making a combination of two columns unique.

How can I make a combination of 2 columns unique in mysql?

for example I want to have only one business in one town in my table.

 

You can use something like:

CREATE TABLE business (
businessname VARCHAR(100),
town VARCHAR(100),
.
.
.
.
PRIMARY KEY (businessname, town)
);

Code (markup):

 

Thanks Ajayr
Do you happen to know the alter code of it so I can change my current table.

 

Try this:

ALTER TABLE business
ADD PRIMARY KEY (businessname, town);

Code (markup):

If you have already defined a primary key for the table, then use this command first:

ALTER TABLE business
DROP PRIMARY KEY;

Code (markup):