The uMySQL driver supports various std:: types for both input and output directions and some userver-specific types.
The driver also supports aggregates of supported types as input or output parameters:
whenever there is a row-wise mapping to/from T, T is expected to be an SimpleAggregate, that is an aggregate type without base classes, const fields, references, or C arrays.

The following table shows how types are mapped from C++ to MySQL types.

C++ to MySQL Mapping

Input C++ types	Corresponding MySQLType
std::uint8_t/std::int8_t	TINYINT
std::uint16_t/std::int16_t	SMALLINT
std::uint32_t/std::int32_t	INT
std::uint64_t/std::int64_t	BIGINT
float	FLOAT
double	DOUBLE
std::string	TEXT
std::string_view	TEXT
const char *	TEXT
std::chrono::system_clock::timepoint	TIMESTAMP
storages::mysql::Date	DATE
storages::mysql::DateTime	DATETIME
formats::json::Value	TEXT
decimal64::Decimal<Prec, Policy>	DECIMAL

The driver also supports std::optional<T> for every supported type, and that maps to either NULL or exactly as T does, depending on whether is optional engaged or not.

Mapping MySQL types to C++ types is a more complicated matter:

First, the driver forbids mapping signed to unsigned or vice versa - an attempt to do so will abort in debug build and throw in release (this behavior is referred as UINVARIANT later), this check happens before actual extraction.
Second, the driver forbids mapping NULLABLE column into non-optional C++ type, an attempt to do so will UINVARIANT, this check happens before actual extraction. However, other combinations of optional/non-optional<->NULL/NOT NULL are supported:

Is column NULLABLE	Is type optional	behavior
true	true	allowed
true	false	UINVARIANT
false	true	allowed
false	false	allowed

Third, an attempt to parse DECIMAL will throw at extraction stage if precision/rounding policy of corresponding decimal::Decimal64<Prec, Policy> is violated.
Fourth, an attempt to parse DATE or DATETIME not within TIMEPOINT range into std::chrono::system_clock::timepoint will throw at extraction stage. The decision was made to allow this conversion, since it might be very convenient to use, but in general this conversion is narrowing.
Fifth, general type mismatch will UINVARIANT, however widening numeric conversions are allowed, this check happens before actual extraction. You can see to what C++ types MySQL types can map in the following table:

MySQL to C++ mapping

Output C++ type	Allowed MySQL types
std::uint8_t	TINYINT UNSIGNED NOT NULL
std::int8_t	TINYINT NOT NULL
std::optional<std::uint8_t>	TINYINT UNSIGNED NOT NULL, TINYINT UNSIGNED
std::optional<std::int8_t>	TINYINT NOT NULL, TINYINT
std::uint16_t/std::int16_t/optional	SMALLINT + all types above, with respect to signed/unsigned and NULL/NOT NULL
std::uint32_t/std::int32_t/optional	INT, INT24 + all types above, with respect to signed/unsigned and NULL/NOT NULL
std::uint64_t/std::int64_t/optional	BIGINT + all types above, with respect to signed/unsigned and NULL/NOT NULL
float	FLOAT NOT NULL
std::optional<float>	FLOAT NOT NULL, FLOAT
double	DOUBLE NOT NULL, FLOAT NOT NULL
std::optional<double>	DOUBLE, DOUBLE NOT NULL, FLOAT, FLOAT NOT NULL
std::string/optional	CHAR, BINARY, VARCHAR, VARBINARY, TINYBLOB, TINYTEXT, BLOB, TEXT, MEDIUMBLOB, MEDIUMTEXT, LONGBLOB, LONGTEXT, with respect to NULL/NOT NULL
std::chrono::system_clock::timepoint/optional	TIMEPOINT, DATETIME, DATE, with respect to NULL/NOT NULL
storages::mysql::Date + optional	DATE, with respect to NULL/NOT NULL
storages::mysql::DateTime +optional	DATETIME, with respect to NULL/NOT NULL
formats::json::Value + optional	JSON, with respect to NULL/NOT NULL
decimal64::Decimal<Prec, Policy> + optional	DECIMAL, with respect to NULL/NOT NULL

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