When working with databases in MySQL, it’s common to need to combine data from multiple columns into a single column. This process is known as concatenation. In this tutorial, we’ll explore how to concatenate two columns into one while preserving the original column name.
To start, let’s consider a simple example where we have a table named customer with columns FIRSTNAME, LASTNAME, and several other columns. Our goal is to combine the FIRSTNAME and LASTNAME columns into a single column named FIRSTNAME.
One approach might be to use the CONCAT function in combination with the SELECT * statement, like this:
SELECT *, CONCAT(FIRSTNAME, ',', LASTNAME) AS FIRSTNAME FROM `customer`;
However, this will result in two columns with the name FIRSTNAME: one containing the original values and another containing the concatenated values.
To avoid this issue, we need to explicitly specify the columns we want to include in our query instead of using SELECT *. We can do this by listing all the column names individually:
SELECT SOME_OTHER_COLUMN, CONCAT(FIRSTNAME, ',', LASTNAME) AS FIRSTNAME FROM `customer`;
However, if our table has many columns (e.g., 40 or more), specifying each one manually can be tedious and prone to errors.
A more efficient approach is to use a combination of the CONCAT function and table aliasing. We can select all columns from the table using the * wildcard, but we need to alias the table to avoid conflicts with column names:
SELECT CONCAT(c.FIRSTNAME, ',', c.LASTNAME) AS FIRSTNAME,
c.*
FROM `customer` c;
In this query, the second occurrence of the FIRSTNAME column will be automatically aliased as FIRSTNAME_1, allowing us to safely address our customized FIRSTNAME column.
Alternatively, if you only need a few columns, it’s better to specify them explicitly:
SELECT CONCAT(FIRSTNAME, ' ', LASTNAME) AS FIRSTNAME FROM customer;
It’s also worth considering using a more descriptive alias for the concatenated column, such as FULL_NAME, to improve readability and avoid confusion:
SELECT CONCAT(FIRSTNAME, ' ', LASTNAME) AS FULL_NAME FROM customer;
In summary, when concatenating columns in MySQL while preserving the original column name, it’s essential to either specify all columns explicitly or use table aliasing with the CONCAT function. This ensures that you get only one column with the concatenated values and avoid conflicts with original column names.
Best practices:
- Avoid using
SELECT *whenever possible, as it can lead to unexpected results and make your queries harder to maintain. - Use descriptive aliases for concatenated columns to improve readability.
- Consider specifying all column names explicitly if your table has a small number of columns.