This is the definition of Constitutional law that I used:
Constitutional law deals with the interpretation and implementation of the United States Constitution. As the Constitution is the foundation of the United States, Constitutional law deals with some of the fundamental relationships within our society, which includes relationships among the states, the states and the federal government, the three branches (The Executive, Legislature, Judiciary) of the federal government, and the rights (e.g., human rights and civil rights) of the individual in relation to both federal and state government.
Because the supreme court plays such an important role in interpreting the constitution, study of Constitutional Law focuses heavily on Supreme Court rulings. Some of the most familiar topics of Constitutional law are the due process clauses, freedoms of speech, freedom of the press, freedom of religion, and the Bill of Rights.
http://www.statelawyers.com/Practice/Practice_Detail.cfm/PracticeTypeID:22
“study of Constitutional Law focuses heavily on Supreme Court rulings.” is what I keyed on.
It would appear to be a specialized sub-set of the Common Law. Not everything in the common law involves the Constitution.