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What is the difference between type Undefined and Null?

Null for Requst
Undefined  -for any other

There is a huge difference between them! "Null" is a common type or value that represents the_absence_ of something.While the "undefined" is a value for representing of _existence_ of something but yet not defined, without a certain value.

While the "undefined" is a value for representing of _existence_ of something but yet not defined, without a certain value.

When i have to use Null and when Undefined?

to #5
It's common to happen NULL-values in queries with LEFT JOIN, when the system couldn't find the appropriate records in the right table.
And the value 'Undefined' is usually used in scripts (modules). For example, if you call a function and skip some parameters but use commas then the skipped parameters will be equal 'Undefined' inside the function. Look here:
>> f(1,,3)
>> the second parameter is 'undefined'.

And another sample to consider. Compare the results of "WHERE field = NULL" with "WHERE field = Undefined" when the field contents the NULL and Undefined. In other words, Undefined is equal Undefined because they are the same, but one NULL is not equal another NULL because.. hmm... because they are unknown, absent. But it's true only in queries. In scripts they are equal each other. It's a kind of magic :)

to (6)
so, i don't have to use NULL, but queries return it to me when "with LEFT JOIN, when the system couldn't find the appropriate records in the right table.", why it doesn't return undefined instead of NULL?

#7 undefined != NULL
undefined like a pointer to nowhere
NULL like a normally NULL

#6 Could You comment this:
http://screencast.com/t/T173ci6WvIxG

Doesn't it seem to be contradicting to your words, that "one NULL is not equal another NULL", ha?

to (7) Because NULL is common for this situation (similar to SQL)
And in some cases the system returns the Undefined to you even in queries, e.g. for empty fields of complex types.

#8
nothig != nothig
When i have to use nothing and when i have to use notjing?

#10
U whant to say me, that NULL is not common for 1C, but 1C need to use it?

to #12
NULL is common for SQL and 1C has a query language similar to SQL so it's no wonder that it has NULL too

#13
So, i need to use NULL, cause it comes from SQL and i have to use undefined, cause it comes from 1C, why i cant use NULL instead of udefined?

#14. You may. I have no objection.

#15
thx! I hope, i can do it!

#9
01.11.2011 14:56:35
In english please... you screen with russian words... i don`t undestand )

#17 this table translated as:
expression               |    value
NULL=NULL             |   true
NULL=Undefined       |   false
Undefined=Undefined |   true

:)

#18
It is true only in scripts, not in queries. Please fix it or admit your defeat. :)

NULL=NULL | It's false forever!

SQL: NULL = NULL | NULL
1C: NULL = NULL | True
Undefined = Undifened | True

SQL:
  NULL = NULL  | unknown
1С query:
  NULL = NULL  | false
  Undefined = Undifened | True
1С script:
  NULL = NULL  | true
  Undefined = Undifened | True