SQL ALTER TABLE Assertion

Introduction

ALTER command is without doubt one of the most vital SQL capabilities to know for database manipulation and administration. This Knowledge Definition Language (DDL) command can alter present tables by including, eradicating, or updating columns, constraints, and indexes. We’ll have a look at other ways to make use of the ALTER command to spotlight its flexibility. As well as, ALTER TABLE statements in SQL could also be used to vary the information kind of an present column to match new information wants.

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Overview

• Be taught the aim and performance of the SQL ALTER command.
• Perceive how and the place to make use of SQL’s ALTER TABLE statements.
• Discover numerous situations and examples demonstrating using this SQL perform.

Purposes of ALTER Command

The ALTER command in SQL can be utilized for a number of functions. Listed below are some frequent functions:

Pattern Desk

Right here’s a pattern desk on which we might be testing out numerous ALTER TABLE statements.

Including a New Column

So as to add a brand new column in our Worker desk, you should use the ADD COLUMN assertion.

ALTER TABLE staff
ADD COLUMN birth_date DATE;
SELECT emp_id, birth_date from Workers WHERE emp_id BETWEEN 1 AND 5;

This provides a brand new column named `birth_date` of kind DATE within the desk, however the values are empty as we simply added a brand new column in Workers.

Modifying an Present Column

To switch an present column, use the MODIFY or ALTER COLUMN clause.

ALTER TABLE staff
MODIFY COLUMN birth_date DATETIME;

The `birth_date` column within the `staff` desk adjustments from DATE to DATETIME kind. Equally we are able to change different information varieties as properly for different columns.

Dropping a Column

To take away an present column out of your desk, use the DROP COLUMN in SQL.

ALTER TABLE staff
DROP COLUMN birth_date;

This SQL question removes the birth_date column from the workers desk.

Including Constraints

The ALTER command’s makes use of lengthen to including constraints to a desk like including a major key, international key, or distinctive constraint.

ALTER TABLE staff
ADD CONSTRAINT pk_employee_id PRIMARY KEY (emp_id);

This may add a major key constraint named `pk_employee_id` on the `emp_id` column of the `staff` desk.

Eradicating Constraints

We use the DROP CONSTRAINT to take away a constraint from the desk.

ALTER TABLE staff
DROP CONSTRAINT pk_employee_id;

This may take away the first key constraint (pk_employee_id) from the Workers desk.

Renaming a Desk

The ALTER command may also rename a desk.

ALTER TABLE staff
RENAME TO workers;

This may rename the `staff` desk to `workers`.

Conclusion

DDL’s ALTER command could be very efficient for managing and altering database desk constructions. Customers can add, change, or delete columns and constraints, offering the flexibleness required for adaptable database design and administration. This command makes it straightforward to replace database constructions as wants change.

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