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SQL Tutorial

SQL Tutorial Introduction to SQL SQL syntax SQL SELECT SQL SELECT DISTINCT SQL WHERE SQL AND & OR SQL ORDER BY SQL INSERT INTO SQL UPDATE SQL DELETE

SQL Advanced Tutorial

SQL SELECT TOP SQL LIKE SQL wildcard SQL IN SQL BETWEEN SQL alias SQL connection (JOIN) SQL INNER JOIN SQL LEFT JOIN SQL RIGHT JOIN SQL FULL OUTER JOIN SQL UNION SQL SELECT INTO SQL INSERT INTO SELECT SQL CREATE DB SQL CREATE TABLE SQL constraints SQL NOT NULL SQL UNIQUE SQL PRIMARY KEY SQL FOREIGN KEY SQL CHECK SQL DEFAULT SQL CREATE INDEX SQL DROP SQL ALTER SQL AUTO INCREMENT SQL view SQL date SQL NULL value SQL NULL function SQL common data types SQLDB data type

SQL ALTER

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update time 2016-10-15

SQL AUTO INCREMENT

ALTER TABLE statement

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

SQL ALTER TABLE syntax

To add columns to the table, please use the following syntax:

ALTER TABLE table_name
ADD column_name datatype

To delete a column in a table, use the following syntax (please note that some database systems do not allow this method of deleting columns in a database table):

ALTER TABLE table_name
DROP COLUMN column_name

To change the data type of a column in a table, use the following syntax:

SQL Server/MS Access:

ALTER TABLE table_name
ALTER COLUMN column_name datatype

My SQL/Oracle:

ALTER TABLE table_name
MODIFY COLUMN column_name datatype

##SQL ALTER TABLE example

Please see the "Persons" table:

P_IdLastNameFirstNameAddressCity1HansenOlaTimoteivn 10Sandnes2SvendsonToveBorgvn 23Sandnes3PettersenKariStorgt 20Stavanger

Now, we want to add a column called "DateOfBirth" to the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons

ADD DateOfBirth date

Please note that the type of the new column "DateOfBirth" It is date, which can store the date. The data type specifies the type of data that can be stored in the column. To learn about the data types available in MS Access, MySQL and SQL Server, visit our complete

Data Types Reference.

Now, the "Persons" table will look like this:

P_IdLastNameFirstNameAddressCityDateOfBirth##1##2SvendsonToveBorgvn 23SandnesPettersen

Hansen

Ola

Timoteivn 10

Sandnes

##3

Kari

Storgt 20

Stavanger

Change Data Type Example

Now, we want to change the data type of the "DateOfBirth" column in the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
ALTER COLUMN DateOfBirth year

Please note that now the "DateOfBirth" column The type is year, which can store the year in 2-digit or 4-digit format.

DROP COLUMN Example

Next, we want to delete the "DateOfBirth" column in the "Person" table.

We use the following SQL statement:

ALTER TABLE Persons
DROP COLUMN DateOfBirth

Now, the "Persons" table will look like this :

P_Id	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger

submit

SQL AUTO INCREMENT

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