Comments on: SQL SERVER – Primary Key Constraints and Unique Key Constraints

By: Sourish Biswas

Sourish Biswas — Thu, 09 Feb 2012 13:55:49 +0000

I have checked
Primay Key does not allow NULL value

By: karthik

karthik — Fri, 27 Jan 2012 06:57:29 +0000

hai i need the command of without using constraint to drop the primary key

By: RK

RK — Mon, 02 Jan 2012 12:54:49 +0000

can you pls give real time examples of a just pk and a unique key which is not PK

By: Omkar Joshi

Omkar Joshi — Wed, 09 Nov 2011 09:08:20 +0000

i have two tables unit and item primary key(uid) of unit table is foreign key of item table
now i want to add the data in item table but due to foreign key problem my data is not inserted into item table in SQL server 2005

what is an alternate way to make insert query on database

By: Ashutosh

Ashutosh — Thu, 13 Oct 2011 14:59:58 +0000

perfect answer of unique value in Unique constraint

By: Hiren,

Hiren, — Sat, 01 Oct 2011 09:53:12 +0000

Hello Mr. Dave,
I read your articles so many time which are very fruitful for me,
From their I will get all most all the solutions of my query very easily , But I have some ambiguities
In my table. Lets give me solution for that .
My query is , may table is tab1(colname, tabname) here both are column name and multivalued
My table data is given as follows :
Opdate compupdtdtl
Cldate compupdtdtl
Totalamt loanstatus
[long list truncated]

My expected output is :
colname tab1 tab3 tab4
cldate cr_cp compupdtdlt rpl_emp_leave
loanid loantrans compupdtdtl loanstatus

Could you gime me solution of this problem ,
Anyone ?

By: Nilesh

Nilesh — Fri, 30 Sep 2011 07:17:35 +0000

Hi,
I have one question: I have one table Logs table lots of thread make entry in this table. The Primary key of this table in not identity column. I am getting primary key conflict error..what should i do now?

By: prabu

prabu — Thu, 29 Sep 2011 07:16:49 +0000

Really nice site…

By: madhivanan

madhivanan — Fri, 02 Sep 2011 08:05:00 +0000

Find the constraint name and use

alter table person drop constraint constraint_name

By: sarath

sarath — Thu, 01 Sep 2011 12:34:15 +0000

hello friends,help me on this

Create table person(p_id varchar(10) unique,
name_s varchar(20))

I have created a table person and set p_id as unique.
Now i want to delete the Unique for the P_id..
how can i do that in sql server… reply me asap

By: SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 6 of 31 Journey to SQLAuthority

Wed, 06 Jul 2011 01:31:51 +0000

[...] Both primary key and unique key enforce uniqueness of the column on which they are defined. But by default, the primary key creates a clustered index on the column, whereas unique key creates a non-clustered index by default. Another major difference is that primary key doesn’t allow NULLs, but unique key allows one NULL only. (Read more here) [...]

By: Neyaz khan

Neyaz khan — Tue, 10 May 2011 08:04:45 +0000

Yes u are Write Unique Constraint can Contain 1 null Value Because 1st Time Null Is Also Unique.

By: madhivanan

madhivanan — Mon, 02 May 2011 10:43:04 +0000

You need to post some sample data with expected result to help you

By: Rajendra Sorkhe

Rajendra Sorkhe — Thu, 28 Apr 2011 15:20:41 +0000

I want to update a table in which almost 20 records for a single name.
I want to update dates in a table which is assoicated with a single name for 20 records. I want to keep the name unchanged n want to update the dates as 3,4,5, and so on.

By: shivani

shivani — Wed, 27 Apr 2011 06:21:02 +0000

I am making project (desktop application) using C#.NET and SQL server 2008.I have used p.k and f.k in three tables….and when i update or delete or insert i get violation error and its natural but is there any solution that neither constraints get affected nor my prject.

By: Venkat

Venkat — Thu, 21 Apr 2011 22:02:01 +0000

SELECT A.* FROM A, B WHERE A.CITY = B.CITY AND (A.STATE B.STATE OR A.PINCODE B.PINCODE OR A.COUNTRY B.COUNTRY)

By: Prashanth

Prashanth — Sat, 09 Apr 2011 04:53:26 +0000

I have a two tables A1 & A2 with columns

ADD1, city, state, postal_code & country

& B_ADD1,B_state,B_postal_code & B_country.

The second table has the correct combination of city,state,postal_code and Country &

the first table can have errors.

I need to write a query or create a view which will fetch me all the combinations of A which does not have a perfect match in B

for example

A has
hyd,ap,500056,india
bombay,ap,500056,india

B has
hyd,ap,500056,india
bombay,mah,2993849,india

my query must return the error record from A

bombay,ap,500056,india

after checking all combinations in B

Thanks in Advance
Prashanth

By: Gaurav Mittal

Gaurav Mittal — Mon, 10 Jan 2011 11:53:35 +0000

first u have to make the not null
first u run the query
Alter table sample modify sno datatype not null

After this query u can define the primary key on the column.

By: Narasimha Y

Narasimha Y — Tue, 16 Nov 2010 16:21:29 +0000

Hi Ramya,

it seems the column PID is accepting null values..that’s why the PK constraint is not defined. go to the table design and remove the Allow Nulls check mark for the PID column and then try again.

By: Narasimha Y

Narasimha Y — Tue, 16 Nov 2010 15:58:25 +0000

Hi Swarup & ankhenatraj,

when i tried to create primary key as you said, i have also got the same error as you guys mentioned.

try the steps as deepika mentioned. here are the steps again for you.

1) right click on the table name and select “Modify” in the Object Explorer(which is right side of the query window)

2) remove the check mark for the column sno under Allow Nulls(which will then not allow the null values for that column and which is primary for creating the primary key)

3) close that window and it will ask to save that table, then save it

4) now again try to run the add constraint query, now it will execute successfully…

–Narasimha

By: madhivanan

madhivanan — Fri, 12 Nov 2010 14:48:20 +0000

You need to disable the constraint before alter and enable it after alter

By: harsha

harsha — Fri, 12 Nov 2010 11:57:23 +0000

Hi,
I have to alter some column’s datatype in many tables. Problem is, the columns are composite keys or foreign keys. When I am altering the data type its giving error

Server: Msg 5074, Level 16, State 8, Line 1
Server: Msg 4922, Level 16, State 1, Line 1

I do not want to drop the constraint as there are lots of data in the tables.
Please help

thanks
Harsha

By: madhivanan

madhivanan — Mon, 01 Nov 2010 08:17:41 +0000

Start with

select * from INFORMATION_SCHEMA.TABLE_CONSTRAINTS

By: heba talal

heba talal — Mon, 01 Nov 2010 07:56:02 +0000

hi,
i need a sql 2000 script to find the unique constraint in a spacific table

thnx

By: Brian Tkatch

Brian Tkatch — Tue, 25 May 2010 11:16:48 +0000

@ahmed

unique(a): COLUMN a must be UNIQUE by itself.
unique(b): COLUMN b must be UNIQUE by itself.
unique(a) unique(b): Both COLUMN a and b must be UNIQUE separately.
unique(a,b): COLUMNs a and B must be UNIQUE in combination.

a b
- -
1 2
1 3

That is unique(a,b), but is not unique(a) unique(b), because b is not UNIQUE on its own.