private Convert FunctionConvert()
{
var expr = Expression();
Match(MySqlToken.KwUsing);
var tempStr = lexer.GetStringValue();
Match(MySqlToken.Identifier);
Match(MySqlToken.PuncRightParen);
var cvt = new Convert(expr, tempStr);
cvt.SetCacheEvalRst(cacheEvalRst);
return cvt;
}