In your table dump, you show the author field as containing string values:
Yet in your query, you are treating the field as containing a *NUMBER*:
AND author = $clientID
Which is it? If you really have a string value ("me", "you") then clearly you are never going to get a match on $clientID, which is just as clearly a number (since you don't have '...' around the value and it doesn't cause a syntax error, apparently).
EDIT: Yea, what Felgall asked. Only I'm more long-winded. <grin/>
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A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.