Type System¶
Substrait tries to cover the most common types used in data manipulation. Types beyond this common core may be represented using simple extensions.
Substrait types fundamentally consist of four components:
| Component | Condition | Examples | Description |
|---|---|---|---|
| Class | Always | i8, string, STRUCT, extensions | Together with the parameter pack, describes the set of non-null values supported by the type. Subdivided into simple and compound type classes. |
| Nullability | Always | Either NULLABLE (? suffix) or REQUIRED (no suffix) | Describes whether values of this type can be null. Note that null is considered to be a special value of a nullable type, rather than the only value of a special null type. |
| Variation | Always | No suffix or explicitly [0] (system-preferred), or an extension | Allows different variations of the same type class to exist in a system at a time, usually distinguished by in-memory format. |
| Parameters | Compound types only | <10, 2> (for DECIMAL), <i32, string> (for STRUCT) | Some combination of zero or more data types or integers. The expected set of parameters and the significance of each parameter depends on the type class. |
Refer to Type Parsing for a description of the syntax used to describe types.
Note
Substrait employs a strict type system without any coercion rules. All changes in types must be made explicit via cast expressions.