Question

Assume that I have a table user_count defined as follows:

   id          primary key, auto increment
   user_id     unique
   count       default 0

What I want to do is increment count by one when an existing record of a user exists or else insert a new record.

Currently, I do it this way (in Python):

   try:
      cursor.execute("INSERT INTO user_count (user_id) VALUES (%s)", user.id)
   except IntegrityError:
      cursor.execute("UPDATE user_count SET count = count+1 WHERE user_id = %s", user.id)

And it can also be implement this way:

cursor.execute("INSERT INTO user_count (user_id) VALUES (user_id) ON DUPLICATE KEY UPDATE count = count + 1", user.id)

What’s the difference between these two ways, and which one is better?

Answer 1

The second one is a single SQL command which makes use of the feature that the database offers for solving exactly the problem you have here.

It’d use that as it should be faster and more reliable.

The first one is a fallback if that feature is not available (older database version?).