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.
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'm querying the back-end of an application. For what ever reason the developer decided to use NVARCHAR for all fields. I'm having a problem with one of the "date" fields--somehow it got populated...
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..?
I have come across some code that says … What exactly is this doing? Is it getting the field names unitcost and markup? Why would you use "select null as..."? New to this sorry. Thanks.
Select null, 'Actual null' from dual union all select '', 'Null string' from dual union all select ' ', 'Single space' from dual union all
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.
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)...
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).