SQL Server – SQL Table Basics – Altering/Adding Columns
Adding column
You can add new columns to an existing table. .
ALTER TABLE [dbo].[phone] ADD inactive_date DATETIME NULL GO
Alter column
You can add modify an existing column
ALTER TABLE [dbo].[person]
ALTER COLUMN [lastname] VARCHAR(35) NULL
GO
Considerations for altering a column
- Reducing precision (example, going from CHAR(20) to CHAR(15)) can cause data truncation and should be avoided unless you are absolutely sure their will be no impact to the data.
- Changing data types should typically be avoided. There are exceptions to this. For example, changing a CHAR(20) to a VARCHAR(20) on columns where the average storage length is 10 can save disk space.
Alter columns – No Can Do
- You cannot directly alter a a column that is part of the primary key
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