Add new column with foreign key constraint in one command
SqlSql Problem Overview
I am trying to add a new column that will be a foreign key. I have been able to add the column and the foreign key constraint using two separate ALTER TABLE commands:
ALTER TABLE one
ADD two_id integer;
ALTER TABLE one
ADD FOREIGN KEY (two_id) REFERENCES two(id);
Is there a way to do this with one ALTER TABLE command instead of two? I could not come up with anything that works.
Sql Solutions
Solution 1 - Sql
As so often with SQL-related question, it depends on the DBMS. Some DBMS allow you to combine ALTER TABLE operations separated by commas. For example...
Informix syntax:
ALTER TABLE one
ADD two_id INTEGER,
ADD CONSTRAINT FOREIGN KEY(two_id) REFERENCES two(id);
The syntax for IBM DB2 LUW is similar, repeating the keyword ADD but (if I read the diagram correctly) not requiring a comma to separate the added items.
Microsoft SQL Server syntax:
ALTER TABLE one
ADD two_id INTEGER,
FOREIGN KEY(two_id) REFERENCES two(id);
Some others do not allow you to combine ALTER TABLE operations like that. Standard SQL only allows a single operation in the ALTER TABLE statement, so in Standard SQL, it has to be done in two steps.
Solution 2 - Sql
In MS-SQLServer:
ALTER TABLE one
ADD two_id integer CONSTRAINT fk FOREIGN KEY (two_id) REFERENCES two(id)
Solution 3 - Sql
For SQL Server it should be something like
ALTER TABLE one
ADD two_id integer constraint fk foreign key references two(id)
Solution 4 - Sql
In MS SQL SERVER:
With user defined foreign key name
ALTER TABLE tableName
ADD columnName dataType,
CONSTRAINT fkName FOREIGN KEY(fkColumnName)
REFERENCES pkTableName(pkTableColumnName);
Without user defined foreign key name
ALTER TABLE tableName
ADD columnName dataType,
FOREIGN KEY(fkColumnName) REFERENCES pkTableName(pkTableColumnName);
Solution 5 - Sql
In Oracle :
ALTER TABLE one ADD two_id INTEGER CONSTRAINT Fk_two_id REFERENCES two(id);
Solution 6 - Sql
2020 Update
It's pretty old question but people are still returning to it I see. In case the above answers did not help you, make sure that you are using same data type for the new column as the id of the other table.
In my case, I was using Laravel and I use "unsigned integer" for all of my ids as there is no point of having negative id LOL.
So for that, the raw SQL query will change like this:
ALTER TABLE `table_name`
ADD `column_name` INTEGER UNSIGNED,
ADD CONSTRAINT constrain_name FOREIGN KEY(column_name) REFERENCES foreign_table_name(id);
I hope it helps
Solution 7 - Sql
PostgreSQL DLL to add an FK column:
ALTER TABLE one
ADD two_id INTEGER REFERENCES two;
Solution 8 - Sql
For DB2, the syntax is:
ALTER TABLE one ADD two_id INTEGER FOREIGN KEY (two_id) REFERENCES two (id);
Solution 9 - Sql
ALTER TABLE TableName ADD NewColumnName INTEGER, FOREIGN KEY(NewColumnName) REFERENCES [ForeignKey_TableName](Foreign_Key_Column)
Solution 10 - Sql
You can do it like below in SQL Server
ALTER TABLE one
ADD two_id int foreign key
REFERENCES two(id)
Solution 11 - Sql
If you also need to add default values in case you already have some rows in the table then add DEFAULT val
ALTER TABLE one
ADD two_id int DEFAULT 123,
FOREIGN KEY(two_id) REFERENCES two(id);
Solution 12 - Sql
Try this:
ALTER TABLE product
ADD FOREIGN KEY (product_ID) REFERENCES product(product_ID);