Union select null, null, null, null, null, null, null from information_schema.tables. for a small database containing three tables. this instruction is used in sql injection I tried it and it worked but I didn't really know how it works can somebody help me...
11223344) UNION SELECT NULL,NULL,NULL,NULL WHERE 1=2 –- Если нет ошибки, значит синтаксис верный, т.е. используется MS SQL Server.
UNION ALL SELECT NULL, *, NULL, NULL FROM email. I understand what this does and why; the hacker needs to create a query that has the same number of columns as the query it's being merged
Как и в случае с обычными переменными, указатели не инициализируются при создании. Если значение не было присвоено, то указатель по умолчанию будет указывать на любой адрес, содержимым которого...
If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.
At the very high level, we can think of NULL as a null pointer which is used in C for various purposes.
Note: A NULL value is different from a zero value or a field that contains spaces.
I've tried setting the pointer to null but keep getting a segmentation error.
Suppose that the "UnitsOnOrder" column is optional, and may contain NULL values. Look at the following SELECT statement: SELECT ProductName, UnitPrice * (UnitsInStock + UnitsOnOrder) FROM Products; In the example above, if any of the "UnitsOnOrder" values are NULL, the result will be NULL.
Существуют специальные операторы IS NULL и IS NOT NULL, которые позволяют производить сравнения с NULLами.