Primary key

Change primary key sql

ALTER TABLE <Table_Name>
DROP CONSTRAINT <constraint_name>

ALTER TABLE <Table_Name>
ADD CONSTRAINT <constraint_name> PRIMARY KEY (<Column1>,<Column2>)

Source: stackoverflow.com

What is primary key

PRIMARY KEY  -- unique identifier for the entire row of record in a table 
             -- can not be null and must be unique

Primary key

CREATE TABLE Persons (
    Rollno int NOT NULL,
    FirstName varchar(255),
    LastName varchar(255),
    Age int,
    PRIMARY KEY (ID)
);

Source: computerscienceai.com

Primary key

Primary Key :
It is unique column in every table in a database
It can ONLY accept;
    - nonduplicate values
    - cannot be NULL

Primary key

CREATE TABLE purchase_orders (
    po_nr NUMBER,
    vendor_id NUMBER NOT NULL,
    po_status NUMBER(1,0) NOT NULL,
    created_at TIMESTAMP WITH TIME ZONE NOT NULL,
    CONSTRAINT pk_purchase_orders PRIMARY KEY(po_nr)
);

Source: datawitzz.com

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