Database Interview

Inner Join vs Outer Join

An INNER JOIN returns only the rows that have matching values in both tables, while an OUTER JOIN (LEFT, RIGHT, or FULL) returns matched rows plus unmatched ro…

What is a Composite Key?

A composite key is a primary key made up of two or more columns that, together, uniquely identify a row, even though no single column among them is unique on i…

HAVING vs WHERE Clause

WHERE filters individual rows before any grouping or aggregation happens, while HAVING filters groups after GROUP BY has aggregated them, so HAVING is the only…

What is a Cursor in SQL?

A cursor is a database object that lets a program process a query result set one row at a time, instead of the usual set-based operation that acts on all match…

CHAR vs VARCHAR

CHAR is a fixed-length string type that always stores and pads to its declared length, while VARCHAR is a variable-length type that stores only the actual char…