Oracle SQL Study Guide 2026

A deadlock occurs when two or more transactions each hold locks that the other needs, creating a circular wait that Oracle detects and resolves by rolling back one transaction.

The `<ANY` operator in SQL subqueries means that the value being compared is less than at least one of the values returned by the subquery. This effectively means the value is less than the maximum value present in the subquery's result set. For example, `salary < ANY (SELECT salary FROM employees WHERE department_id = 10)` would return employees whose salary is less than the highest salary in department 10.

NULLIF returns NULL when both arguments are equal; otherwise it returns the first argument.

TRUNC without a second argument removes all decimal places, returning the integer portion 45 without rounding.

READ COMMITTED prevents dirty reads because queries only see data that was committed before the query started, never uncommitted data from other transactions.

SUM() used as an analytic function with OVER (ORDER BY column) computes a cumulative running total up to each row.