select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f from table3.
...FROM (SELECT 1 UNION SELECT null UNION SELECT !1)x GROUP by CONCAT.
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...
union all select null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null
Note: A NULL value is different from a zero value or a field that contains spaces.
NULL handling in the Oracle database is even more special.
Специальное значение NULL означает отсутствие данных, констатацию того факта, что значение неизвестно. По умолчанию это значение могут принимать столбцы и переменные любых типов, если только на них не наложено ограничение NOT NULL.
NULL is special in SQL. NULL indicates that the data is unknown, inapplicable or even does not exist.
The IS NOT NULL condition is used in SQL to test for a non-NULL value.
R language supports several null-able values and it is relatively important to understand how these values behave, when making data pre-processing and