

conn.commit()
conn.close()

Java Example using the sqlite-jdbc driver:

import java.sql.*;

public class SQLiteExample {
    public static void main(String[] args) {
        try {
            Class.forName("org.sqlite.JDBC");
            Connection connection = DriverManager.getConnection("jdbc:sqlite:mydatabase.db");   
            Statement statement = connection.createStatement();   

            // Create a table if it doesn't exist
            statement.executeUpdate("CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY, name TEXT, email TEXT UNIQUE)");

            // Insert data if it doesn't exist
            statement.executeUpdate("INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]')");
            statement.executeUpdate("INSERT OR IGNORE INTO users (name, email) VALUES ('Jane Smith', '[email protected]')");

            // Try to insert a duplicate email
            statement.executeUpdate("INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]')");

            connection.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

C# Example using the System.Data.SQLite NuGet package:

using System.Data.SQLite;

namespace SQLiteExample {
    class Program {
        static void Main(string[] args) {
            using (var connection = new SQLiteConnection("Data Source=mydatabase.db;Version=3;")) {
                connection.Open();

                using (var command = connection.CreateCommand()) {
                    command.CommandText = "CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY    KEY, name TEXT, email TEXT UNIQUE)";
                    command.ExecuteNonQuery();

                    command.CommandText = "INSERT OR IGNORE INTO users (name, email) VALUES ('John Doe', '[email protected]')";
                    command.ExecuteNonQuery();

                    // ... other INSERT OR IGNORE statements
                }
            }
        }
    }
}

Using a SELECT Statement and IF EXISTS

• Logic: First, check if a row with the specified unique identifier already exists using a SELECT statement. If it does, skip the insertion. If not, proceed with the insertion.

SELECT EXISTS (SELECT 1 FROM users WHERE email = '[email protected]');

If the result is 0, the row doesn't exist, and you can proceed with the insertion.

Using a Transaction and Rollback

• Logic: Begin a transaction, attempt to insert the row, and then check for an error. If an error occurs (likely due to a unique constraint violation), rollback the transaction. Otherwise, commit it.

BEGIN TRANSACTION;
INSERT INTO users (name, email) VALUES ('John Doe', '[email protected]');
IF EXISTS (SELECT 1 FROM users WHERE email = '[email protected]') THEN
  ROLLBACK;
ELSE
  COMMIT;
END IF;

Using a MERGE Statement (SQLite 3.28 or later)

• Logic: The MERGE statement is a more concise way to perform conditional inserts and updates. It can be used to insert a row if it doesn't exist or update it if it does.

WITH new_user AS (
  SELECT 'John Doe' AS name, '[email protected]' AS email
)
MERGE INTO users USING new_user ON users.email = new_user.email
WHEN MATCHED THEN UPDATE SET users.name = new_user.name
WHEN NOT MATCHED THEN INSERT (name, email) VALUES (new_user.name, new_user.email);

Choosing the Right Method:

• MERGE: A powerful option for more complex scenarios involving both inserts and updates.
• Transaction and Rollback: Provides more granular control over the insertion process, but can be slower.
• SELECT and IF EXISTS: Can be useful if you need to perform additional checks or actions before or after the insertion.
• INSERT OR IGNORE: Generally the most efficient and convenient option, especially for simple cases.