I have a project that can use either SQL Server or MS Access as the data store. In one SELECT statement, I must perform a COALESCE operation on a single column and a single value, like this:
SELECT COALESCE([Amount], 0) FROM PaymentsDue;
I would like to write a single SQL statement that will execute correctly in both SQL Server and MS Access. The SQL Server version that is of immediate interest is 2008, although a solution applicable across versions would be preferred.
Earlier today, someone was able to show me an SQL trick that allowed me to use a single SELECT statement to effectively CAST a DATETIME to DATE. I was wondering if anyone has a similar trick to perform a COALESCE (eg, IFNULL or NZ) operation in a way that can be applied to both SQL Server and MS Access?
The SQL server's Coalesce function is used to handle the Null values. The null values are replaced with user-defined values during the expression evaluation process. This function evaluates arguments in a particular order from the provided arguments list and always returns the first non-null value.
You can use the Nz function to return zero, a zero-length string (" "), or another specified value when a Variant is Null. For example, you can use this function to convert a Null value to another value and prevent it from propagating through an expression. Syntax. Nz ( variant [, valueifnull ] )
The COALESCE function returns the first non-NULL value from a series of expressions. The expressions are evaluated in the order in which they are specified, and the result of the function is the first value that is not null.
COALESCE is useful when you have unknown number of values that you want to check. IFNULL is useful when you select columns and know that it can be null but you want to represent it with a different value. Therefore, the two functions are vastly different.
Create a custom public function in a module.
Public Function COALESCE(InputValue, ValueIfNull)
COALESCE = nz(InputValue, ValueIfNull)
End Function
Add in error handling, etc., make improvements.
Now, you would be able to use the COALESCE
function in MS Access and SQL.
I don't think there is any syntax that functions the same on both platforms.
Note Nz()
is only available when using the Access user interface.
Here are a couple of suggestions that can be transformed to COALESCE
fairly easily, though repeating the column is a pain:
Sample 1:
SELECT IIF([Amount] IS NULL, 0, [Amount]) FROM PaymentsDue;
Sample 2:
SELECT SWITCH([Amount] IS NULL, 0, TRUE, [Amount]) FROM PaymentsDue;
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