select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f
select cast (2000 as type of quint) from rdb$database select cast (2000 as int) from rdb$database.
Note: A NULL value is different from a zero value or a field that contains spaces.
Select char_length(cast('123456789 1' as varchar(10))) from rdb$database. Получаем: Exception ... string truncation Т.е. пробел мы обрезать можем, а другие символы нет. Так и должно быть или нет?
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...
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)...
The IS NOT NULL condition is used in SQL to test for a non-NULL value. It returns TRUE if a non-NULL value is found, otherwise it returns FALSE. It can be used in a SELECT, INSERT, UPDATE, or DELETE statement.
Union select null, null, null, null, null, null -- test all nulls --*/ ). A. DECLARE @ColumnDynamicSQL nvarchar(MAX)
R language supports several null-able values and it is relatively important to understand how these
5.5 How should NULL be defined on a machine which uses a nonzero bit pattern as the internal representation