Informatics Practices
What is the purpose of ALTER TABLE command ? Can you add new columns with constraints such as NOT NULL ? Give example to justify your answer.
SQL Queries
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Answer
The ALTER TABLE command is used to change definitions of existing tables. It is used to add columns, integrity constraints and redefine a column (datatype, size, default value) in a table.
Yes, we can add new columns with constraints such as NOT NULL, which ensures that a column must always contain a value (i.e., cannot be empty or null).
For example, to add a new column tel_number with the NOT NULL constraint in the Empl table, the statement is:
ALTER TABLE Empl
ADD COLUMN(tel_number integer NOT NULL);
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