How to Resolve 'Unknown Column' Error When Using CONCAT in MySQL WHERE Clause?

MySQL Select with CONCAT Condition: Resolving "Unknown Column" Error

When using the CONCAT function to concatenate multiple columns in a MySQL query, you may encounter an "unknown column" error if you try to reference the concatenated string as a column within the WHERE clause.

To resolve this issue, you have two options:

1. Repeat the CONCAT Expression:

   This involves repeating the CONCAT expression within the WHERE clause.

   SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
   FROM users
   WHERE CONCAT(firstname, ' ', lastname) = "Bob Michael Jones"

2. Wrap the Query:

   This method involves wrapping the original query in a subquery and then referencing the concatenated string as a column in the WHERE clause of the outer query.

   SELECT * FROM (
     SELECT neededfield, CONCAT(firstname, ' ', lastname) as firstlast 
     FROM users) base 
   WHERE firstLast = "Bob Michael Jones"

By implementing either of these options, you can concatenate multiple columns and use the concatenated string as a search condition in your MySQL query.

The above is the detailed content of How to Resolve 'Unknown Column' Error When Using CONCAT in MySQL WHERE Clause?. For more information, please follow other related articles on the PHP Chinese website!