What is the difference between insert, update and replace?

In database operations, insert, update, and replace are commands used to modify data, but they serve different purposes:

1. Insert: Adds a new record to a table. If the record already exists (based on a unique key), it will fail unless the table allows duplicates.

   • Example: INSERT INTO users (id, name) VALUES (1, 'Alice');
     If id=1 doesn’t exist, it adds Alice; otherwise, it raises an error.

2. Update: Modifies existing records that match a condition. If no records match, nothing happens.

   • Example: UPDATE users SET name = 'Bob' WHERE id = 1;
     Changes Alice’s name to Bob if id=1 exists.

3. Replace: First attempts to delete the existing record (if it exists) and then inserts a new one. It’s like a combination of delete + insert.

   • Example: REPLACE INTO users (id, name) VALUES (1, 'Charlie');
     If id=1 exists, it deletes the old record and inserts Charlie; if not, it just inserts Charlie.

Use Cases:

• Use insert for adding new data.
• Use update for modifying existing data.
• Use replace when you want to overwrite a record entirely (e.g., syncing data where the latest version should always replace the old one).

In cloud database services like Tencent Cloud Database (TDSQL), these operations are supported with high performance and reliability. For example, TDSQL’s MySQL-compatible instances allow efficient use of INSERT, UPDATE, and REPLACE for managing data at scale.