MySQL type mapping

The tables below list every MySQL column type (MySQL 8.0 Data Types) and the Kotlin type produced when the column is read into a DataFrame. Aliases are canonicalised by MySQL at CREATE TABLE time, so DataFrame only ever sees the canonical type; they are listed in the same row as the canonical type for reference.

Column nullability is determined from the metadata provided by the JDBC driver. If the driver does not explicitly report a column as non-nullable, it is mapped to a nullable Kotlin type (Int? instead of Int).

Numeric types

Canonical	Aliases	DataFrame column type	Notes
`TINYINT[(M)]`	`INT1`	`Int`	1-byte signed integer (`-128 .. 127`).
`TINYINT UNSIGNED`	`INT1 UNSIGNED`	`Int`	1-byte unsigned integer (`0 .. 255`).
`BOOL`, `BOOLEAN`	(alias only)	`Boolean`	Stored as `TINYINT(1)`; values are `0`/`1`.
`SMALLINT[(M)]`	`INT2`	`Int`	2-byte signed integer.
`SMALLINT UNSIGNED`	`INT2 UNSIGNED`	`Int`	2-byte unsigned integer.
`MEDIUMINT[(M)]`	`INT3`, `MIDDLEINT`	`Int`	3-byte signed integer.
`MEDIUMINT UNSIGNED`	`INT3 UNSIGNED`, `MIDDLEINT UNSIGNED`	`Int`	3-byte unsigned integer.
`INT[(M)]`	`INTEGER`, `INT4`	`Int`	4-byte signed integer.
`INT UNSIGNED`	`INTEGER UNSIGNED`, `INT4 UNSIGNED`	`Long`	MySQL override: fits in `Long`, not `Int`.
`BIGINT[(M)]`	`INT8`	`Long`	8-byte signed integer.
`BIGINT UNSIGNED`	`INT8 UNSIGNED`	`java.math.BigInteger`	MySQL override: exceeds `Long`, needs `BigInteger`.
`DECIMAL(M,D)`	`DEC`, `NUMERIC`, `FIXED`	`java.math.BigDecimal`	Fixed-point.
`FLOAT[(P)]`	`FLOAT4`	`Float`	4-byte float. Becomes `Double` if the driver reports the column class as `java.lang.Double`.
`DOUBLE`	`FLOAT8`, `DOUBLE PRECISION`	`Double`	8-byte float.
`REAL`	(alias only)	`Double`	By default `REAL` is `DOUBLE`. Becomes `FLOAT` under the `REAL_AS_FLOAT` SQL mode.
`BIT(M)`	none	`ByteArray`	Reported as `BIT`/`VARBINARY`; `BIT(1)` may map to `Boolean`.

Date and time types

Canonical	Aliases	DataFrame column type	Notes
`DATE`	none	`java.util.Date`
`TIME[(fsp)]`	none	`java.sql.Time`	`fsp` is fractional seconds precision (0–6).
`DATETIME[(fsp)]`	none	`kotlin.time.Instant`	Preprocessed from `java.sql.Timestamp`.
`TIMESTAMP[(fsp)]`	none	`kotlin.time.Instant`	Preprocessed from `java.sql.Timestamp`.
`YEAR[(4)]`	none	`java.util.Date`	1-byte year (`1901..2155`); driver reports it as `Types.DATE`. Two-digit form `YEAR(2)` was removed in 5.7.5.

String types

Canonical	Aliases	DataFrame column type	Notes
`CHAR(M)`	`CHARACTER(M)`, `NATIONAL CHAR(M)`, `NCHAR(M)`	`String`	Fixed-length text. Max `M = 255`.
`VARCHAR(M)`	`CHARACTER VARYING(M)`, `NATIONAL VARCHAR(M)`, `NVARCHAR(M)`	`String`	Variable-length text.
`BINARY(M)`	none	`ByteArray`	Fixed-length binary.
`VARBINARY(M)`	`BINARY VARYING(M)`	`ByteArray`	Variable-length binary.
`TINYBLOB`	none	`ByteArray`	Up to 255 bytes.
`TINYTEXT`	none	`String`	Up to 255 bytes.
`BLOB[(M)]`	none	`ByteArray`	Up to 64 KiB.
`TEXT[(M)]`	none	`String`	Up to 64 KiB.
`MEDIUMBLOB`	`LONG VARBINARY`	`ByteArray`	Up to 16 MiB.
`MEDIUMTEXT`	`LONG VARCHAR`, `LONG`	`String`	Up to 16 MiB.
`LONGBLOB`	none	`ByteArray`	Up to 4 GiB.
`LONGTEXT`	none	`String`	Up to 4 GiB.
`ENUM(...)`	none	`String`	Enumeration; values read as their string form.
`SET(...)`	none	`String`	Comma-separated set of values, as a single string.

JSON

Canonical	Aliases	DataFrame column type	Notes
`JSON`	none	`String`	Validated JSON text. Physically distinct from `LONGTEXT` in MySQL; JDBC still returns it as text.

Spatial types

All spatial types are read as ByteArray (WKB / EWKB binary as reported by the driver).

Canonical	Aliases	DataFrame column type
`GEOMETRY`	none	`ByteArray`
`POINT`	none	`ByteArray`
`LINESTRING`	none	`ByteArray`
`POLYGON`	none	`ByteArray`
`MULTIPOINT`	none	`ByteArray`
`MULTILINESTRING`	none	`ByteArray`
`MULTIPOLYGON`	none	`ByteArray`
`GEOMETRYCOLLECTION`	none	`ByteArray`

MySQL specifics

INT UNSIGNED and BIGINT UNSIGNED are the only types that need MySQL-specific handling. INT UNSIGNED is widened to Long; BIGINT UNSIGNED becomes BigInteger because its range exceeds Long.
The value of REAL depends on the REAL_AS_FLOAT SQL mode: default REAL is DOUBLE; with REAL_AS_FLOAT set, it's FLOAT.
Display width (INT(11)) and ZEROFILL are server-side metadata and are not surfaced by MySQL Connector/J in getColumnTypeName(); DataFrame only ever sees the canonical name. Both attributes are deprecated for numeric types as of MySQL 8.0.17 — see Numeric Type Attributes.
TINYINT(1) is a special case: MySQL Connector/J reports it as Types.BIT (→ Boolean) by default because of the driver's tinyInt1isBit property. Set tinyInt1isBit=false in the JDBC URL to read it as Int instead.

Unsupported types

Spatial types have no native Kotlin representation — read as raw WKB ByteArray.
VECTOR (MySQL 9.0+); the driver reports it as a binary type, so DataFrame reads it as ByteArray.

09 September 2026