How to Concatenate Strings in SQL for URL Construction

To write an SQL query with a return value of 'http://localhost/blah/' plus the value of the field 'url_field', you can use string concatenation in your query.

Here's an example of how you can do it in different databases:

MySQL:

SELECT CONCAT('http://localhost/blah/', url_field) AS full_url
FROM your_table;

PostgreSQL:

SELECT 'http://localhost/blah/' || url_field AS full_url
FROM your_table;

Oracle:

SELECT 'http://localhost/blah/' || url_field AS full_url
FROM your_table;

SQL Server:

SELECT 'http://localhost/blah/' + url_field AS full_url
FROM your_table;

Replace 'your_table' with the actual name of your table, and 'url_field' with the actual name of the field/column containing the URLs. The result will be a new column called 'full_url' which combines the fixed string and the value of the 'url_field'.