Answers for "add a column in sql and change 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>)

sql change primary key to composite key

/* For SQL Server/Oracle/MS ACCESS */
    ALTER TABLE  AgentIdentification 
    DROP CONSTRAINT PK_Table1_Col1


    /* For MySql */
    ALTER TABLE  AgentIdentification 
    DROP PRIMARY KEY