how to add primary key to existing table in sql code example

Example 1: add primary key to existing table sql

alter table Persion add primary key (persionId,Pname,PMID)

Example 2: change primary key sql

ALTER TABLE <Table_Name>
DROP CONSTRAINT <constraint_name>

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

Example 3: sql server add primary key to existing table with data

ALTER TABLE Production.TransactionHistoryArchive
   ADD CONSTRAINT PK_TransactionHistoryArchive_TransactionID PRIMARY KEY CLUSTERED (TransactionID);

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