How to Prevent Duplicate Entries in MySQL Tables Using Triggers?

How to Handle Duplicate Entries in MySQL Triggers

Background:
In this scenario, the goal is to ensure that combinations of unique URLs and parameter strings maintain uniqueness in a MySQL table. However, the parameter string length exceeds the key length limit for MySQL, preventing the use of unique key constraints.

Trigger Implementation:

To address this issue, triggers can be employed to enforce the uniqueness constraint. The trigger code checks for duplicate entries before allowing the insert operation.

Handling Duplicate Entries:

The trigger code includes two critical portions:

1. Abort/Raise Exception to C#:
   To throw an exception when a duplicate entry is detected, the following code can be added:

2. Allow Insert:
   If no duplicate exists, the insert operation is allowed by leaving the ELSE block empty.

Improved Solution:

A more advanced solution utilizes MySQL's SIGNAL function, which allows for custom error messages and trapped exceptions. This approach is outlined in the provided code:

This method returns a custom error message that can be intercepted and handled in the C# code.

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