Yikes, didn't mean to start a huge discussion. Just to add more fuel to the fire, here's a guideline I found online:
The Chicago Manual of Style (sec. 14.15, p. 464) says:
Uncertainty often arises concerning the proper choice of the indefinite article before an acronym. A workable solution may be based on the way such an abbreviation is read. The assumption is that an acronym is read either as a series of letters or as a neologism, or coined word. Rarely is the acronym read as though all of the words were spelled out. If, as is usually the case, the acronym is treated as a series of letters, the choice of the article depends on the pronunciation of the first letter. (_an_ NAACP position vs. _a_ TVA power station)
If the acronym is widely pronounced as though it were a word, the article is determined by the pronunciation of the word. (_a_ LOOM meeting vs. _an_ LCD panel)
So, it you go by Ansi standards, AN SQL. If you go by US Gov't standards, A SQL.
'The rule is that ISO Standards spell out letters and pronounce names. US Government standards pronounce everything -- thus a PSRO (Phycians Standards Review Organization) is a "Piss Row"; I am not making that up.'
or did I say that backwards?