NULL
Buy this Reference Manual in softcover from Barnes & Noble!
NULL
Значение NULL означает ``отсутствие данных''. Они является отличным от значения 0 для числовых типов данных или пустой строки для строковых типов (see section A.5.3 Проблемы со значением NULL).
При использовании форматов импорта или экспорта текстовых файлов (LOAD DATA INFILE, SELECT ... INTO OUTFILE) NULL можно представить как \N (see section 6.4.9 Синтаксис оператора LOAD DATA INFILE).
| Posted by Lars Aronsson on Friday January 17 2003, @9:19am | [Delete] [Edit] |
Note that in Oracle, and perhaps also in other traditional SQL databases, all columns have a type, length, and value (TLV), e.g. NUMBER(7) has the length of 7 digits, just like CHAR(7) has the length of 7 characters, and NULL is the zero length value of any type. This is why NULL is different from the number zero, which consists of one digit and thus has length one. This also means that in Oracle, the empty string is the same as NULL. If this is not the case in MySQL, it should be explained more clearly.
Add your own comment.