When INSERT OR IGNORE Isn't Enough: Alternative Methods for Conflict Resolution in SQLite

• Unique Constraints: INSERT OR IGNORE only works when there's a unique constraint defined on the table you're inserting into. This constraint can be a primary key, a unique index, or a combination of columns with a UNIQUE clause.

  For example, if your table has a column named name with a UNIQUE constraint, then INSERT OR IGNORE will only insert a new row if the name value doesn't already exist in the table.

Here's an alternative approach to consider:

• ON CONFLICT Clause: SQLite provides a more robust option called ON CONFLICT. This clause allows you to specify what action to take when a conflict occurs during an insert or update operation. You can choose to ignore (similar to INSERT OR IGNORE), rollback, abort, replace, or even define a custom behavior.

Example Codes:

This example creates a table with a unique constraint on the name column. Then, it inserts two rows with the same name, demonstrating how INSERT OR IGNORE only inserts the first occurrence.

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

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

-- This will only insert one row with name 'Alice'

Potential Silent Failure:

This example shows how INSERT OR IGNORE might silently fail if there's a constraint violation other than uniqueness.

CREATE TABLE products (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  name TEXT,
  stock INTEGER NOT NULL -- This is a NOT NULL constraint
);

INSERT OR IGNORE INTO products (name, stock) VALUES ('Widget', NULL);

-- This insertion might silently fail because of the NOT NULL constraint violation

Using ON CONFLICT Clause (Update on Conflict):

Here, we use the ON CONFLICT clause to update an existing row's stock instead of silently failing or ignoring the insert.

CREATE TABLE products (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  name TEXT,
  stock INTEGER NOT NULL
);

INSERT INTO products (name, stock) VALUES ('Widget', 5)
ON CONFLICT(name) DO UPDATE SET stock = stock + excluded.stock;

-- This will insert the first row and on subsequent inserts with the same name, update the stock quantity

1. Separate INSERT and Check:

This approach involves two separate statements:

• An INSERT statement to attempt inserting the new row.
• A SELECT statement (or any other logic) to check if the insertion was successful (based on the number of rows affected).

Here's an example:

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

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

-- Check if the insert was successful (should return 1)
SELECT ROWCOUNT(); 

-- If successful, proceed with further logic.

1. Transaction with Conditional Insert:

This utilizes a transaction to ensure data consistency.

• Begin a transaction.
• Attempt the INSERT statement.
• If a constraint violation occurs (causing an error), rollback the transaction.
• If successful, commit the transaction.

BEGIN TRANSACTION;

INSERT INTO products (name, stock) VALUES ('Widget', NULL);

-- Check for errors after insert attempt
IF NOT (SELECT changes() > 0) THEN
  ROLLBACK TRANSACTION;
ELSE
  COMMIT TRANSACTION;
END IF;

1. REPLACE Clause (with Caution):

Use with caution! Unlike INSERT OR IGNORE, REPLACE completely replaces an existing row if a conflict occurs based on the unique constraint. This can lead to data loss if you're not careful.

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

INSERT OR REPLACE INTO users (name) VALUES ('Alice');
INSERT OR REPLACE INTO users (name) VALUES ('Bob');

-- This will replace the existing 'Alice' row with 'Bob'