SQL: Creating Databases and Tables - Alter Table

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SQL: Creating Databases and Tables - ALTER TABLE

ALTER TABLE

The ALTER TABLE statement changes an existing table’s structure.

Action Statements:

• Add column

• Drop Column

• Rename Column

• Add Constraint

• Rename to

Syntax:

-- ALTER TABLE
ALTER TABLE table_name action;

Example: Alter Table

-- DROP Table
DROP TABLE IF EXISTS link;

## data frame with 0 columns and 0 rows

-- CREATE LINK
CREATE TABLE link(
link_id serial PRIMARY KEY,
title VARCHAR (512) NOT NULL,
url VARCHAR(1024) NOT NULL UNIQUE
);

## NULL

-- Select
SELECT * FROM link;

## NULL

-- ALTER
ALTER TABLE link ADD COLUMN active boolean;

## NULL

-- Select
SELECT * FROM link;

## NULL

Example: Rename link to url_table

-- ALTER Table to url_table
ALTER TABLE link RENAME TO url_table;

## NULL

-- SELECT
SELECT * FROM url_table;

## data frame with 0 columns and 0 rows