I have this queston that I cannot get a clear answer on. I have searched the internet to find out if using foreign keys have any performane benefits but some articles yes and some say no. So what should I believe here. Does foreign keys have any performance benefits.
View 4 RepliesHello again,
I'm going through my tables and rewriting them so that I can create relationship-based constraints and create foreign keys among my tables. I didn't have a problem with a few of the tables but I seem to have come across a slightly confusing hiccup.
Here's the query for my Classes table:
Code:
CREATE TABLE Classes
(
class_id
INT
IDENTITY
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
class_title
VARCHAR(50)
NOT NULL,
class_grade
SMALLINT
NOT NULL
DEFAULT 6,
class_tardies
SMALLINT
NOT NULL
DEFAULT 0,
class_absences
SMALLINT
NOT NULL
DEFAULT 0,
CONSTRAINT Teacher_instructs_ClassFKIndex1 FOREIGN KEY (teacher_id)
REFERENCES Users (user_id)
)
This statement runs without problems and I Create the relationship with my Users table just fine, having renamed it to teacher_id. I have a 1:n relationship between users and tables AND an n:m relationship because a user can be a student or a teacher, the difference is one field, user_type, which denotes what type of user a person is. In any case, the relationship that's 1:n from users to classes is that of the teacher instructing the class. The problem exists when I run my query for the intermediary table between the class and the gradebook:
Code:
CREATE TABLE Classes_have_Grades
(
class_id
INT
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
grade_id
INT
NOT NULL,
CONSTRAINT Grades_for_ClassesFKIndex1 FOREIGN KEY (grade_id)
REFERENCES Grades (grade_id),
CONSTRAINT Classes_have_gradesFKIndex2 FOREIGN KEY (class_id, teacher_id)
REFERENCES Classes (class_id, teacher_id)
)
Query Analyzer spits out: Quote: Originally Posted by Query Analyzer There are no primary or candidate keys in the referenced table 'Classes' that match the referencing column list in the foreign key 'Classes_have_gradesFKIndex2'. Now, I know in SQL Server 2000 you can only have one primary key. Does that mean I can have a multi-columned Primary key (which is in fact what I would like) or does that mean that just one field can be a primary key and that a table can have only the one primary key?
In addition, what is a "candidate" key? Will making the other fields "Candidate" keys solve my problem?
Thank you for your assistance.
what the best practice is for creating indexes on columns that are foreign keys to the primary keys of other tables. For example:
[Schools] [Students]
---------------- -----------------
| SchoolId PK|<-. | StudentId PK|
| SchoolName | '--| SchoolId |
---------------- | StudentName |
-----------------
The foreign key above is as:
ALTER TABLE [Students] WITH CHECK ADD CONSTRAINT [FK_Students_Schools]
FOREIGN KEY([SchoolId]) REFERENCES [Schools] ([SchoolId])
What kind of index would ensure best performance for INSERTs/UPDATEs, so that SQL Server can most efficiently check the FK constraints? Would it be simply:
CREATE INDEX IX_Students_SchlId ON Students (SchoolId)
Or
CREATE INDEX IX_Students_SchlId ON Students (SchoolId, StudentId)
In other words, what's best practice for adding an index which best supports a Foreign Key constraint?
Hello!I have a table A with fields id,startdate and other fields. id and startdateare in the primary key.In the table B I want to introduce a Foreign key to field id of table A.Is this possible? If yes, which kind of key I have to build in table A?Thx in advance,Fritz
View 6 Replies View RelatedHi,
We have a poorly performing SQL 2000 db. i have just defragged ( the HD, not indexes, these are done daily via SQL Agent) the data files of our server and have not found any improvement in response.
I have now got into using SQL profiler to analyse the server performance. in the results that the trace is returning there are some huge (REALLY BIG) values for the duration and cpu values but these rows have no textdata value returned (ie it is null)
why is this? for these rows, the reads and writes columns are also high.
if these rows are what is taking the cpu's time then how can i identify what the server is doing to make any changes?
any thoughts on what other values i might trace or what action i can take to find the slow down cause?
in performance manager the processors (dual Xeons) are rarely dropping below 60%.
thanks in advance
fatherjack
Dear Experts,
I'm a DBA, Working for a Product based company.
We are implementing our product for a certain client of huge OLTP.
our reports team is facing problem (error: all the reports are timed out).though the queries are written properly, Each query is taking some minutes of time.
I've given the command DBCC DROPCLEANBUFFERS.
the time immediately dropped to 10 sec.
now my question is :
please suggest me the DBCC commands or any DBA related commands to improve the performance of the application for my reports team.
Thanks in advance.
Vinod
Hi All,
from your experience in SQL 2005 - do i have any free software that can help in improve performance or can help in identifying performance bottleneck. two examples of performance and help that i use usually use are the maintenance plan that do (check DB > reorganized index > rebuild index > update statics) and the second software is the SQL 2005 DASHBOARD for the reporting help.
do you have any other free tools and help that you can give me for performance or any thing that i must have in my SQL 2005 servers.
Thx
I have a table called work_order which has over 1 million records and acontractor table which has over 3000 records.When i run this query ,it takes long time since its grouping bycontractor and doing multiple sub SELECTs.is there any way to improve performance of this query ??-------------------------------------------------SELECT ckey,cnam,t1.contractor_id,count(*) as tcnt,(SELECT count(*) FROM work_order t2 WHEREt1.contractor_id=t2.contractor_id and rrstm=1 and rcdt is NULL) as r1,(SELECT count(*) FROM work_order t3 WHEREt1.contractor_id=t3.contractor_id and rrstm=2 and rcdt is NULL) as r2,(SELECT count(*) FROM work_order t4 WHEREt1.contractor_id=t4.contractor_id and rrstm=3 and rcdt is NULL) as r3,SELECT count(*) FROM work_order t5 WHEREt1.contractor_id=t5.contractor_id and rrstm=4 and rcdt is NULL) as r4,(SELECT count(*) FROM work_order t6 WHEREt1.contractor_id=t6.contractor_id and rrstm=5 and rcdt is NULL) as r5,(SELECT count(*) FROM work_order t7 WHEREt1.contractor_id=t7.contractor_id and rrstm=6 and rcdt is NULL) as r6,SELECT count(*) FROM work_order t8 WHEREt1.contractor_id=t8.contractor_id and rcdt is NULL) as open_count,(SELECT count(*) FROM work_order t9 WHEREt1.contractor_id=t9.contractor_id and vendor_rec is not NULL) asAck_count,(SELECT count(*) FROM work_order t10 WHEREt1.contractor_id=t10.contractor_id and (rtyp is NULL or rtyp<>'R') andrcdt is NULL) as open_norwoFROM work_order t1,contractor WHEREt1.contractor_id=contractor.contractor_id andcontractor.tms_user_id is not NULL GROUP BYckey,cnam,t1.contractor_id ORDER BY cnam*** Sent via Developersdex http://www.developersdex.com ***Don't just participate in USENET...get rewarded for it!
View 2 Replies View RelatedHey guys,Here's my situation:I have a table called lets say 'Tree', as illustred bellow:Tree====TreeId (integer)(identity) not nullL1(integer)L2(integer)L3(integer)....L10(integer)The combination of the values of L1 thru L10 is called a "Path" , andL1 thru L10 values are stored in a second table lets say called'Leaf':Leaf====LeafId (integer)(identity) not nullLeatText varchar(2000)Here's my problem:I need to lookup for a given keyword in each path of the tree table,and return each individual column for the paths that match thecriteria. Here's the main idea of how I have this now.SELECT TreeId,L1,L2,...,L10, GetText(L1) + GetText(L2) as L2text + ...+ GetText(L10) AS PathTextINTO #tmp FROM Tree //GetText is a lookup function for the Leaf tableSELECT L1,GetText(L1),L2,GetText(L2),...,L10,GetText(L10) FROM #tmpWHERECharIndex(@keyword,a.pathtext) > 0Does anyone would know a better,smart, more efficient way toaccomplish this task? :)Thks,
View 1 Replies View RelatedSQL Experts,
I'm facing a performance issue with the following query...
The Output of the following Query is 184 Records and it takes 2 to 3 secs to execute the query.
SELECT DISTINCT Column1 FROM Table1 (NOLOCK) WHERE Column1 NOT IN
(SELECT T1.Column1 FROM Table1 T1(NOLOCK) JOIN Table2 T2 (NOLOCK)
ON T2.Column2 = T1.Column2 WHERE T2.Column3= <Value>)
Data Info.
No of records in Table1 --> 1377366
No. of distinct records of Column1 in Table1 --> 33240
Is there any way the above query can be rewritten to improve the performance, which should take less than 1 sec...
(I'm using DISTINCT because there are Duplicate records of Column1 inTable1 )
Any of your help in this regard will be greately appreciated.
--
ash
I am not an expert in either SSIS or VFP technology but know enough to get my way round. One anomaly I did discover I thought was worth sharing for all those concerned with getting large amounts of data out of VFP in as short a time as possible. When you search for performance tips in relation to SSIS the advice is to never use select table or view from data access mode list in ole db source as this effectively translates to select * from table and I've never come across anything to contradict this €“ well I am and let me explain why:
When you use SQL command as data access mode in ole db source (where ole db source is foxpro dbc) and you write out select column1, column 2 etc etc from table a etc etc and then connect that to a destination (in my case ole db destination) the SSIS task spends ages stuck on Pre-execute before anything happens (the bigger the fox tbl the longer the wait). What is happening behind scenes is that the foxpro engine (assuming its foxpro engine and not sql engine €“ either way don€™t think it matters too much) is executing the sql command and then writing results to a tmp (temp) file on your local temp folder €“ (in my case : C:Documents and SettingsautologinLocal SettingsTemp1). These files take up gigs of space and it is only when this process is complete does the SSIS task actually finish the Pre-execute and start the data transfer process. I couldn€™t understand a) why my packages were stuck on pre-execute for such long times? and b) why were the tmp files being created and why they were soo big?
If you change from SQL command in source to Table or view and then select your table from list the SSIS task when executed kicks off immediately and doesn€™t get stuck on pre-execute nor create any tmp files €“ so you save time and disk space. The difference in time is immense and if like me you were really frustrated with poor performance when extracting from VFP now you know why.
Btw maybe this does not apply to all versions of VFP but it certainly does to v7.
Hi,
I have database D1 which contains 5 million users and one more database D2 having 95k Users.
i wanted to insert common users into new database D3 based on filter which is Phone number and is unique value. Below is the structure of my tables in D1 and D2:
D1(database)
UserProfiles(Table)
UserId (Column Name)
UserProfiledata (Column Name)
D2 (database)
Alerts (Table)
PhoneNumbers (ColumnName - Unique)
Now userProfiles table contains data in string format as below:
User.state AA User.City CC User.Pin 1234 User.phonenumber 987654
so iam parsing for each user using cursor and writing phone numbers into some temp table and wanted to query D2 database to verify whether this phone number exists in Alerts Table of D2 database.
can anyone please suggest on how i can go ahead with this and also help me on how to improve perfomance.
Thanks,
-Veera
Hi everyone
I need a solution for this query. It is working fine for 2 tables but when there are 1000's of records in each table and query has more than 2 tables. The process never ends.
Here is the query
(select siqPid= 1007, t1.Gmt909Time as GmtTime,(t1.engValue+t2.engValue+t3.engValue+t4.engValue) as EngValue,
t1.Loc1Time as locTime,t1.msgId
into #temp5
from #temp1 as t1,#temp2 as t2,#temp3 as t3,#temp4 as t4
where t1.Loc1Time = t2.Loc1Time and t2.Loc1Time = t3.Loc1Time and t3.Loc1Time = t4.Loc1Time)
I was trying to do something with this query.
But the engValues cant be summed up. and if I add that in the query, the query isnt compiling.
(select siqPid= 1007, t1.Gmt909Time as GmtTime,
t1.Loc1Time as locTime,t1.msgId,(t1.engValue+t2.engValue+t3.engValue+t4.engValue) as engValue
--into #temp5
from #temp1 as t1
where exists
(Select 1
from #temp2 as t2
where t1.Loc1Time = t2.Loc1Time and
exists
(Select 1
from #temp3 as t3
where t2.Loc1Time = t3.Loc1Time and
exists
(Select 1
from #temp4 as t4
where t3.Loc1Time = t4.Loc1Time))))
I need immediate help on that, I would appreciate an input on it.
Thanks
-Sarah
I should add an Identity field (Identity=True) and a row version field(timestamp) to my table, and avoid to arrange tables into different databases, is it true in general?
View 4 Replies View RelatedI have a view which uses UNION of two tables. First table has a 1.5 Million records and the second one has 40,000 records. When I query the view with a column (that is indexed in both tables) in the where clause, it's taking taking 3 Minutes to give the result. The column is of DateTime data Type. Any ideas as to how to improve the query performance ???
TIA
-XLDB
Hello,
I have the following setup and I would appreciate any help in improving
the performance of the query.
BigTable:
Column1 (indexed)
Column2 (indexed)
Column3 (no index)
Column4 (no index)
select
[time] =
CASE
when BT.Column3 = 'value1' then DateAdd(...)
when BT.Column3 in ('value2', 'value3') then DateAdd(...)
END,
Duration =
CASE
when BT.Column3 = 'value1' then DateDiff(...)
when BT.Column3 in ('value2', 'value3') then DateDiff(ss,
BT.OrigTime, (select TOP 1 X.OrigTime from BigTable X where X.Column1 >
BT.Column1 and X.Column3 <> 'value4' order by X.Column1 ))
END,
FROM
BigTable BT where BT.Column3 = 'value1' OR (BT.Column3 in ('value2',
'value3') and BT.Column4 <> (select X.Column4 from BigTable X where
X.Column1 = BT.Column1 and X.Column3 = 'Value1'))
Apart from the above mentioned, there are a few more columns which are
just a part of select statement and are not in any condition statments.
The BigTable has around 1 Mil records and the response time is very
poor, it takes around 3 mins to retrieve the records (which would be
around 500K)
With the Statistics ON,
I get the following:
Table 'BigTable'. Scan count 2, logical reads 44184, physical reads 0,
read-ahead reads 0.
Table 'WorkTable'. Scan count 541221, logical reads 4873218, physical
reads 0, read-ahead reads 0.
Is there any way to increase the performance, so that I can get the
result under 1 minute?
Any help would be appreciated.
P.S: I tried indexing the Column3, but no improvement.
-SR
Hi all
I have a table that contains an ntext column for storing values up to a couple of Mb in size.
However, I estimate that 95% of the values stored in this ntext field will fit into an nvarchar(4000) field.
Is it worth me having both fields in the table?
i.e. For rows where the values < 4000 characters I would store the value in the nvarchar column. Otherwise I would use the ntext column.
Can anyone confirm whether this technique would increase performance given that ntext values are sort of stored separately to the rest of the table data?
A colleague of mine is an Oracle DBA and he mentioned this technique is fairly caommonly adopted in the Oracle world.
Thanks
Matt
i have column in table which contains tabs and " i want replace with space...i am using repalce function is thier other way to improve performance with out using replace function.
View 9 Replies View RelatedDear All,
i've tried with indexed views, but because the view is referenceing another view, i was unable to create a clustered index on that view.
so please let me know how can i improve the performance of the view.
thank you very much
Vinod
Even you learn 1%, Learn it with 100% confidence.
Hello,I have the following setup and I would appreciate any help in improvingthe performance of the query.BigTable:Column1 (indexed)Column2 (indexed)Column3 (no index)Column4 (no index)select[time] =CASEwhen BT.Column3 = 'value1' then DateAdd(...)when BT.Column3 in ('value2', 'value3') then DateAdd(...)END,Duration =CASEwhen BT.Column3 = 'value1' then DateDiff(...)when BT.Column3 in ('value2', 'value3') then DateDiff(ss,BT.OrigTime, (select TOP 1 X.OrigTime from BigTable X where X.Column1 >BT.Column1 and X.Column3 <> 'value4' order by X.Column1 ))END,FROMBigTable BT where BT.Column3 = 'value1' OR (BT.Column3 in ('value2','value3') and BT.Column4 <> (select X.Column4 from BigTable X whereX.Column1 = BT.Column1 and X.Column3 = 'Value1'))Apart from the above mentioned, there are a few more columns which arejust a part of select statement and are not in any condition statments.The BigTable has around 1 Mil records and the response time is verypoor, it takes around 3 mins to retrieve the records (which would bearound 500K)With the Statistics ON,I get the following:Table 'BigTable'. Scan count 2, logical reads 44184, physical reads 0,read-ahead reads 0.Table 'WorkTable'. Scan count 541221, logical reads 4873218, physicalreads 0, read-ahead reads 0.Is there any way to increase the performance, so that I can get theresult under 1 minute?Any help would be appreciated.P.S: I tried indexing the Column3, but no improvement.
View 1 Replies View RelatedI am developing reporting service and using lots of 'LEFT OUTER JOIN',I am worried about the performance and want to use some subquery toimprovethe performance.Could I do that like below,[the origin source]SELECT *FROM TableALEFT OUTER JOIN TableBON TableA.item1 = TableB.item1WHERE TableA.item2 = 'xxxx'TableB.item2 > yyyy AND TableB.item2 < zzzzI add the subquery to query every table before 'LEFT JOIN'--------------------------------------------------------------------------SELECT *FROM(SELECT *FROM TableAWHERE TableA.item2 = 'xxxx') TableCLEFT OUTER JOIN(SELECT *FROM TableBWHERE TableB.item2 > yyyy AND TableB.item2 < zzzz) TableDON TableC.item1 = TableD.item1WHERE TableC.item2 = 'xxxx'TableD.item2 > yyyy AND TableD.item2 < zzzz--------------------------------------------------------------------------Can anyone give me some suggestion?Thanks a lot.Leland Huang
View 2 Replies View RelatedHi All,I am getting slower performance of select statements in MS SQL. I amfinding select statements in MS SQL are even slower than MS ACCESS. Isthere any way to improve the performance of select statements in MSSQL by tuning the database of anything else??Thanks in advance!Hoque
View 3 Replies View RelatedDear Sql Server experts:First off, I am no sql server expert :)A few months ago I put a database into a production environment.Recently, It was brought to my attention that a particular query thatexecuted quite quickly in our dev environment was painfully slow inproduction. I analyzed the the plan on the production server (itlooked good), and then tried quite a few tips that I'd gleaned fromreading newsgroups. Nothing worked. Then on a whim I performed anUPDATE STATISTICS on a few of the tables that were being queried. Thequery immediately went from executing in 61 seconds to under 1 second.I checked to make sure that statistics were being "auto updated" andthey were.Why did I need to run UPDATE STATISTICS? Will I need to again?A little more background info:The database started empty, and has grown quite rapidly in the lastfew months. One particular table grows at a rate of about 300,000records per month. I get fast query times due to a few well placedindexes.A quick question:If I add an index, do statistics get automatically updated for thisnew index immediately?Thanks in advance for any help,Felix
View 17 Replies View RelatedHi,
We are thinking about buying new harddrives to improve sql server performance. Currently TEMPDB is running on a dedicated RAID 0 with 3 harddrives of 136 GB, 10.000 RPM. When running a large bulk insert within a SSIS package to 15 destination tables we notice high numbers in the Avg. and current Read Queue length (above 3000) of the drive where TEMPB is on. No other programs or swap file is using this RAID 0 drive. Can anyone tell me if it is worth buying 4 harddrives of 15.000 RPM each 33 GB big replacing the current 3 drives? How much impact will it have on the Avg. and Current Read queue length and will it improve the time sql server needs to bulk insert data?
Thanks.
Marc
Hi, I am using compact framework 1.1 and SQL CE database for my mobile application. My database has a total of 160000 rows of records and whenever i do a query searching, it will take about 20 seconds to look through the whole database if the record does not exist. Is there any method to improve the searching performance? i am using data reader for the query.
Thanks.
Can any body tell me how to know to what columns of other table it refers to.
shiva kumar
Could someone enlighten me as to the advantage of using the foreign key tab when in table design mode in the Enterprise Manager. Does it have any advantages ?? Is it necessary ??
thanks in advance
Paul
I haven't tried, but does anyone know if its possible to a have a foreign key for two tables when the tables reside in different databases (on the same server)?
Thanks,
Doug Smith
l'm trying to do inserts on tables with foreign keys and they keep crashing. Can somebody please help.Whats the best way of populating data that has foreign keys?
View 1 Replies View RelatedHow would I drop a foreign Key?
Thanks
Lystra
I need to know if this is required? I have products, with the help of their business account numbers, are naturally categorized numerically. I want to create a product category table and a product account table.
Example :
tbProductCategories
TypeCode | Description
1000 | Cups
2000 | Plates
tbProductAccounts
Account | Description
1001 | Mug
1002 | Glass
2001 | Plate
2002 | Saucer
With the above tables (which are made up :) ), would you include
a foreign key in tbProductAccounts indicating the type code?
What would the stored proc look like without it?
Create Procedure usp_GetProductAccounts
@iTypeCode int
AS
SELECT tbProductAccounts.Account,
tbProductAccounts.Description
FROM tbProductAccounts
WHERE tbProductAccounts.Account - iTypeCode > 0 AND < 999
Would this work? Or should the foriegn key always be included?
Mike B
I am creating a series of foreign keys in my new database, and so far everything is going fine. The company I work for never uses them, and I am working on my own stuff on my own time now.
I come across one table that I do want one field to allow zeroes, but when its set to a value, to exist in the other table.
To be more specific. I have a PO type table, which has an EmployeeID of the person who made the PO, and another field to store who received the PO when the order arrives. I want that 2nd Employee field to be zero until it's received.
I created an employee of zero, to allow the foreign key to be created. But all the other tables that have foreign keys to my Employee table I would prefer to not allow zeroes. So I changed them to use a check of (employeeid > 0).
Is it possible to have a foreign key say that I want the value from the Field in Table A to exist in table B, or to be zero? Or would it just be easier to leave off the foreign key in this one case?
Tks
Shiry writes "Hi, I'm a beginner and I'm a bit stuck here..
I'm creating this database for my homework, I'm using Marks & Spencer as an
example. It has a table, products, for the clothes
id
name
cat_id ....... connected to typ_cat
colour_id ...... connected to typ_colour
size_id ....... connected to typ_size
price
sup_id ....... connected to typ_sup ...... but here i'm stuck a bit, are you
allowed to connect a typ_table to another typ_table?
this is the typ_sup:
id
name
address
city_id ......... connected to typ_city
or rather have a separate sup table with the same id, name, address, city_id
id will be connected to typ_sup
and the products table.. sup_id will then be connected to typ_sup..?
What way is better? and is it allowed to connect a typ_table to another
typ_table?
Thanks in advance!!!!
Shiry"