NVLexpr1

NVLexpr1 is a term used in some documentation and code samples to denote the first operand of a null-value replacement function in SQL-style expressions. In many database systems, the function NVL takes two arguments: NVLexpr1 and NVLexpr2. The function evaluates NVLexpr1; if its value is not null, that value is returned; otherwise NVLexpr2 is evaluated and returned. The designation NVLexpr1 is not part of the formal SQL standard; rather, it is a descriptive label used when explaining or teaching the concept of a null-handling expression that substitutes a non-null value for a null.

In practice, NVLexpr1 is typically an expression such as a column reference or an expression that may yield NULL. The second argument, NVLexpr2, provides the replacement value and may be a constant or another expression. The resulting data type is determined by the engine’s type-coercion rules, commonly matching the type of NVLexpr1 with an implicit cast of NVLexpr2.

NVLexpr1 is widely associated with Oracle’s NVL function, where a similar construct is written as NVL(expr1, expr2). Many databases offer equivalent functionality under COALESCE or ISNULL; COALESCE is standard SQL and can take more than two arguments, while NVL is two-argument and non-standard.

Examples: NVL(salary, 0) returns salary when not null, otherwise 0. NVL(customer_name, 'Unknown') ensures a string is always returned.

See also: COALESCE, ISNULL, NULL handling, Oracle SQL, SQL standard.