Update only in case where its not null [duplicate]

Question

I want update a column(a) from table1 with select from table2 but making update only when in table2 existing column(b) is not null. I dont want use where statement (is not null) cause it will influence all my code.

Example of my code:

update table1 set column(a) = (select column(b) from table2)

I'm trying something like this

update table1 set column(a) = not null(select column(b) from table2)

Example:

update ExpressMarketCheck set Barcode = (select barcode from ExpressMarket), Name=(select name from expressmarket), price=(select price from expressmarket)

What does "influence all my code" mean? Why can you nod use a simple, standard WHERE clause? — D Stanley
– D Stanley, Commented Sep 27, 2016 at 12:48

vignesh · Accepted Answer · 2016-09-27 12:46:13Z

1

You can use this query to achieve your constraint.

Update ExpressMarketCheck set Barcode = (select barcode from ExpressMarket where barcode IS NOT NULL)

answered Sep 27, 2016 at 12:46

vignesh

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4 Comments

jarlh Over a year ago

Uncorrelated sub-query?

Nebi Over a year ago

thats exactly what he doesn't want. " I dont want use where statement (is not null)"

vignesh Over a year ago

Thanks for the info guys. Initially that constraint wasn't there when I post the answer.

DiH Over a year ago

Its ok i will it works with little changes in my code! Thank you!

Muhammad Usman · Accepted Answer · 2016-09-27 12:50:37Z

1

mySQL has an IFNULL function, so you could do:

UPDATE your_table_name SET your_column_name= "data", scan_created_date = ISNULL( your_column_name, "data" ) WHERE id = X

edited Sep 27, 2016 at 12:50

answered Sep 27, 2016 at 12:48

Muhammad Usman

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2 Comments

Nebi Over a year ago

in SQL-Server you can use ISNULL()

Muhammad Usman Over a year ago

thanks for pointing to it -:)

Gordon Linoff · Accepted Answer · 2016-09-27 12:51:48Z

I think you want a join:

update emc set Barcode = em.barcode, Name = em.name, price= em.price from ExpressMarketCheck emc join expressmarket em on emc.?? = em.??;

I cannot tell from your question what columns should be used for the join. The ?? are placeholders.

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