while ( <DATA> ) {
   if ( /^ALTER\s+TABLE\s+
         (\w+)                   # $1
         \s+ADD\s+CONSTRAINT\s+
         (\w+)                   # $2
         \s+PRIMARY\s+KEY\s+\(\s*
         (.+?)                   # $3
         \s*\)/x ) {

      print "\$1: <$1> \$2: <$2> \$3: <$3>\n";
   }
}
__DATA__
ALTER TABLE ORDERS ADD CONSTRAINT PK_ORDER_ORDER_NUM PRIMARY KEY ( ORDER_NUM)
ALTER TABLE ORDER_ITEMS ADD CONSTRAINT PK_ORDER_NUM_ITEMS PRIMARY KEY ( ORDER_NUM, ITEM_NUM, SUB_TYPE )