SQL ALTER Table

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What is alter table in SQL?

ALTER TABLE statement in SQL is used to add, delete, or modify columns in an existing table, but is also used to add and drop various constraints on an existing table

1. Syntax ALTER TABLE ADD column:

ALTER TABLE your_table_name
ADD your_column_name datatype;

2. Syntax ALTER TABLE DROP column:

ALTER TABLE your_table_name
ADD your_column_name datatype;

3. Syntax ALTER TABLE - ALTER/MODIFY column:

ALTER TABLE your_table_name
ALTER COLUMN your_column_name datatype;

ALTER TABLE your_table_name
MODIFY COLUMN your_column_name datatype;

Let's look at the "Users" table: We will have four columns as: "id", "first_name", "last_name" and "country".

ID	First Name	Last Name	Country
1	Clark	Kent	USA
2	Pire	Joveau	France
3	Nicky	Anderson	USA
4	Pepe	Martínez	Spain
5	Peter	Parker	SUA

SQL ALTER TABLE ADD column Example

Now using ALTER TABLE we want to add a column named "Date_Of_Birth" in the "Users" table.

Example

ALTER TABLE Users
ADD Date_Of_Birth date;

The table "Users" it will look like that:

ID	First Name	Last Name	Country
1	Clark	Kent	USA
2	Pire	Joveau	France
3	Nicky	Anderson	USA
4	Pepe	Martínez	Spain
5	Peter	Parker	SUA

Tags: SQL ALTER Table: and foreign key, add cokumn, add multiple columns, primary key, add constraint, delete column, change column name, add column with default, create index, rebame column, modify column
Can we alter table in SQL?
What is altering table in SQL?
How do I edit a table in SQL query?

Change Data Type Example

Now we want to change the data type of the column named "Date_Of_Birth" in the "Users" table.

Example

ALTER TABLE Users
ALTER COLUMN Date_Of_Birth year;

"Date_Of_Birth" column is now type year will be in a two or four digits format.

ALTER TABLE DROP COLUMN

The following SQL deletes the "Country" column from the "Users" table:

ALTER TABLE Users DROP COLUMN Country;

The result:

ID	First Name	Last Name
1	Clark	Kent
2	Pire	Joveau
3	Nicky	Anderson
4	Pepe	Martínez
5	Peter	Parker

SQL ALTER Table: and foreign key, add cokumn, add multiple columns, primary key, add constraint, delete column, change column name, add column with default, create index, rebame column, modify column
Can we alter table in SQL?
What is altering table in SQL?
How do I edit a table in SQL query?
SQL ALTER Table - sql tutorial

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