prestodb/presto · error · NotSupportedException

ROW comparison not supported for fields with null elements

Error message

ROW comparison not supported for fields with null elements

What it means

RowType comparison/equality refuses to compare ROW values whose fields contain null elements: checkElementNotNull throws NotSupportedException("ROW comparison not supported for fields with null elements"). SQL semantics for comparing rows with nulls are undefined here, so the library fails explicitly rather than returning a possibly wrong result.

Source

Thrown at presto-common/src/main/java/com/facebook/presto/common/type/RowType.java:345

        return 0;
    }

    @Override
    public long hash(Block block, int position)
    {
        Block arrayBlock = block.getBlock(position);
        long result = 1;
        for (int i = 0; i < arrayBlock.getPositionCount(); i++) {
            Type elementType = fields.get(i).getType();
            result = 31 * result + TypeUtils.hashPosition(elementType, arrayBlock, i);
        }
        return result;
    }

    private static void checkElementNotNull(boolean isNull)
    {
        if (isNull) {
            throw new NotSupportedException("ROW comparison not supported for fields with null elements");
        }
    }
}

View on GitHub (pinned to 55bb57d202)

Solutions

Use COALESCE/null-safe semantics: IS NOT DISTINCT FROM or fill nulls with sentinel values before comparison.
Flatten the row and use IS DISTINCT FROM per field instead of comparing whole rows.
Rewrite the query so comparison keys exclude nullable components.

Example fix

// before
WHERE row_col = ROW(1, NULL)
// after
WHERE row_col IS NOT DISTINCT FROM CAST(ROW(1, NULL) AS ROW(int, int))

Defensive patterns

Strategy: validation

Validate before calling

if (row.isNull(i)) { /* resolve nulls before comparison */ }

Type guard

boolean isComparableRow(Block a, Block b) { for (int i = 0; i < a.getPositionCount(); i++) { if (a.isNull(i) || b.isNull(i)) return false; } return true; }

Try / catch

try { rowType.equalTo(left, right); } catch (NotSupportedException e) { /* treat as not-equal or use IS NOT DISTINCT FROM semantics */ }

Prevention

Use IS NOT DISTINCT FROM / null-safe comparisons on ROW columns.
COALESCE null fields to sentinels before struct comparisons.
Avoid nullable fields in join/group-by keys of type ROW.

When it happens

Trigger: Calling RowType.equalTo or RowType.compareTo on two rows where any corresponding element is NULL (isNull(i) true).

Common situations: GROUP BY / DISTINCT / equality checks on ROW columns with nullable members; ORDER BY on struct columns containing NULLs; joins on row-typed keys where fields can be null.

Related errors

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/f6423f9355160d1d. Report an issue: GitHub.