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Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]

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Released: <Flink Version>

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Motivation

To support connectors in avoiding overwriting non-target columns with null values when processing partial column updates, we propose adding information on the target column list to DynamicTableSink#Context.

FLINK-18726 supports inserting statements with specified column list, it fills null values (or potentially declared default values in the future) for columns not appearing in the column list of insert statement to the target table. While in the field of big data, But this behavior does not satisfy the some partial column update requirements of some storage systems which allow storing null values.

Let's explain the scenario further, denormalized table(or the commonly known 'wide table') model is a common data modeling method, which connects multiple tables to form a unified wide table to improve query and analysis efficiency.
The data of wide denormalized table comes from different source tables. When writing or updating data, it usually adopts the mode of specifying the column list to write.

For example, there is a wide denormalized table t1 which has a primary key `a`:

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where column b, c, d from s1 table, column e, f, g from s2 table,
by different processing data from the source table s1 and s2,  the two insertions specify a different column list written to the wide denormalized table, ideally the two insertions will not affect each others' column

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The current connector implementor has no way of knowing that the last three fields were added by the planner and not from real user data. The user has to declare several different schemas (containing only partial column information and no overlap except for the primary key) to get around the current problem. 

By adding targetColumnList target column list information to the DynamicTableSink#Context, this problem can be solved.

Public Interfaces

Add new getTargetColumnList new getTargetColumns to DynamicTableSink#Context.

        /**
         * Returns the an {@link Optional} array of column index paths related to user specified target
         * column name list or an empty list {@link Optional#empty()} when not specified. The array indices are 0-based
         * and support composite columns within (possibly nested) structures.
         *
         * <p>This information comes from the column list of the DML clause, e.g., for a sink table
         * t1 which schema is: {@code a STRING, b ROW < b1 INT, b2 STRING>, c BIGINT}
         *
         * <ul>
         *   <li>insert: 'insert into targett1(a, b, c.b2) ...', the column list will be 'a, b.b2', c'.and thewill
         *       column list will be empty forreturn {@code [[0], [1, 1]]}. The statement 'insert into target select ...' without
         *       specifying a column list will return {@link Optional#empty()}.
         *   <li>update: 'update target set a=1, b.b1=2 where ...', the column list will be 'a,
         *       b.b1', will return {@code [[0], [1, 0]]}.
         * </ul>
         *
         * <p>Note: the column list will always bereturn empty infor the delete clause statement because it has no column list.
         */
            List<String> getTargetColumnListOptional<int[][]> getTargetColumns();

Proposed Changes

The internal SinkRuntimeProviderContext will support new constructor with targetColumnList targetColumns param, this can be used by connectors to recognize the user-specified column list.

Note: currently nested columns in column list of an insert/update statement is unsupported (as described in FLINK-31301 & FLINK-31344), so we can make this flip support simple columns first and then support nested columns after FLINK-31301 & FLINK-31344 fixed. 

Compatibility, Deprecation, and Migration Plan

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