DefineR

Definer is a concept used in relational database systems to designate the security context under which certain database objects execute. When a routine or object is defined with a definer, it is the privileges of that defined user, rather than the privileges of the user invoking the object, that are used during access checks. This separation between the definer and the invoker helps control how privileges are applied when routines, views, or similar constructs are executed.

In MySQL, the DEFINER clause is used with stored routines (procedures and functions) and views to specify which account’s privileges should be employed when the object runs. The SQL SECURITY setting further controls whether access checks are performed using the definer’s privileges (SQL SECURITY DEFINER) or the caller’s privileges (SQL SECURITY INVOKER). If a definer is not explicitly specified, the object inherits the creator’s account as the default definer. Triggers generally execute with the privileges of the invoking user rather than a separate definer.

In PostgreSQL, the corresponding mechanism is implemented at the function level with the SECURITY DEFINER and SECURITY INVOKER modifiers. A function declared SECURITY DEFINER runs with the privileges of the function’s owner, regardless of who calls it, while SECURITY INVOKER uses the caller’s privileges. The owner and the security setting together determine which privileges are applied during function execution.

Security considerations are central to the use of definers. Definer-based execution can enable privilege escalation if a high-privilege definer is compromised or misused. Best practices include limiting definer rights, preferring SECURITY INVOKER when possible, and carefully auditing and restricting the objects that use elevated privileges.