The term "clause" in the context of programming

Question

I've come across statements such as "the default clause" in the context of a switch statement or "the JOIN clause" in the context of SQL and I know what these statements mean but still I'd like to see a clear definition of the term.

Answer 1

It's pretty much the same as in English (or another language). A clause is an incomplete fragment of a sentence, or in this case a statement, that encapsulates an actor and an action. In your example of a join clause, the action is the join and the actor is the table being joined.

Answer 2

I think that there is a parallel between a sentence and a dependent clause in natural languages and between a statement and a clause in computer languages.

A clause does not stand by itself, but only makes sense within the context of a statement.

For example, the clauses

• "at 2:30" (adverbial clause)
• WHERE A.ID = B.ID (JOIN clause)

don't stand meaningfully on their own. However, those clauses make sense in the context of a sentence or statement.

• "Meet me at 2:30."
• SELECT A.NAME, B.ADDRESS FROM A, B WHERE A.ID = B.ID

A default clause in a switch statement of Java refers to the branch that is taken if none of the checked values match. The word "default" is somewhat problematic, as it usually means a failure of some sort (as in, "Your mortgage is in default"). With computer languages, it tends to mean "the unchosen choice."

It is a "clause" because it makes sense only in the context of other choices.