How to resolve ambiguous column names when retrieving results?

When executing SQL queries in PHP and encountering ambiguous column names, you can use table aliases to specify which table the column belongs to. For example, instead of just selecting "column_name", you would select "table_alias.column_name" in your query. For instance, if you have two tables, "table1" and "table2" with a column named "id", you could use the aliases "t1" and "t2" to specify which "id" column you are referencing in your query. Alternatively, you can use fully qualified table names (e.g., table1.id) without creating aliases.

Note: Use table aliases to shorten table references in complex queries, and column aliases to rename output columns for clarity.

SELECT t1.id, t2.id FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

You can also use the AS keyword to assign a column alias.

SELECT table1.id AS t1_id, table2.id AS t2_id FROM table1 JOIN table2 ON table1.id = table2.id;

It's also possible to use the USING clause to specify which column to join on when using JOIN. Unlike ON, which allows custom conditions, USING is a shorthand for equi-joins on columns with identical names in both tables. In most SQL dialects, USING merges the joined column into a single output column, so you should reference it without a table prefix.

SELECT id FROM table1 t1 JOIN table2 t2 USING (id);