How to add a new column in SQL

Add new columns to an existing table in SQL by using the ALTER TABLE statement. The specific steps include: determining the table name and column information, writing ALTER TABLE statements, and executing statements. For example, add an email column to the Customers table (VARCHAR(50)): ALTER TABLE Customers ADD email VARCHAR(50);

Adding a new column in SQL

In SQL, you can add new columns to an existing table by using the ALTER TABLE statement.

grammar:

 <code>ALTER TABLE table_name ADD column_name data_type [constraints];</code>

parameter:

• table_name : The name of the table to add column
• column_name : The name of the new column
• data_type : the data type of the new column, such as INT , VARCHAR , DATE , etc.
• constraints : optional column constraints, such as NOT NULL , DEFAULT , etc.

step:

1. Determine the table name and column information

Determines the table name, the name of the new column to which you want to add a column.

2. Write ALTER TABLE statements

Use the above syntax to write an ALTER TABLE statement. For example, to add a new column named email to the Customers table, the data type is VARCHAR(50) :

 <code>ALTER TABLE Customers ADD email VARCHAR(50);</code>

3. Execution statement

Execute the ALTER TABLE statement in the SQL editor or in the query window.

Example:

The following example shows how to add a new column named delivery_date in Orders table:

 <code>ALTER TABLE Orders ADD delivery_date DATE;</code>

After executing this statement, a new column named delivery_date is added to Orders table, with the data type DATE .

Notice:

• After adding a new column, the new column values ​​for all existing rows will be NULL unless DEFAULT constraint is specified.
• If you want to add a primary key column, you need to use the ADD PRIMARY KEY clause.
• If you want to add a foreign key column, you need to use the ADD FOREIGN KEY clause.

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