ALTER

MySQL

Example

CREATE TABLE employees (
    ID INT PRIMARY KEY,
    Name VARCHAR(30),
    Age INT
);

ALTER TABLE employees
ADD COLUMN Position VARCHAR(30);

SELECT * FROM employees;

#End of Example Code

Output

+----+------+-----+----------+
| ID | Name | Age | Position |
+----+------+-----+----------+

#End of Output

Explanation

In the example provided, a new table called ‘employees’ is created with three columns: ‘ID’, ‘Name’ and ‘Age’. The ALTER TABLE statement is then used to add a new column ‘Position’ to the ‘employees’ table. The SELECT statement is used to view the contents of the updated ‘employees’ table.

PostgreSQL

Example

ALTER TABLE employee
ADD COLUMN email VARCHAR(50);

Output

No output is generated as ALTER TABLE runs silently without returning a report.

Explanation

In the provided example, the ALTER TABLE statement is used to modify the structure of the ‘employee’ table by adding a new column named ‘email’ of type VARCHAR with a maximum length of 50 characters.

SQL Server

Example

ALTER TABLE Employees
ADD Email varchar(255);

Output

Command(s) completed successfully.

Explanation

In the example provided, the ALTER TABLE statement is used to add a new column named Email of datatype varchar(255) to the Employees table. The varchar(255) specifies that the maximum length for the entries in the Email column is 255 characters. Execution of the code does not return an output table. Instead, a success message is returned, indicating the completion of the command.

Oracle

Example

ALTER TABLE employees
MODIFY (salary NUMBER(8, 2));

Output

The new definition of the salary column would be NUMBER(8,2). Since this is a DDL operation and doesn’t result any rows being returned, there is no actual output.

Explanation

The ALTER TABLE statement is used to add, delete/drop or modify columns in an existing table. In this example, the ALTER TABLE statement modifies the data type of the salary column of the employees table to NUMBER(8,2).

SQLite

Example

CREATE TABLE Employees (
    ID INTEGER PRIMARY KEY,
    name TEXT,
    age INTEGER
);

ALTER TABLE Employees
ADD COLUMN email TEXT;

Output

No output is returned for the ALTER TABLE statement in SQLite.

Explanation

In the example provided, a table named ‘Employees’ is created first with three columns: ‘ID’, ‘name’, and ‘age’. The ‘ALTER TABLE’ statement then adds a new column ‘email’ to the existing ‘Employees’ table. SQLite doesn’t return any output for this action.