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Suhi100
Starting Member
14 Posts |
 Posted - 2015-02-18 : 06:24:55
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Hello,
Can someone explain and possibly give and example on what
SELECT NULL means and how it works?
I often see this expression in views for example,e select NULL as field_name
Thanks |
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gbritton
Master Smack Fu Yak Hacker
2780 Posts |
Posted - 2015-02-18 : 09:54:10
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| SELECT NULL means return no value. SELECT NULL as field_name means return no value and call it field_name |
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Suhi100
Starting Member
14 Posts |
Posted - 2015-02-18 : 12:58:20
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Thanks Gerald,
and what is the practical use of it? Is it used to check if there are rows in a table or view?
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tkizer
Almighty SQL Goddess
38200 Posts |
Posted - 2015-02-18 : 13:10:14
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quote:
Originally posted by Suhi100
Thanks Gerald,
and what is the practical use of it? Is it used to check if there are rows in a table or view?
We'd need to see the code to be able to tell you why it is being done.
Tara Kizer
SQL Server MVP since 2007
http://weblogs.sqlteam.com/tarad/ |
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gbritton
Master Smack Fu Yak Hacker
2780 Posts |
Posted - 2015-02-18 : 13:10:57
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Say you want to populate a table with default data, you might write
insert into mytable (a, b, c)
select 1, NUll, 2
if you want to purposefully put no data in column b, perhaps for some particular test cases.
It's not hard to think up other uses as well. I often see it as a placeholder in a UNION:
select a,b,c from abc_data
union all
select d, e, null from de_data
since the union operator requires the same number (and types) of columns for all rowsets |
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Suhi100
Starting Member
14 Posts |
Posted - 2015-02-19 : 04:09:35
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It makes sense as I saw it in a UNION operator so as I understand it is because the number of columns have to match.
Thanks for the answers it is clear now |
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Select NULL