How do you compare NULL values?
In SQL Server, NULL value indicates an unavailable or unassigned value. The value NULL does not equal zero (0), nor does it equal a space (‘ ‘). Because the NULL value cannot be equal or unequal to any value, you cannot perform any comparison on this value by using operators such as ‘=’ or ‘<>’.
How do I compare NULL values in SQL?
Say you have a table with a NULLable column type, and you want to find rows with a NULL value in that column. Since you can’t use a equality operator in the WHERE clause (remember, NULL values can’t be equated or compared), the right way to compare NULL values is to use the IS and IS NOT operators.
Why are NULL values a problem?
The NULL value can cause problems when selecting data. However, because when comparing an unknown value to any other value, the result is always unknown and not included in the results. You must use the IS NULL or IS NOT NULL operators to check for a NULL value.
How do you add null values?
You also can specify the NULL keyword in the VALUES clause to indicate that a column should be assigned a NULL value. The following example inserts values into three columns of the orders table: INSERT INTO orders (orders_num, order_date, customer_num) VALUES (0, NULL, 123);
Is the result of comparing anything to Null always null?
The result of comparing anything to NULL, even itself, is always, always NULL. A comparison to NULL is never true or false. Since NULL can never be equal to any value, it can never be unequal, either. Sometimes people have difficulty understanding why a comparison to NULL can never be either true or false. Here’s an informal proof that may help:
Why is null not equal to anything in SQL?
Not only is NULL not equal to anything, it’s also not unequal to anything. This is where the language is confusing. The truth is, saying anything with the words “equal” or “not equal” is a trap when discussing NULL s, because there is no concept of equality or inequality, greater than or less than with NULLs.
How to compare values which are both null in T-SQL?
The idea is to use short circuit in predicates to make sure the equal operator (=) is used only with non-null values, otherwise null would propagate up in the expression tree. You could use SET ANSI_NULLS in order to specify the behavior of the Equals (=) and Not Equal To (<>) comparison operators when they are used with null values.
Is it efficient to use equal operator with NULL values?
Yes, it is. However it’s efficient since it doesn’t call any function. The idea is to use short circuit in predicates to make sure the equal operator (=) is used only with non-null values, otherwise null would propagate up in the expression tree.