twalthr commented on a change in pull request #11692: [FLINK-16992][table-common] Add all ability interfaces for table sources and sinks URL: https://github.com/apache/flink/pull/11692#discussion_r410306261
########## File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/connector/source/abilities/SupportsProjectionPushDown.java ########## @@ -0,0 +1,72 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.flink.table.connector.source.abilities; + +import org.apache.flink.annotation.PublicEvolving; +import org.apache.flink.table.connector.source.ScanTableSource; + +/** + * Enables to push down a (possibly nested) projection into a {@link ScanTableSource}. + * + * <p>Given the following SQL: + * <pre>{@code + * CREATE TABLE t (i INT, r ROW < d DOUBLE, b BOOLEAN>, s STRING); + * SELECT s, r.d FROM t; + * }</pre> + * + * <p>In the above example, {@code r.d} and {@code s} are required fields. Other fields can be skipped + * in a projection. + * + * <p>By default, if this interface is not implemented, a projection is applied in a subsequent operation + * after the source. + * + * <p>For efficiency, a source can push a projection further down in order to be close to the actual + * data generation. A projection is only selecting fields that are used by a query. It does neither + * reorder fields nor contain any computation. A projection can either be performed on the fields of + * the top-level row only or consider nested fields as well (see {@link #supportsNestedProjection()}). + * + * <p>Note: If a source implements {@link SupportsComputedColumnPushDown}, the projection must be applied Review comment: I hope this is clearer now: ``` * <p>Note: If a source implements {@link SupportsComputedColumnPushDown}, the projection must be applied * to the physical data in the first step. The {@link SupportsComputedColumnPushDown} (already aware of the projection) * will then use the projected physical data and insert computed columns into the result. ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
