Why Does MySQL Throw a 'BLOB/TEXT Column Used in Key Specification Without a Key Length' Error?

MySQL database error: using BLOB/TEXT column without key length in key specification

When you encounter the error "Use of BLOB/TEXT column 'message_id' in key specification without key length", it is because MySQL cannot index the entire length of the BLOB or TEXT column. These columns require a specified key length to ensure uniqueness.

Error reason

This error mainly occurs when TEXT or BLOB types (including TINYBLOB, MEDIUMBLOB, LONGBLOB, TINYTEXT, MEDIUMTEXT and LONGTEXT) are specified as the primary key or used for indexing without specifying the key length.

Solution

To resolve this issue, there are several ways:

• Remove TEXT/BLOB column from key: Replace it with another indexable column.
• Set primary key on different field: If a suitable field exists, use it as the primary key instead.
• Limit column length: Convert the column to VARCHAR(n) and specify the maximum length. VARCHAR has a maximum length of 255 characters by default.

Other notes

• Incorrect VARCHAR length: Make sure the length of the VARCHAR column does not exceed 255 characters, otherwise MySQL will convert it to TEXT type, causing the same error.
• Existing Constraints: Problems may arise when changing column types if a TEXT or BLOB column is part of an existing unique constraint or index.

Reference

• MySQL Error 1170 (42000): Use of BLOB/TEXT column without key length in key specification

The above is the detailed content of Why Does MySQL Throw a 'BLOB/TEXT Column Used in Key Specification Without a Key Length' Error?. For more information, please follow other related articles on the PHP Chinese website!