Substitutes the value specified in expression2 when expression1 evaluates to NULL.
isnull(expression1, expression2)
is a column name, variable, constant expression, or a combination of any of these that evaluates to a single value. It can be of any datatype, including unichar. expression is usually a column name. If expression is a character constant, it must be enclosed in quotes.
Returns all rows from the titles table, replacing null values in price with 0:
select isnull(price,0) from titles
isnull, a system function, substitutes the value specified in expression2 when expression1 evaluates to NULL. For general information about system functions, see “String functions”.
The datatypes of the expressions must convert implicitly, or you must use the convert function.
SQL92 – Compliance level: Transact-SQL extension.
Any user can execute isnull.
Function convert
