Products that use this syntax include Amazon Redshift and IBM DB2.Īmazon Redshift implements NVL() as an expression (as opposed to a function) that works identically to its COALESCE() expression. This syntax makes NVL() a synonym for COALESCE() (which returns the first non-NULL value of its arguments). With this syntax, we can provide any number of arguments, and NVL() will return the first non-NULL value. Other DBMSs use the following syntax: NVL( expression, expression. In some DBMSs (such as MariaDB) this makes NVL() a synonym for its IFNULL() function.ĭBMSs that use this syntax include Oracle, MariaDB, Exasol, Vertica, Snowflake, and IBM Informix. With this syntax, if expr1 is null, then expr2 is returned. The exact syntax will depend on your DBMS, but it will most likely fall under one of the following: NVL( expr1, expr2 ) The function allows us to replace any NULL values with another value. To see an example, suppose our test table now has the following structure and data: PersonIdĪnd we want to return each person’s first available contact data.Some DBMSs provide an NVL() function, which can be used when working with potentially NULL values. If all of them are null, then it returns null. , expression-n)Īnd this is how it works: It will accept any number of expressions or parameters (at least 2) and will return the first of them that is not null (evaluating from left to right). This is the syntax: COALESCE(expression-1, expression-2. Basically, it will return the first non-null value from a list of expressions provided. This function is actually part of the SQL standard, and thus is implemented in most DBMSs. NVL2 (accepts_calls, 'Call ' || NVL (work_phone ,mobile_phone ), 'Do not call' ) contact_method Suppose our test table is now like below, and that persons with the Accepts_Calls column null must not be contacted by phone: PersonId It is only used to determine whether expression2 must be returned, or expression3. Unlike the Oracle NVL function, the first expression in NVL2 is never returned. If it is null then expression3 is returned. If it is not null, then expression2 is returned. This is NVL2’s syntax: NVL2(expression1, expression2, expression3)Īnd this is how it works: Expression1 is the one that will be evaluated. There’s another function that can work in a very similar way ( DECODE), but we will talk about it some other day. Like Oracle NVL, this is another Oracle-specific function, which lets you decide which value to return, based on whether a specified expression is null or not. Suppose we have a simple table with this data: Person_Id In general, the return type will be that of the first expression. If expression1 is NULL then expression2 is returned. This is the syntax: NVL(expression1, expression2)Īnd this is how it works: If expression1 is not NULL, then expression1 is returned. Its purpose is to let you replace NULLs with another value or expression. This is an Oracle-specific function and is probably the most commonly used by Oracle developers. Also, using them correctly at work can make you look like a seasoned SQL developer □. Those functions are actually similar, but knowing what differentiates them from each other can help you use the correct one for a given situation. I have seen quite a few questions on internet forums and knowledge exchange sites about Oracle NVL, NVL2, and COALESCE functions for handling nulls, so I decided to write an article about them today.
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