Sql eliminate null values

Let's try executing some queries using NULL values as parameters in aggregate functions. Let's try using the COUNT distinct column aggregate function, which counts all the different values in a column. How does this treat NULL values? The query returned a "3", but there are four different salaries: , , , and NULL. Again, we can conclude that the NULL is not included in the resulting value. The conclusion is that averages are only calculated using non-NULL values.

For all set functions that specify a column name, the following process takes place behind the scenes: The search expression the WHERE clause is applied. The value expression in this example is simply a column name - region. The order in which SQL performs the steps in aggregate calculations can have implications for your results.

There are a couple of "gotcha's" concerning the AVG function. The first "gotcha" is that NULLs are excluded, as with other set functions, so your answer may not be what you expect. The second "gotcha" is that, by definition, AVG returns a number of the same scale as the column it is performed on.

The following query divides the sum of the reportsto column by the count of non-NULL rows. With larger numbers and more rows the difference is more pronounced. Consider an example of calculating the average payroll for a department. Now let's say that we hire a new guy, but his weekly pay has not been put into the system yet. That depends entirely on your objectives and corporate policies.

If you ignore NULLs in calculating averages, use that same methodology every time; otherwise your results will not be comparable from year to year, quarter to quarter or even day to day. In our examples, the averages we received were calculated and returned with the same scale digits after the decimal point as the column; in this case the column is an INT data type, so no decimals were returned.

Since AVG calculates using the same scale as the column data type, our INT column average is calculated with no decimal places. In the second example, we CAST the SUM of the reportsto column to a floating point type, and then divided; so we didn't lose any digits after the decimal point in the calculation. This is particularly important to note in financial and scientific calculations, where the scale is particularly important to our calculations. Gotcha: AVG also uses the precision total number of digits and scale number of digits after the decimal point of the column you are performing the AVG on.

Query to delete null or empty values from datatable in sql server By: Suresh Dasari Jul 9, Introduction :. Here I will explain how to write a query to delete null or empty values from datatable in SQL Server. Description :. For that first design one table UserInfo in database and enter data like as shown below. Query to get records without null or empty values.

If we want to get the records without null or empty values we need to write query like as shown below. Query to get records with null or empty values. In some cases, the ISNULL function is used with the where condition but this usage method may lead to use indexes inefficiently.

However, this query cannot use the created non-clustered index so it will read all index pages and then return the appropriate rows. To eliminate this situation, we can make a little code modification in the query so that the query optimizer can use the indexes more efficiently. The following query returns some rows as like the previous one but it uses the indexes more efficiently.

FROM Person. USE [ AdventureWorks ]. ON [ Person ]. Author Recent Posts. Esat Erkec.