Status

Current state: Under discussion

Discussion thread: http://apache-flink-mailing-list-archive.1008284.n3.nabble.com/DISCUSS-FLIP-110-Support-LIKE-clause-in-CREATE-TABLE-td38378.html

JIRA:

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

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CREATE [ TEMPORARY ] TABLE [ IF NOT EXISTS ] table_name ( [
  {   column
    | table_constraint
    [, ... ]
] )
[ WITH ( table_properties ) ]
[ LIKE parent_table [ like_options ] } ]

where like_options are:

  { INCLUDING | EXCLUDING } ALL
| [{ 
     { INCLUDING | EXCLUDING } { CONSTRAINTS }
   | { INCLUDING | EXCLUDING | OVERWRITING } { GENERATED | OPTIONS } }
   [, ...]
  ]

...

CONSTRAINTS | INDEXES | STORAGE | COMMENTS | ALL

I suggest supporting INCLUDING/EXCLUDINGlike-options:

• ALL
• CONSTRAINTS: primary keys, unique key, does not include NOT NULL constraint (in Flink it's part of the type)
  
• GENERATED: computed columns and watermarks
  
• OPTIONS: connector properties in WITH (...) clause
  
• PARTITIONS: partitions definition

Additionally I suggest supporting different INCLUDING/EXCLUDING like-options strategies:

• INCLUDING (default -> fail on duplicate keys)
• EXCLUDING
• OVERWRITING (any explicit options/columns overwrite options/columns from base source, overwriting happens in the order the LIKE clauses were declared)
  

The supported combinations would be:

	INCLUDING	EXCLUDING	OVERWRITING
ALL
CONSTRAINTS
PARTITIONS
GENERATED
OPTIONS

The reason why I suggest not to support OVERWRITING CONSTRAINTS is that usually it's rather hard to overwrite only some of the constraints. If the constraint(primary key, unique key) from the base table does not apply to the derived table, in my opinion it is safer to exclude all constraints and redefine them.  We could revisit that in the future, if we see a need to support also OVERWRITING for constraints. The same applies for PARTITIONS.

Default options:

    INCLUDING ALL = INCLUDING CONSTRAINTS

                                       INCLUDING GENERATED

                                       INCLUDING PARTITIONS

                                       INCLUDING OPTIONS

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CREATE [TEMPORARY] TABLE base_table_1 (
    id BIGINT,
    name STRING,
    tstmp TIMESTAMP,
	PRIMARY KEY(id)
) WITH (
    ‘connector’: ‘kafka’,
    ‘connector.starting-offset’: ‘12345’,
    ‘format’: ‘json’
)

CREATE [TEMPORARY] TABLE derived_table (
    WATERMARK FOR tstmp AS tsmp - INTERVAL '5' SECOND
)
LIKE base_table (OVERWRITING OPTIONS, EXCLUDING CONSTRAINTS)
WITH (
    ‘connector.starting-offset’: ‘0’
)
LIKE base_table (OVERWRITING OPTIONS, EXCLUDING CONSTRAINTS)

The derived_table will be equivalent to:

CREATE [TEMPORARY] TABLE derived_table (
    id BIGINT,
    name STRING,
    tstmp TIMESTAMP,
    WATERMARK FOR tstmp AS tsmp - INTERVAL '5' SECOND
) WITH (
    ‘connector’: ‘kafka’,
    ‘connector.starting-offset’: ‘0’,
    ‘format’: ‘json’
)

Merging columns of the original table

The columns of the original table shall be appended to the columns defined in the current statement. If the are columns with the same name in both tables an exception will be thrown.

Support in Table API

Support of that feature in Table API will require a separate FLIP, as the connect API requires a rework anyway.

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