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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Flink introduced Descriptor API to configure and instatiate TableSources/TableSinks since 1.5.0, i.e. the TableEnvironment#connect API.

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/** creates a temporary table from a descriptor. */
void createTemporaryTable(String tablePath, TableDescriptorTableDe
scriptor tableDescriptor);

The TableDescriptor is an unified interface/class to represent a SQL DDL strucutre (or CatalogTable internally). It can be a specific connector descriptor, e.g. Kafka, or a general purpose descriptor, i.e. Connector. All the methods can be chained called on the instance, including .schema(), .partitionedBy(), and .like(). We will discuss TableDescriptor in detail in the Proposed Changes section.

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With the above two methods, we can leverage the same TableDescriptor definition, then Table API users can skip the table registering step and can use the source/sink out-of-box. For example:

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Schema schema = new Schema()
   .column("user_id", DataTypes.BIGINT())
   .column("score", DataTypes.DECIMAL(10, 2))
   .column("ts", DataTypes.TIMESTAMP(3));
Table myKafka = tEnv.from(
   new Kafka()
      .version("0.11")
      .topic("user_logs")
      .property("bootstrap.servers", "localhost:9092")
      .property("group.id", "test-group")
      .startFromEarliest()
      .sinkPartitionerRoundRobin()
      .format(new Json().ignoreParseErrors(false))
      .schema(schema)
);
// reading from kafka table and write into filesystem table
myKafka.executeInsert(
   new Connector("filesystem")
      .option("path", "/path/to/whatever")
      .option("format", "json")
   .schema(schema)
);

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

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Proposed Changes

TableDescriptor

The current TableDescriptor will be refactored into:

/**
 * Describes a table to connect. It is a same representation of SQL CREATE TABLE DDL.
 */
@PublicEvolving
public abstract class TableDesc
riptor {

	/**
	 * Specifies the table schema.
	 */
	public TableDescriptor schema(Schema schema) {...}

	/**
	 * Specifies the partition keys of this table.
	 */
	public TableDescriptor partitionedBy(String... fieldNames) {...}

	/**
	 * Extends some parts from the original table.
	 */
	public TableDescriptor like(String originalTablePath, LikeOption... likeOptions) {...}

	/**
	 * Extends some parts from the original table.
	 */
	public TableDescriptor like(TableDescriptor originalTableDescriptor, LikeOption... likeOptions) {...}

	/**
	 * Specifies the connector options of this table, subclasses should override this method.
	 */
	protected abstract Map<String, String> connectorOptions();
}

Schema

The current Rowtime class will be removed. The current Schema class will be refactored into:

public class Schema {

	/**
	 * Adds a column with the column name and the data type.
	 */
	public Schema column(String columnName, DataType columnType) {...}

	/**
	 * Adds a computed column with the column name and the SQL expression string.
	 */
	public Schema computedColumn(String columnName, String sqlExpression) {...}

	/**
	 * Adds a processing-time column with the given column name.
	 */
	public Schema proctime(String columnName) {...}

	/**
	 * Specifies the primary key constraint for a set of given columns.
	 */
	public Schema primaryKey(String... columnNames) {...}

	/**
	 * Specifies the watermark strategy for rowtime attribute.
	 */
	public SchemaWithWatermark watermarkFor(String rowtimeColumn) {...}

	public static class SchemaWithWatermark {

		/**
		 * Specifies a custom watermark strategy using the given SQL expression string.
		 */
        public Schema as(String watermarkSqlExpr) {...}

		/**
		 * Specifies a watermark strategy for situations with monotonously ascending timestamps.
		 */
		public Schema ascendingTimestamps() {...}

		/**
		 * Specifies a watermark strategy for situations where records are out of order, but you can place
		 * an upper bound on how far the events are out of order. An out-of-order bound B means that
		 * once the an event with timestamp T was encountered, no events older than {@code T - B} will
		 * follow any more.
		 */
		public Schema boundedOutOfOrderTimestamps(Duration maxOutOfOrderness) {...}
	}
}

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

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