Should I Always Fully Qualify Column Names In SQL?

Question

Out of interest when working with SQL statements should I always use the fully qualifed column name (tablename.columnname) even if only working with one table e.g.

Answer 1

I generally follow these rules:

When using a single table, it is not necessary to use the table name prefix:

SELECT col1, col2 FROM table1

For multiple tables, use the full table name. Aliases can be confusing, especially when doing multiple joins:

SELECT table1.col1, table2.col2 FROM table1 INNER JOIN table2 on 
            table1.id = table2.id

I see many developers using table aliases, but particularly in large projects with multiple developers, these can become cryptic. A few extra keystrokes can provide a lot more clarity in the code.

If may, however, become necessary to use a column alias when columns have the same name. In that case:

    SELECT table1.col1, table2.col1 as table2_col1 FROM table1 
            INNER JOIN table2 on 
            table1.id = table2.id