Sql server where isnull function

Company Questions. Artificial Intelligence. Cloud Computing. Data Science. Angular 7. Machine Learning. Data Structures. Operating System. Computer Network. Compiler Design. Computer Organization. Discrete Mathematics. Ethical Hacking. Computer Graphics. Software Engineering. Web Technology. Cyber Security. Suppose we want to perform sum of EmployeeSalary present in Employee table.

You can visualize it with the following screenshot. We use it to replace NULL values with a specific value. In the second part, we can see the employee having a NULL salary.

If we have multiple data types in an expression, SQL Server converts the lower precedence data types into a higher precedence data type. In the following image, we can all possible implicit and explicit allowed data type conversions. Image Reference: Microsoft Docs. In the above table, we can see that the precedence of INT is higher than the timestamp data type. Execute the following query. As said above, a good rule of thumb is to try and avoid using functions in a WHERE clause as it limits the query engine's ability to use an index effectively.

But this then begs the question: What do we do if we want to search for some particular value as well as NULL? As you can see from the query plan below this will use the index but has to perform a scan of the entire index as was happening in the update example.

You can use the ISNULL function to specify a hard-coded value or even use another column in the table for the join condition. Below is an example that shows how you can return the personal address of a person and if that does not exist return their business address. A good example of this is using our Person table structure from above. We know from before that you do not have to specify a businessaddressid as shown below.

If you were to write a query to concatenate all the name related columns to display the full name you could do this but it would require manually adding the ISNULL function around every column that is nullable as follows.

As you can see this is quite cumbersome and if you are doing the operation a lot a much simpler approach would be to add the following persisted computed column to the table. Related Articles. Different ways to get random data for SQL Server data sampling.

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