How to add a column to a table in sql

How to add a column to an SQL table? Use the ALTER TABLE statement to specify the table name, column name, and data type; optionally set NOT NULL constraints and default values; run the ALTER TABLE statement to add a new column to the table.

How to add a column to a SQL table

Preface

In SQL, adding a column is a common operation that extends the table and adds additional information. This article will explain in detail how to use SQL statements to add a column to a table.

grammar

 <code class="sql">ALTER TABLE table_name ADD COLUMN column_name data_type [NOT NULL] [DEFAULT default_value];</code>

Parameter description

• table_name: The table name that needs to be added to the column.
• column_name: The name of the new column to be added.
• data_type: The data type of the new column.
• NOT NULL: Specifies whether a new column can contain null values. The default value is allowed null values.
• DEFAULT default_value: Specifies the default value for the new column. If not specified, the new column will contain a null value.

Operation steps

1. Open a database connection: Use the SQL client tool to connect to the database.
2. Use the ALTER TABLE statement: Use the above syntax to write an ALTER TABLE statement, specifying table names, column names, data types, and other optional parameters.
3. Execution statement: Run the ALTER TABLE statement to add the new column to the table.

Example

The following example adds a text column named "Email" to a table named "Customers" and sets the default value to "example@example.com":

 <code class="sql">ALTER TABLE Customers ADD COLUMN Email TEXT NOT NULL DEFAULT 'example@example.com';</code>

Notice:

• Make sure that the name of the new column is unique in the table.
• Select the appropriate data type to store the data in the new column.
• Consider whether to set NOT NULL constraints and default values ​​according to business needs.
• Before executing the ALTER TABLE statement, it is recommended to back up the database in case of unexpected situations.

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