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I have this case:
I am working on a screwed up application in which arraylist are using for implementing layer isolation.
i.e., It is using some function to convert each and every values it return from the SQLDataReader into an arraylist and then pass it to the UI Layer.
I want to know that whether this will help in anyway or will cause an overhead to the application(remember the appn. is screwed up!!)
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obymathew wrote:
I want to know that whether this will help in anyway or will cause an overhead to the application
This is the wrong way of decoupling layers:
1. This will add both complexity and overhead - you'll need a lot of casting on the UI layer, as ArrayLists store only objects.
2. Probably your data is being put on specific positions (e.g, al[1] is the customer name, al[2] your customer address, etc. This makes the application hard to debug, and change impact analysis very hard to do.
What I suggest:
If you still want or need to keep a strong isolation between these layers (e.g., the data or the UI layer can be used with other implementations) you can:
Create a 3rd assembly, which will define the interfaces that'll be used by both the data layer and the UI layer. From the data layer, return those interfaces, or arrays of those interfaces. To allow incremental changes, and to not disrupt everything when changing a method, provide a method on each interface that converts that data to an arraylist.
Before doing any changes, plan ahead a bit: make a backup (actually, you should use source control), create some basic unit tests and only then start working.
Don't forget that you may need to maintain two versions while you're converting things if your users need changes/bug corrections.
Yes, even I am blogging now!
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Hello again buddies,
I wonder how can I work with just time section of a datetime or smalldatetime object ignoring its date section. wouldn't it be better to provide a "time" data type?
What I am looking for is to query records that a datetime column of them is in a specified time with no importance on the date
---
"Art happens when you least expect it."
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Use DATEPART(). It is a bit of a mess if you want to do something like get me the records between 11:30 and 14:30 but it is doable.
Do you want to know more?
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Yes it works, thank you so much Colin 
I am sorry if my questions seems so amature, I guess I am a good programmer but a newbie in SQL which I feel is a great different programming environment. I promiss that will change!!!! 
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"Art happens when you least expect it."
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Den2Fly wrote:
a newbie in SQL .... I promiss that will change!!!!
We've all got to start somewhere.
Do you want to know more?
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Set them all to the same date.
CAST('1900-01-01T' + SUBSTRING(CONVERT(varchar, theTime, 126), 12, 12) AS datetime)
Grim (aka Toby) MCDBA, MCSD, MCP+SB
SELECT * FROM user WHERE clue IS NOT NULL
GO
(0 row(s) affected)
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Sorry, this is off topic, but:
"SELECT * FROM user WHERE clue IS NOT NULL
GO
(0 row(s) affected)" <--- 
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Seems a great trick, what about the performance? DATEPART or CAST??
---
"Art happens when you least expect it."
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As Colin indicated in his original response, usability and efficiency both depend greatly on exactly what you're doing with it.
Also, I've found that when you take two solutions to the same problem and compare them, it's possible that one solution is faster on one server, and the other is faster on a different one.
For instance, stripping the time from a datetime. There are many ways to do this, the two most common being CONVERT(varchar(8), theDate, 112) or DATEADD(day, 0, DATEDIFF(day, 0, theDate)). I find that DATEADD/DATEDIFF runs faster in our development environment by a factor of 5, but the CONVERT method is faster in our production environment by a factor of 2.
So, the short answer is that you should write the query both ways, and benchmark them on your own system to see which one is faster on your own server. It also depends greatly on where/how you're using it. If you're using it in the WHERE clause, either one of them is going to be a pig. If you're just using it in the SELECT clause, then it will probably depend on your system hardware and configuration.
Grim (aka Toby) MCDBA, MCSD, MCP+SB
SELECT * FROM user WHERE clue IS NOT NULL
GO
(0 row(s) affected)
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You are right. Thank you.
---
"Art happens when you least expect it."
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Hello is it possible in SQL (and specially SQL Server 2000) to perform a SELECT on result of another SELECT statement? something like this just as an example of what I am talking about:
SELECT * FROM (SELECT a.Name, a.EMail FROM Users a WHERE a.Gendre = 0) WHERE Name = 'Danielle'
Thanks for any note,
-Den
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"Art happens when you least expect it."
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SELECT myTable.* FROM (SELECT a.Name, a.EMail FROM Users a WHERE a.Gendre = 0) myTable WHERE Name = 'Danielle'
You need to provide an alias. Why do you want to do this ? It means the data needs to be processed twice.
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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HEllo Christian,
Thank you so much for your reply
The example I used was not my real requirement and as Colin said it could be easily relpaiced by an "AND". I have a rather complicated query in which I really need such an approach
Thank you again
---
"Art happens when you least expect it."
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Yeah, I guessed it was an example
I've sometimes felt I needed to do something similar, but I've always found a better performance alternative. In fact, we're ot allowed to write queries like this at work, and we write some complex queries Perhaps you could provide an example closer to what you're doing ?
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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Christian Graus wrote:
In fact, we're ot allowed to write queries like this at work
Do you mean as per the example? Or using a subquery in an inner join?
Either way, isn't it a bit restrictive. Surely a better approach would be to write the query which ever way makes most sense and then if it is too slow profile it to see where the bottle necks are and rewrite those sections.
Do you want to know more?
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Colin Angus Mackay wrote:
using a subquery in an inner join?
Bingo
Colin Angus Mackay wrote:
Either way, isn't it a bit restrictive.
The actual rule is, if you think you need to do it, ask and they'll show you why you don't
It works, I always find for myself why I don't.
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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hi
nice to see ur provided info anbout Select Subquries...
but u alos mentioned that u are not allowed to use such queries at work..then what u do ...where subquries are needed...and u don't have an alternate????
is there any more accurae and efficient way as an alternate to these sub-quries.
................................
munawar
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munawarhussain wrote:
then what u do ...where subquries are needed
They generally are not needed, that's the point.
munawarhussain wrote:
is there any more accurae and efficient way as an alternate to these sub-quries.
I usually find a way to use joins rather than subqueries. Obviously, if there physically is no other way, we'd use a subquery, but as a rule we're able to eliminate them.
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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Christian..thanks for reply..
may i know, in case, when u want to delete records is there any other way to delete data from more than one table with out using subquries??
in selecting data from multiple tables its possible to use joins..
okkkk
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You can use joins to delete as well. You can also use them to update.
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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As Christian said, why do you want to do this?
Surely it would be easier to write
SELECT Name, Email FROM Users WHERE Gendre = 0 AND Name='Danielle'
Of course it is a very useful thing if you want to perform inner joins on subqueries, but I found recently that the query optimiser can sometimes get itself in a bit of a fankle over that if the subquery operates on too much data: The Stored Procedure runs how fast?[^]
Do you want to know more?
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Hello Colin
Thanks for your note, you are right about that query but that was just an example. ( not a good one I think  ) and again you are right my real project is some INNER JOINs that I have found this a good way to achive the result
---
"Art happens when you least expect it."
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Yeah, joins are generally the answer rather than what you were doing before
Christian
I have several lifelong friends that are New Yorkers but I have always gravitated toward the weirdo's. - Richard Stringer
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Hello,
I want to call two stored procedures at the same time, so the results are stored in two tables in the same DataSet. Both stored procedures have one parameter with the same name and takes the same value.
I'm using C#. How would I do it?
Thanks,
-- LuisR
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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