sql_time operator()(const sql_null_type &value) const { throw value_conversion_error(); }
sql_blob operator()(const sql_time &value) const { throw value_conversion_error(); }
sql_time::sql_time(const std::string &value) : value_(0), format_(TIMESTAMP) { if (!parse(value)) { throw value_conversion_error("unable to convert string to time"); } }