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.
Note: A NULL value is different from a zero value or a field that contains spaces.
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...
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.
R language supports several null-able values and it is relatively important to understand how these values behave, when making data pre-processing and
ID in both tables will never be NULL. It IS possible that one of the tables may have ID values that are NOT in the other table.
NULL handling in the Oracle database is even more special. Contrary to common believe, using
The null character (also null terminator or null byte), abbreviated NUL or NULL, is a control character with the value zero. It is present in many character sets, including ISO/IEC 646 (or ASCII)...
Instead, use WHERE IS NULL or WHERE IS NOT NULL. The definitive guide for data professionals.
The IS NOT NULL condition is used in SQL to test for a non-NULL value.