How to Add a Default-Value Column to an Existing SQL Server Table?

Enhancing SQL Server Tables: Adding Columns with Default Values

This guide demonstrates how to efficiently add a new column with a default value to an existing SQL Server table.

SQL Syntax:

<code class="language-sql">ALTER TABLE {table_name}
ADD {column_name} {data_type} {NULL | NOT NULL}
CONSTRAINT {constraint_name} DEFAULT {default_value}
WITH VALUES;</code>

Illustrative Example:

<code class="language-sql">ALTER TABLE MyTable
ADD NewColumn INT NULL
CONSTRAINT DF_MyTable_NewColumn DEFAULT 0
WITH VALUES;</code>

Key Considerations:

• Constraint Naming: While a constraint name ({constraint_name}) is optional, providing one improves readability and management. SQL Server will automatically generate a name if omitted.
• WITH VALUES Clause: This clause is crucial when adding a nullable column. It ensures the default value is applied to all existing rows in the table. For non-nullable columns, the default value is automatically populated.
• Data Insertion: When inserting new rows, omitting a value for the new column will result in the default value being used (for nullable columns). Explicitly setting the column to NULL will override the default value.

This approach streamlines the process of updating your SQL Server database schema. Remember to choose appropriate data types and consider the implications of nullable versus non-nullable columns.

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