OracleDialect.scala

/**
 * :: DeveloperApi ::
 * Default Oracle dialect, mapping a nonspecific numeric type to a general decimal type.
 */
@DeveloperApi
case object OracleDialect extends JdbcDialect {
  override def canHandle(url: String): Boolean = 
url.startsWith("jdbc:oracle")
  override def getCatalystType(
      sqlType: Int, typeName: String, size: Int,
 md: MetadataBuilder): Option[DataType] = {
    // Handle NUMBER fields that have no precision/scale in special way
    // because JDBC ResultSetMetaData converts this to 0 precision and -127 scale
    // For more details, please see
    // https://github.com/apache/spark/pull/8780#issuecomment-145598968
    // and
    // https://github.com/apache/spark/pull/8780#issuecomment-144541760
    if (sqlType == Types.NUMERIC && size == 0) {
      // This is sub-optimal as we have to pick a precision/scale in advance whereas the data
      // in Oracle is allowed to have different precision/scale for each value.
      Some(DecimalType(38, 10))
    } else {
      None
    }
  }