It is not possible to test for NULL values with comparison operators, such as =,. The following SQL lists all customers with a NULL value in the Address field:. According to the three-valued logic of SQL , the result of null = null is not true but unknown. What do you get when you compare a value to NULL ? Tests with null values are always false in SQL , except IS NULL or IS NOT NULL. SQL comparisons 5 Antworten 8. How to compare values which may both be null.
Weitere Ergebnisse von stackoverflow. Compare possible null values in one query - Database. WITH TIES but this works only because NULL values are treated as the lowest in SQL Server. SELECT TOP (1) WITH TIES t. When testing for a NULL value, IS NULL is the recommended comparison operator to use in SQL. We use IS NULL instead of = for comparison with NULL.
This is because there are many RDBMSs that become UNKNOWN if you compare null. Do you ever compare the values of a lot of columns in two tables? SqlTypes as compared with the way it . To test for nulls , use only the comparison conditions IS NULL and IS NOT NULL. SQL allows queries that check whether an attribute value is NULL.
Rather than using = or to compare an attribute value to NULL , SQL uses IS and IS NOT. The Three-Valued Logic of SQL has its uses but can cause.
