How to Specify Default Values for Columns sql table in telugu 14

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SQL PRIMARY KEY Constraint

The PRIMARY KEY constraint uniquely identifies each record in a table.

Primary keys must contain UNIQUE values, and cannot contain NULL values.

A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).

SQL PRIMARY KEY on CREATE TABLE

The following SQL creates a PRIMARY KEY on the "ID" column when the "Persons" table is created:

MySQL:

CREATE TABLE Persons (

    ID int NOT NULL,

    LastName varchar(255) NOT NULL,

    FirstName varchar(255),

    Age int,

    PRIMARY KEY (ID)

);

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AUTO INCREMENT Field

Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table.

Often this is the primary key field that we would like to be created automatically every time a new record is inserted.

CREATE TABLE Persons (

    Personid int NOT NULL AUTO_INCREMENT,

    LastName varchar(255) NOT NULL,

    FirstName varchar(255),

    Age int,

    PRIMARY KEY (Personid)

);