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How do you add a new column to a table?

SQLJunior~1 min read
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Adding a new column to an existing table is done with the ALTER TABLE command and the ADD COLUMN clause.

Syntax:

sql
ALTER TABLE Table_Name ADD COLUMN Column_Name Data_Type Constraints;

Example:

sql
ALTER TABLE Employees ADD COLUMN Salary DECIMAL(10,2);

Explanation:

  • ALTER TABLE Employees, picks the table we want to change.
  • ADD COLUMN Salary DECIMAL(10,2), adds a new Salary column, a number with two digits after the decimal point.

Notes

  • Several columns can be added in a single query (in some DBMSs).
  • Constraints can be added if needed: NOT NULL, DEFAULT value, and so on.

An example with a constraint:

sql
ALTER TABLE Employees ADD COLUMN HireDate DATE NOT NULL DEFAULT CURRENT_DATE;

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