Database Discussion Boards

Re: to set foreign key or not to set?

Jassim Rahma13-Mar-14 10:30

Jassim Rahma

13-Mar-14 10:30

I did indexed it but do I still need (or is it better) to declare it as foreign key?

Technology News @ www.JassimRahma.com

Re: to set foreign key or not to set?

_AK_13-Mar-14 10:49

_AK_

13-Mar-14 10:49

As I mentioned creating a foreign key constraint is required for refrential integrety and normally is a good practice. It do have an impact on performance which can be reduced by creating an index. If you craete the index on foreign key it will reduce the lookups.

.AK.

Re: to set foreign key or not to set?

Jassim Rahma13-Mar-14 10:51

Jassim Rahma

13-Mar-14 10:51

so declaring it as foreign key is a good practice and will have an impact on the performance but after declaring it do you still recommend to index it or declaring is enough?

Technology News @ www.JassimRahma.com

Re: to set foreign key or not to set?

_AK_13-Mar-14 11:07

_AK_

13-Mar-14 11:07

Creating a foreign key is not mandatory but is advised to create. Here[^] is a link which tells about the importance of it.
Now here[^] is another article which tells about refrential integrity and performance degradation which might give you a bit more idea about this.

.AK.

Re: to set foreign key or not to set?

Jassim Rahma13-Mar-14 11:16

Jassim Rahma

13-Mar-14 11:16

Great

Thanks

Technology News @ www.JassimRahma.com

Re: to set foreign key or not to set?

_AK_13-Mar-14 11:21

_AK_

13-Mar-14 11:21

You are welcome.

.AK.

Group by (first letter)

nelsonpaixao12-Mar-14 16:42

nelsonpaixao

12-Mar-14 16:42

Hello,

in some table, how can i perform a group by not by the column string but only by the letter of that column

thanks Big Grin | :-D

nelsonpaixao@yahoo.com.br

trying to help & get help

Re: Group by (first letter)

Kornfeld Eliyahu Peter12-Mar-14 20:03

Kornfeld Eliyahu Peter

12-Mar-14 20:03

Yes.

SQL

GROUP BY SUBSTR([COLUMN], 1, 1)

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: Group by (first letter)

nelsonpaixao16-Mar-14 9:50

nelsonpaixao

16-Mar-14 9:50

thanks

nelsonpaixao@yahoo.com.br

trying to help & get help

sum of datediff to many dates

ahmad_yossef11-Mar-14 4:08

ahmad_yossef

11-Mar-14 4:08

i have this periods of experience i want to calculate the sum or total period of these periods

2004-01-06 2004-07-05
2004-07-07 2004-11-30
2010-07-01 2010-07-29
2011-06-12 2011-07-28
2012-07-22 2012-08-20
2013-10-17 2015-05-17

Lost & Forgotten

Re: sum of datediff to many dates

Tim Carmichael11-Mar-14 5:40

Tim Carmichael

11-Mar-14 5:40

If you provide the query you are trying to get working, you are more likely to get help.
What is the underlying database? SQLServer, Oracle, Postgres, etc?

Re: sum of datediff to many dates

ahmad_yossef11-Mar-14 23:05

ahmad_yossef

11-Mar-14 23:05

sql
i made a query calculate the datediff in days and sumed all days now i want to convert this days (integer) to years months and days
thanks

Lost & Forgotten

Re: sum of datediff to many dates

Tim Carmichael12-Mar-14 10:57

Tim Carmichael

12-Mar-14 10:57

ahmad_yossef wrote:
i want to convert this days (integer) to years months and days

Well, break it down.. if you have the number of days, how many days in a year? Let's assume 365; so number of years in int(number of days / 365).
Months... let's assume 30 days on average... Months = int((number of days - years * 365) / 30)
And days are then number of days - years * 365 - months * 30

If that doesn't work, better define what you're after.
Given the sample dates you provided, what are the values you calculated for years, months and days?

Re: sum of datediff to many dates

ahmad_yossef12-Mar-14 23:19

ahmad_yossef

12-Mar-14 23:19

thanks for your replay
but i face a problem when i have a number like 1456

the query will be like that

SELECT dayss, dayss / 365 AS years, (dayss - dayss / 365 * 365) / 30 AS Months, (dayss - dayss / 365 * 365) - (dayss - dayss / 365 * 365) / 30 * 30 AS days
FROM dbo.lv_npay_tmp3

which will return

days1 years months days
1456 3 12 1

and it should be

days1 years months days
1456 4 0 1

i hope you got me

thanks alot

Lost & Forgotten

Re: sum of datediff to many dates

Richard Deeming13-Mar-14 1:10

Richard Deeming

13-Mar-14 1:10

1456 == (3 × 365) + 361.

That's clearly not 4 years and 1 day.

The problem is that you're assuming 365 days per year, but only 30 days per month. (30 × 12) = 360, so you've lost five days.

You need to assume (365 / 12) = 30.4166666... days per month, which will give you an answer of 3 years, 11 months and 27 days.

SQL

SELECT
    dayss, 
    dayss / 365 As years, 
    Cast(Floor((dayss % 365) * 12 / 365.0) As int) As Months, 
    (dayss % 365) - Cast(Floor((dayss % 365) * 12 / 365.0) * 365.0 / 12 As int) As days
FROM
    dbo.lv_npay_tmp3

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Re: sum of datediff to many dates

Kornfeld Eliyahu Peter11-Mar-14 23:48

Kornfeld Eliyahu Peter

11-Mar-14 23:48

If the answer for your question isn't satisfying, than refine your question - do not post it again...

http://www.codeproject.com/Forums/1725/Database.aspx?select=4775204&tid=4775204[^]

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: sum of datediff to many dates

ahmad_yossef12-Mar-14 2:23

ahmad_yossef

12-Mar-14 2:23

i am sorry

Lost & Forgotten

Re: sum of datediff to many dates

Richard MacCutchan12-Mar-14 3:53

Richard MacCutchan

12-Mar-14 3:53

Click on your name and you can find all your previous messages.

Re: sum of datediff to many dates

jschell14-Mar-14 12:15

jschell

14-Mar-14 12:15

I will just say that this sort of exercise seldom ends well without business requirements.

I am not going to analyze all possible interpretations but I will provide and example from your own data.

2013-10-17 2015-05-17

A business person asks you for how many years in that. All of the following are possible answers.
- One. 2013-10 to 2014-10 is one year, but 2014-10 to 2015-05 isn't.
- Zero. Because 2013-10 to 2014-10 is one year but it isn't 2014-10 yet
- Three. 2013, 2014, 2015 = 3.
- Two. 2013-10 to 2014-10 is one year, but 2014-10 to 2015-05 is partial, so round up to get 2.
- Five. The dates are supposed to be based on the contract period not the annual service dates (which the above dates are.)
- 17. Because the person that actually wants this wants a count of months covered.

DSN

Lek Plepi11-Mar-14 1:27

Lek Plepi

11-Mar-14 1:27

Hello Guys
I have installed one software that works with local ms access database.
If you remove that database of course the software displays the warning that the database is missing.
Can i migrate this database to Sql server so the program will work with Sql and not with Ms Access anymore????

Re: DSN

cdpsource11-Mar-14 2:14

cdpsource

11-Mar-14 2:14

Yes you can migrate it to SQL DB manually to be in safe side but your software must be compatible with data-source.

Re: DSN

Mycroft Holmes11-Mar-14 2:25

Mycroft Holmes

11-Mar-14 2:25

Yes, there is (was) even migration tool to help you upsize to a proper database (SQL Server). You then only need to change your connection string to point to the SQL Server database.

Never underestimate the power of human stupidity
RAH

Ho to avoid Not In & In clause in my query

member002611-Mar-14 0:43

member0026

11-Mar-14 0:43

select id,name from stud where (id not in (select id from class)) and depid in (select depid from dep where rid=@rid)

Re: Ho to avoid Not In & In clause in my query

Bernhard Hiller11-Mar-14 1:04

Bernhard Hiller

11-Mar-14 1:04

What about:

SQL

Select DISTINCT id, name
FROM stud
INNER JOIN dep on stud.depid=dep.depid
LEFT JOIN class on stud.id=class.id
WHERE dep.rid=@rid 
AND stud.id is null

But I doubt that it's faster...

Re: Ho to avoid Not In & In clause in my query

member002611-Mar-14 18:08

member0026

11-Mar-14 18:08

Im not sure, but compare not in the join will be the faster one, i heared like that Frown | :(

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