how to update column city value from 'A' to 'B' and 'B' to 'A' in single query

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how to update column city value from 'A' to 'B' and 'B' to 'A' in single query

dastagiri16

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September 25, 2013 at 1:21 am

#283627

hi,
I have a table like
id city
1 A
so i want to update city column from A to B and again B to A by in single statement..please help.
Thanks
Dastagiri

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Koen Verbeeck SSC Guru Points: 259105 More actions · Answer 1

UPDATE myTable

SET City = CASE WHEN City = A THEN B

WHEN City = B THEN A

END

Need an answer? No, you need a question
My blog at https://sqlkover.com.
MCSE Business Intelligence - Microsoft Data Platform MVP

dastagiri16 Hall of Fame Points: 3544 More actions · Answer 2

hi,

The below query only updating the city value from A to B not B to A

Please advice.

Thanks,

Dastagiri

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

Koen's query will work because SQL does updates in two phases, first where it reads the data second where it changes.

If it's not doing what you want, please post actual data and desired results (and the table's definition) so we can see what's happening.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

dastagiri16 Hall of Fame Points: 3544 More actions · Answer 4

hi,

one of the interviewer asked the question about updating...so i have added test table like below...

USE [Practice]

GO

/****** Object: Table [dbo].[mytable] Script Date: 09/25/2013 13:10:59 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

CREATE TABLE [dbo].[mytable](

[city] [nchar](10) NULL

) ON [PRIMARY]

GO

and i have inserted values like

insert into mytable (city) values ('A')

so now i want to write update querty to update city value from A to B then B to A by using any query....

Koen Verbeeck SSC Guru Points: 259105 More actions · Answer 5

Ah ok, so you want to update a value to a new value and then back to it's old value.

It seems rather pointless, are you sure that's what the interviewer meant?

Need an answer? No, you need a question
My blog at https://sqlkover.com.
MCSE Business Intelligence - Microsoft Data Platform MVP

dastagiri16 Hall of Fame Points: 3544 More actions · Answer 6

Koen,

Yes , i agree with you but i don't know its possible..i was not replied any thing when he raised that question becuase i thought that by using any recursive cte it will work.. So i searching for that..

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 7

So update it, then update it back?

Update MyTable

SET City = 'B'

WHERE City = 'A';

Update MyTable

SET City = 'A'

WHERE City = 'B';

You can't do it in one statement, because updating a column to one value and then updating it to another require two statements. Though you could just have a single statement that does nothing and it'll have the same effect.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

dastagiri16 Hall of Fame Points: 3544 More actions · Answer 8

dastagiri16

Hall of Fame

Points: 3544

September 25, 2013 at 1:59 am

#1652993

hi,

any single statement to complete this task

Koen Verbeeck SSC Guru Points: 259105 More actions · Answer 9

Sure.

SELECT 'Nothing' FROM myTable;

Et voila, the row still has the value A.

Need an answer? No, you need a question
My blog at https://sqlkover.com.
MCSE Business Intelligence - Microsoft Data Platform MVP

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 10

dastagiri16 (9/25/2013)
hi,
any single statement to complete this task

Um...

GilaMonster (9/25/2013)
You can't do it in one statement, because updating a column to one value and then updating it to another require two statements. Though you could just have a single statement that does nothing and it'll have the same effect.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 11

Koen Verbeeck (9/25/2013)
Sure.
SELECT 'Nothing' FROM myTable;
Et voila, the row still has the value A.

I can simplify that...

;

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Kenny Jozi SSCrazy Points: 2028 More actions · Answer 12

DECLARE @t TABLE(city VARCHAR(1))

INSERT INTO @t(city)

VALUES ('A'),( 'B'),( 'C'),( 'A'),( 'B'),( 'C'),( 'A');

-- do a select and not the results for comparison purposes

SELECT city FROM @t

UPDATE @t

SET city = CASE city

WHEN 'A' THEN 'B'

WHEN 'B' THEN 'A'

else city

END

-- select after update to compare with initial select

select * from @t

SQL 2000/2005/2008/2012 DBA - MCTS/MCITP

Dwain Camps SSC Guru Points: 86948 More actions · Answer 13

I'll get into the spirit of this thing you've got going here!

CREATE TABLE #MyTable

(

city nchar(10)

);

INSERT INTO #MyTable VALUES ('A');

WITH SampleData (city) AS

(

SELECT 'A' UNION ALL SELECT 'B' UNION ALL SELECT 'A'

)

UPDATE a

SET city = b.city

FROM #MyTable a

JOIN SampleData b ON 1=1;

SELECT * FROM #MyTable;

GO

DROP TABLE #MyTable;

😛

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My advice:
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dastagiri16 Hall of Fame Points: 3544 More actions · Answer 14

hi,

here i am not able to trust it is updated with 'A'

supose in cte last select statement can be changed to 'AA' it is not showing last updated record that is 'AA'

Thanks,

Dastagiri