`octet_length` should accept binary types

[eddietejeda]

Is your feature request related to a problem or challenge?

octet_length only accepts string types. When we use a binary column, the plan fails:

Function 'octet_length' requires String, but received Binary (DataType: BinaryView)

A workaround for SUM(octet_length(col)) over binary is:

SUM(length(encode(col, 'hex')) / 2)

But this materializes 2x the column's bytes just to count it.

Describe the solution you'd like

Extend octet_length to natively accept Binary, LargeBinary, and BinaryView, returning the byte length.

• SQL:1999 defines OCTET_LENGTH for string values, including binary strings.
• PostgreSQL, DuckDB, Spark, MySQL, and SQLite accept binary values.
• utf8_to_int_type already maps Binary -> Int32, LargeBinary -> Int64, and BinaryView -> Int32.

We've implemented the solution internally and happy to submit PR.

datafusion/functions/src/string/octet_length.rs

Before:

impl OctetLengthFunc {
    pub fn new() -> Self {
        Self {
            signature: Signature::coercible(
                vec![
                    Coercion::new_exact(TypeSignatureClass::Native(logical_string()))
                        .with_encoding_preservation(EncodingPreservation::dictionary()),
                ],
                Volatility::Immutable,
            ),
        }
    }
}

After: the two-branch string|binary select that md5 uses:

impl OctetLengthFunc {
    pub fn new() -> Self {
        Self {
            signature: Signature::one_of(
                vec![
                    TypeSignature::Coercible(vec![
                        Coercion::new_exact(TypeSignatureClass::Native(logical_string()))
                            .with_encoding_preservation(
                                EncodingPreservation::dictionary(),
                            ),
                    ]),
                    TypeSignature::Coercible(vec![
                        Coercion::new_exact(TypeSignatureClass::Native(logical_binary()))
                            .with_encoding_preservation(
                                EncodingPreservation::dictionary(),
                            ),
                    ]),
                ],
                Volatility::Immutable,
            ),
        }
    }
}

Describe alternatives you've considered

 length(encode(col, 'hex')) / 2 // works but doubles the data to count it

Additional context

bit_length has the same gap and could be part in the same PR.