Understanding Numeric Column Transformation in MySQL

MySQL often transforms long integers to unexpected values when inserted into shorter columns. Instead of truncating, MySQL adjusts the stored value. This behavior is attributed to the integer overflow mechanism.

For example, consider a column named some_number with a length of 10. When a number exceeding this length (e.g., 715988985123857) is inserted, it is transformed into 2147483647.

The Overflow Mechanism

According to the MySQL documentation, integer overflow occurs when the result of a calculation exceeds the maximum allowed value for the data type. In this case, the maximum value for a 10-bit integer is 2147483647.

Formula for Calculated Result

The transformation follows a specific formula:

Result = Number % (2^Bits) - 1

where:

• Number is the original number being inserted
• Bits is the number of bits in the destination column

In our example, Number is 715988985123857 and Bits is 10, resulting in:

2147483647

BigInt vs. Int

To avoid integer overflow, use a bigint data type for larger integers. BigInt can store values up to 2^63-1, preventing truncation or transformation issues.