IFNULLexpr1

IFNULLexpr1 is a notation encountered in SQL documentation and examples to refer to the first argument of the IFNULL function. It is not a standalone function or keyword in SQL itself; rather, it serves as a placeholder that viewers replace with a concrete expression, such as a column name or a computed value. The concept is used to illustrate how IFNULL operates without tying the discussion to a specific dataset.

In standard usage, IFNULL takes two arguments: an expression to test for NULL (represented by expr1 in sample syntax), and a replacement expression (expr2) to return when the first argument is NULL. The general rule is that IFNULLexpr1,expr2 yields expr1 when expr1 is not NULL; otherwise it yields expr2. The return type is typically compatible with the types of expr1 and expr2, and if both are NULL, the result is NULL.

Examples help clarify the idea. A typical query might be: SELECT IFNULL(salary, 0) FROM employees; here salary is the expr1 placeholder, and 0 is expr2. If salary is NULL for a row, the query returns 0; otherwise it returns the actual salary value. Another common pattern is: SELECT IFNULL(last_name, 'Unknown') FROM customers.

Notes and compatibility: IFNULL is a function available in some SQL dialects (notably MySQL and SQLite). Other systems use COALESCE or NVL for similar behavior. When documenting code, IFNULLexpr1 consistently refers to the first argument, emphasizing the NULL-check logic rather than a fixed identifier.