If you have encountered the "Specified Key Was Too Long" error while working with MySQL, you are not alone. This error message can be frustrating and confusing, especially if you are not familiar with the underlying causes. In this guide, we will explain what this error means and provide a step-by-step solution to resolve it.
What is the 'Specified Key Was Too Long' Error?
The "Specified Key Was Too Long" error is a common error message that occurs when you try to add an index to a MySQL table. The error message usually reads as follows:
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
This error message indicates that the length of the index key exceeds the maximum length of 767 bytes allowed in MySQL. This limitation is due to the fact that MySQL uses a three-byte prefix for each index key. Therefore, the maximum length of the index key is 255x3 = 765 bytes.
Why Does the 'Specified Key Was Too Long' Error Occur?
The 'Specified Key Was Too Long' error occurs when you try to create an index on a column that exceeds the maximum length of 767 bytes. This usually occurs when you use a character set that requires more than one byte per character, such as UTF-8.
How to Fix the 'Specified Key Was Too Long' Error?
To fix the 'Specified Key Was Too Long' error, you need to reduce the length of the index key. You can do this by either shortening the length of the column or by changing the character set to one that requires fewer bytes per character.
Here are the steps to fix the error:
Identify the column that is causing the error.
Determine the current length of the column by running the following command:
SHOW CREATE TABLE table_name;
Modify the column to reduce its length. For example, if the column is currently defined as follows:
varchar(500) CHARACTER SET utf8mb4
You can reduce the length to 255 characters as follows:
varchar(255) CHARACTER SET utf8mb4
Re-run the command to create the index.
FAQ
Q1. What is the maximum length of an index key in MySQL?
The maximum length of an index key in MySQL is 767 bytes.
Q2. What character sets require more than one byte per character in MySQL?
Character sets such as UTF-8, UTF-16, and UTF-32 require more than one byte per character in MySQL.
Q3. Can I increase the maximum length of an index key in MySQL?
No, you cannot increase the maximum length of an index key in MySQL. It is a hard limit set by MySQL.
Q4. What is the default character set in MySQL?
The default character set in MySQL is utf8mb4.
Q5. What is the difference between utf8 and utf8mb4 in MySQL?
utf8mb4 is a superset of utf8 and supports the full range of Unicode characters, while utf8 only supports a subset of Unicode characters.