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...
Note: A NULL value is different from a zero value or a field that contains spaces.
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 with, and shifted around the * to make sure the emails are displayed.
Coming to our discussion, NULL macro is defined as ((void *)0) in header files of most of the C compiler implementations. But C standard is saying that 0 is also a null pointer constant.
Существуют специальные операторы IS NULL и IS NOT NULL, которые позволяют производить сравнения с NULLами. IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.
I think your nitpicking is incorrect: (char*)NULL is a null pointer, but "\0" is an empty string. "" is also an empty string, as is "\0abc".
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When inner.value is marked as NOT NULL, all these queries are semantically equivalent and with proper indexing have similarly optimized execution plans in MySQL. Now, what if inner.value is not nullable and does contain some NULL values? Let's create some sample tables: Table creation details.
I do consider assignment statements and pointer variables to be among computer science's "most valuable treasures.". Donald Knuth, Structured Programming, with go to Statements.
В этой статье. Значение NULL в реляционной базе данных используется, если значение