risingwavelabs/risingwave · error

unexpected default value type for real

Error message

unexpected default value type for real

What it means

derive_default_value converts a MySQL floating-point default (ColumnDefault::Real) only into Float32, Float64, or Decimal. If the target column's RW DataType is anything else, the code bails with 'unexpected default value type for real'. This is a defensive check against mapping an f64 default into an incompatible column type.

Source

Thrown at src/connector/src/source/cdc/external/mysql.rs:242

    let datum = match default {
        ColumnDefault::Null => None,
        ColumnDefault::Int(val) => match data_type {
            DataType::Int16 => Some(ScalarImpl::Int16(val as _)),
            DataType::Int32 => Some(ScalarImpl::Int32(val as _)),
            DataType::Int64 => Some(ScalarImpl::Int64(val)),
            DataType::Varchar => {
                // should be the Enum type which is mapped to Varchar
                Some(ScalarImpl::from(val.to_string()))
            }
            _ => bail!("unexpected default value type for integer"),
        },
        ColumnDefault::Real(val) => match data_type {
            DataType::Float32 => Some(ScalarImpl::Float32(F32::from(val as f32))),
            DataType::Float64 => Some(ScalarImpl::Float64(val.into())),
            DataType::Decimal => Some(ScalarImpl::Decimal(
                Decimal::try_from(val).context("failed to convert default value to decimal")?,
            )),
            _ => bail!("unexpected default value type for real"),
        },
        ColumnDefault::String(mut val) => {
            // mysql timestamp is mapped to timestamptz, we use UTC timezone to
            // interpret its value
            if data_type == &DataType::Timestamptz {
                val = timestamp_val_to_timestamptz(val.as_str())?;
            }
            Some(ScalarImpl::from_text(val.as_str(), data_type).map_err(|e| anyhow!(e)).context(
                "failed to parse mysql default value expression, only constant is supported",
            )?)
        }
        ColumnDefault::CurrentTimestamp | ColumnDefault::CustomExpr(_) => {
            bail!("MySQL CURRENT_TIMESTAMP and custom expression default value not supported")
        }
    };
    Ok(datum)
}

View on GitHub (pinned to 6469eb736d)

Solutions

1. Align the MySQL column's DEFAULT with its type (numeric default only on numeric columns).
2. Change the column default in MySQL to a compatible constant (e.g. integer default for an integer column).
3. Adjust connector type mapping so the column maps to Float32/Float64/Decimal.

Example fix

// before (MySQL)
ALTER TABLE t MODIFY qty INT DEFAULT 1.5;
// after
ALTER TABLE t MODIFY qty INT DEFAULT 1;

SELECT COLUMN_NAME, COLUMN_TYPE, COLUMN_DEFAULT FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA='mydb' AND TABLE_NAME='t'
  AND COLUMN_DEFAULT IS NOT NULL
  AND COLUMN_DEFAULT LIKE '%.%'
  AND NOT (COLUMN_TYPE LIKE 'float%' OR COLUMN_TYPE LIKE 'double%' OR COLUMN_TYPE LIKE 'decimal%');

function realDefaultIsCompatible(mysqlColumnType, rwDataType) {
  return /^(float|double|decimal)/.test(mysqlColumnType) &&
    ["Float32","Float64","Decimal"].includes(rwDataType);
}

try { await createCdcTable('t'); } catch (e) { if (String(e).includes('unexpected default value type for real')) { /* make the MySQL default a constant of the column's own type */ } else throw e; }

When it happens

Trigger: A MySQL column with a real/floating default value (e.g. DEFAULT 1.5) whose mapped RW type is not Float32, Float64, or Decimal.

Common situations: Schema changes re-typing a float column to int/string while keeping the old default; type-mapping discrepancies between MySQL and RW (e.g. FLOAT mapped unexpectedly).

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• unexpected default value type for integer
• failed to deserialize MySQL value into rust value
• failed to deserialize MySQL value into rw value
• invalid value for boolean: {:?}
• failed to parse mysql default value expression, only constan

AI-assisted analysis of risingwavelabs/risingwave@6469eb736d (2026-09-11). Data as JSON: /api/errors/733ee1066afcf9e4. Report an issue: GitHub.