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24 sty 2013 · A column can only return one data type - DATETIME != string/VARCHAR. If you want a zero length string in the event of the value being NULL, you have to explicitly change the data type, using CAST/CONVERT to change the non-NULL value to a VARCHAR/etc data type.
17 lis 2015 · If you're checking whether or not the value is NULL, there is no need to convert it to a date, unless you wanted to return a date value (which you don't seem to). Instead, use: SELECT ISNULL( DOB , '') Which will return '' if the value is NULL. A NULL date is NULL (no value).
4 sty 2011 · If you use NULL you have to do WHERE columnX=<searchvalue> or (columnX is NULL and searchvalue is NULL). The second, more complicated logic, is indeed what you have to do in Oracle, as NULL and '' are the same thing there.
The SQL Server ISNULL() function lets you return an alternative value when an expression is NULL: SELECT ProductName, UnitPrice * (UnitsInStock + ISNULL(UnitsOnOrder, 0)) FROM Products;
It is important to understand that a NULL column value is different than having a blank (empty string) or 0 value in a column. eg. ' ' or (empty string) <> NULL, 0 <> NULL. Let’s take a look at a few examples to illustrate these points.
To check for null and empty: coalesce(string, '') = '' To check for null, empty and spaces (trim the string) coalesce(TRIM(string), '') = ''
6 cze 2024 · MS SQL provides a function ISNULL to check for null values: SELECT id, name FROM Department WHERE ISNULL (code, '') = '' OR TRIM (code) = ''; The ISNULL function in MS SQL takes two arguments: the first is a value or column name, and the second is the default value if the first argument is null.
