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.
Then in the second table I have select ..., null as opt from... I know that I could have an empty string with '' as
select cast (2000 as type of quint) from rdb$database select cast (2000 as int) from rdb$database. If TYPE OF is used with a (VAR)CHAR type, its character.
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.
I understand that a char variable can accept a null character(1 byte) i.e; \0 as its value but, I don't understand how a char variable in my application below accepts a pointer(4 bytes)...
How can I run a MySQL query that selects everything that is not null? It would be something like … Do I just remove the all and go..?
Note: not a NULL field value, but the null character (see link). I have a column with a mix of typical and a null character.
Note: A NULL value is different from a zero value or a field that contains spaces.
> char array[SIZE] = {0}; Nothing wrong with this. It just assumes that the remaining SIZE-1 elements are also zero, so that's it, job done.
Предикат IS NULL позволяет проверить отсутствие (наличие) значения в полях таблицы. Использование в этих случаях обычных предикатов сравнения может привести к неверным результатам, так как сравнение со значением NULL дает результат UNKNOWN (неизвестно).