Check out example codes for "how to make multiple keys as primary in bdms". It will help you in understanding the concepts better.

Code Example 1

CREATE TABLE `Donor`(
  `did` int(50) NOT NULL,
  `oid` int(50) NOT NULL,
  `dname` varchar(50) NOT NULL,
  `dblood` varchar(50) NOT NULL,
  PRIMARY KEY (`did`, `oid`)
);

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