Module types

Traits dealing with DuckDB data types.

DuckDB uses a dynamic type system. Implementations of the ToSql and FromSql traits are provided for the basic types that DuckDB provides methods for:

• Strings (String and &str)
• Blobs (Vec<u8> and &[u8])
• Numbers

The number situation is a little complicated due to the fact that all numbers in DuckDB are stored as INTEGER (i64) or REAL (f64).

ToSql and FromSql are implemented for all primitive number types. FromSql has different behaviour depending on the SQL and Rust types, and the value.

• INTEGER to integer: returns an Error::IntegralValueOutOfRange error if the value does not fit in the Rust type.
• REAL to integer: always returns an Error::InvalidColumnType error.
• INTEGER to float: casts using as operator. Never fails.
• REAL to float: casts using as operator. Never fails.

ToSql always succeeds except when storing a u64 or usize value that cannot fit in an INTEGER (i64). Also note that DuckDB ignores column types, so if you store an i64 in a column with type REAL it will be stored as an INTEGER, not a REAL.

If the time feature is enabled, implementations are provided for time::OffsetDateTime that use the RFC 3339 date/time format, "%Y-%m-%dT%H:%M:%S.%fZ", to store time values as strings. These values can be parsed by SQLite’s builtin datetime functions. If you want different storage for datetimes, you can use a newtype. ToSql and FromSql are also implemented for Option<T> where T implements ToSql or FromSql for the cases where you want to know if a value was NULL (which gets translated to None).

Structs

• Null
  Empty struct that can be used to fill in a query parameter as NULL.

Enums

• FromSqlError
  Enum listing possible errors from FromSql trait.
• TimeUnit
  An absolute length of time in seconds, milliseconds, microseconds or nanoseconds. Copy from arrow::datatypes::TimeUnit
• ToSqlOutput
  ToSqlOutput represents the possible output types for implementers of the ToSql trait.
• Type
  DuckDB data types. See Fundamental Datatypes.
• Value
  Owning dynamic type value. Value’s type is typically dictated by DuckDB (not by the caller).
• ValueRef
  A non-owning static type value. Typically the memory backing this value is owned by SQLite.

Traits

• FromSql
  A trait for types that can be created from a DuckDB value.
• ToSql
  A trait for types that can be converted into DuckDB values. Returns [Error::ToSqlConversionFailure] if the conversion fails.

Type Aliases

• FromSqlResult
  Result type for implementors of the FromSql trait.