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
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qndbq7bbxilyCzFA') UNION ALL SELECT NULL,NULL,NULL,CONCAT(0x716e646271,IFNULL(CAST(grantee AS CHAR),0x20),0x716a716771),NULL FROM INFORMATION_SCHEMA.USER_PRIVILEGES#qjqgq.
Null is nothing but internal Pointer with value zero. So it is comparing two references having value zero. In fact object.ReferenceEquals(null, null) is always true because of this fact so you do not need the second check.
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. That's not my question.
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...
You'll have to explicitly state the condition on each column, so e.g. SELECT * FROM schedule WHERE id IS NOT NULL AND foo IS NOT NULL AND bar IS NOT NULL; -- and so on..
The reasoning is that a null means "unknown", so the result of any comparison to a null is also "unknown". So you'll get no hit on rows by coding where my_column = null. SQL provides the special syntax for testing if a column is null, via is null and is not null, which is a special condition to test for...
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