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# Type Mapping
Type mappings below apply to the **native TCP transport** (the default). See [WebSocket transport differences](#websocket-transport-differences) if you use `transport=websocket`.
## Exasol to Arrow Type Conversions
| Exasol Type | Arrow Type | Notes |
|----------------------------------|-------------------------------------|---------------------------------|
| `BOOLEAN` | `Boolean` | |
| `CHAR`, `VARCHAR` | `Utf8` | |
| `DECIMAL(p, s)` | `Decimal128(p, s)` | Precision 1–36 |
| `DOUBLE` | `Float64` | |
| `REAL` | `Float64` | |
| `INTEGER` | `Decimal128(18, 0)` | Alias of `DECIMAL(18, 0)` |
| `SMALLINT` | `Decimal128(9, 0)` | Alias of `DECIMAL(9, 0)` |
| `DATE` | `Date32` | |
| `TIMESTAMP` | `Timestamp(Microsecond, None)` | 0–9 fractional digits |
| `TIMESTAMP WITH LOCAL TIME ZONE` | `Timestamp(Microsecond, None)` | `Timestamp(Microsecond, "UTC")` over WebSocket |
| `INTERVAL YEAR TO MONTH` | `Interval(MonthDayNano)` | Months only |
| `INTERVAL DAY TO SECOND` | `Interval(MonthDayNano)` | Days and nanoseconds |
| `BINARY` | `Binary` | |
| `GEOMETRY` | `Binary` | Bytes of the WKT text |
| `HASHTYPE` | `Binary` | Bytes of the hash text |
## Precision and Scale
### DECIMAL
Exasol supports `DECIMAL(p, s)` where:
- **Precision (p):** 1 to 36 digits
- **Scale (s):** 0 to p
Arrow `Decimal128` preserves the exact precision and scale.
### TIMESTAMP
Exasol timestamps support 0–9 fractional digits. Arrow stores timestamps at microsecond precision, which covers most use cases.
### DATE and TIMESTAMP before 1970
`Date32` counts days and `Timestamp` counts microseconds from 1970-01-01 00:00:00. Values before that point are negative. Both use the proleptic Gregorian calendar and apply it to the year, month, and day that Exasol reports. This is the same calendar that Arrow tools use.
Exasol labels dates before 1582-10-15 in the Julian calendar. The driver converts the year, month, and day as Exasol shows them, so such a date has the same text in Arrow tools as in Exasol. This has three consequences:
- A day difference across 1582-10-15 is not the same as Exasol's `DAYS_BETWEEN`.
- February 29 of the years 100, 200, 300, 500, 600, 700, 900, 1000, 1100, 1300, 1400, and 1500 converts to March 1, because Arrow's calendar has no such day.
- On import, a `Date32` value for 1582-10-05 to 1582-10-14 becomes Exasol text that Exasol stores as 1582-10-15.
Import and parameter binding convert Arrow values to Exasol text with the same calendar. Values outside 0001-01-01 to 9999-12-31 are rejected.
### Parameter binding of dates and timestamps
An Arrow Timestamp of any unit binds as its UTC date and time at microsecond precision, with nanoseconds rounded down. Date32 binds as DATE. On the native transport, text bound to a DATE or TIMESTAMP parameter must use the form `YYYY-MM-DD` or `YYYY-MM-DD HH:MI:SS.FFFFFFFFF`, with the time part optional. Other text, such as ISO 8601 with a `T` separator, fails before execution. On the WebSocket transport, the driver sends the text to Exasol, which casts it. Exasol may accept forms the native transport rejects, and it rejects invalid text at execution.
### INTERVAL
Both interval types are returned as `Interval(MonthDayNano)`, on the native and the WebSocket transport. Exasol sends the value as text, and the driver parses it:
- `INTERVAL YEAR TO MONTH`: the text `+01-02` becomes 14 months, 0 days, and 0 nanoseconds. The months are `years * 12 + months`.
- `INTERVAL DAY TO SECOND`: the text `-03 04:05:06.789` becomes 0 months, -3 days, and -14706789000000 nanoseconds. The days and the time of day fill the day and nanosecond members.
The sign of the text applies to every member. A YEAR TO MONTH value fills only the month member, and a DAY TO SECOND value fills only the day and nanosecond members.
Arrow stores the month count as a 32-bit signed integer, so the largest `INTERVAL YEAR TO MONTH` value is 178,956,970 years and 7 months (`+178956970-07`). A larger value, such as `INTERVAL YEAR(9) TO MONTH` `999999999-11`, fails the query with an error that names the column. The driver never returns a wrapped month count.
### GEOMETRY
Geometry values are returned as Arrow `Binary` columns. Each value holds the bytes of the **WKT (Well-Known Text)** that Exasol sends, not WKB. Decode the bytes as UTF-8 to get the text:
```
POINT (1 2)
LINESTRING (0 0, 1 1, 2 2)
POLYGON ((0 0, 4 0, 4 4, 0 4, 0 0))
```
### HASHTYPE
Hash values (MD5, SHA-1, SHA-256, UUID, etc.) are returned as Arrow `Binary` columns. Each value holds the bytes of the text that Exasol sends, which follows the session setting `HASHTYPE_FORMAT`. With the default `HEX`, the value is the hexadecimal text, such as the 32 bytes of `550e8400e29b11d4a716446655440000`. With `UUID` or `BASE64`, it is the text in that format. The bytes are not the decoded hash.
## NULL Handling
All types support NULL values. Arrow represents nulls via validity bitmaps, which is compatible with Exasol's NULL semantics.
## Field Metadata
Every field of a result set carries the Exasol type of its column as Arrow field metadata. This applies to `ResultSet::metadata().schema`, to the schema of every RecordBatch, to a zero-row result, and to the schema that ADBC returns, on the native and the WebSocket transport. Arrow data types and values do not change.
| Key | Carried by | Example value |
|-----|------------|---------------|
| `exasol:type_name` | every column | `DECIMAL`, `TIMESTAMP WITH LOCAL TIME ZONE` |
| `exasol:type` | every column | `{"type":"DECIMAL","precision":10,"scale":2}` |
| `exasol:precision` | `DECIMAL` | `10` |
| `exasol:scale` | `DECIMAL` | `2` |
| `exasol:size` | `CHAR`, `VARCHAR` | `50` |
| `exasol:srid` | `GEOMETRY` on the WebSocket transport | `4326` |
`exasol:type_name` is the Exasol type name without parameters, which follows the JDBC `getColumnTypeName` convention. `exasol:type` holds the serialized `ExasolType`. To restore the `ExasolType` of a field, pass its metadata to `TypeMapper::from_field_metadata`:
```rust
let exasol_type = TypeMapper::from_field_metadata(field.metadata());
```
Every result set field is nullable, even when the column is declared `NOT NULL`, because Exasol reports no column nullability on either protocol.
Some metadata values do not reflect the declared column type:
- On the native transport, `GEOMETRY` carries no SRID, because the protocol sends none, so the key `exasol:srid` is absent. On the WebSocket transport, the key holds the SRID that Exasol reports, which is `0` for a column declared without one.
- On the native transport, `TIMESTAMP WITH LOCAL TIME ZONE` reports `TIMESTAMP`, because the protocol sends the same wire type for both.
- For `HASHTYPE`, `exasol:type` holds the byte size as half the size that Exasol reports, because Exasol reports the number of hex characters, which assumes the default session format `HASHTYPE_FORMAT=HEX`. With `UUID` or `BASE64`, Exasol reports another size, and the byte size is wrong. Without a reported size, the byte size is 16.
## WebSocket Transport Differences
When using `transport=websocket`, the following types map differently from the native protocol:
| Exasol Type | Native (default) | WebSocket |
|----------------------------------|--------------------------------|---------------------------------|
| `TIMESTAMP WITH LOCAL TIME ZONE` | `Timestamp(Microsecond, None)` | `Timestamp(Microsecond, "UTC")` |