Copy Column Into Existing Table using SQL - sql

Question

I want to create a column in databaseA with the same name, type, length and precision as another column in databaseB.
I need something like this:
INSERT INTO dbo.databaseA(col_name)
SELECT col_name
FROM dbo.databaseB;
GO
But the *col_name* does not yet exist in databaseA. I want to create it with the same type as *col_name* in databaseB.
I've also looked at:
ALTER TABLE table_name ADD col_name data_type
INSERT INTO dbo.databaseA(col_name)
SELECT col_name
FROM dbo.databaseB;
GO
But I don't know the data_type of the column I need to copy.
Edit:
** I'm using SQL Server 2008 R2 **

Answer 1

You can retrieve the datatype of the column from the database by querying the system views, similar to the following:
SELECT c.*, s.name
FROM sys.columns c
INNER JOIN sys.objects o
ON c.object_id = o.object_id
INNER JOIN sys.types s
ON c.user_type_id = s.user_type_id
WHERE o.name = 'B'
AND c.name = 'ColumnName'
You'll need to connect to DatabaseB, replace o.name = 'B' with your table's name and replace c.Name = 'ColumnName' with your column's name.
Once you have the datatype you would need to construct a DDL statement to add the column to the table in database A, something along the lines of the following:
ALTER TABLE dbo.MyTableName ADD MyColumnName DATA_TYPE_HERE
Once the table has been updated you can construct and execute your insert statement:
INSERT INTO DatabaseA.dbo.MyTableName (column list)
SELECT (column list)
FROM DatabaseB.dbo.MyTableName
Note that the above assumes both databases are located on the same SQL Server Instance and they both reside in the dbo schema.
If this is something you plan on using in the future you should add some defensive programming steps to make sure you only add the column if the column doesn't already exist in the table.