Docs: improve KEY and TIMESTAMP descriptions for CREATE STREAM and CREATE TABLE #1094
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miguno
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| @@ -4,23 +4,27 @@ | |||
| Message Keys | |||
| ============ | |||
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| The `CREATE STREAM` and `CREATE TABLE` statements allow the user to specify the column that corresponds to the Kafka message key by setting the `KEY` property of the `WITH` clause. For example: | |||
| The ``CREATE STREAM`` and ``CREATE TABLE`` statements, which read data from a Kafka topic into a stream or table, allow you to specify a field/column in the Kafka message value that corresponds to the Kafka message key by setting the ``KEY`` property of the ``WITH`` clause. | |||
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This still doesn't sound right to me. I thought the KEY property allowed a user to map the key of the message in Kafka to a column in the KSQL stream's/table's schema.
Have I got the wrong end of the stick?
The KEY is described in the syntax-reference.rst as:
Associates the message key in the Kafka topic with a column in the KSQL table. You must be
sure that the record key corresponds to the value in the key column and is in the right
format. For more information, see :ref:ksql_key_constraints
Which, if I'm honest, just doesn't make sense to me. When I read this I think that, by supplying WITH( KEY = "foo" ) then the value within each records key will be stored in the column called foo. But if that is true, then:
You must be sure that the record key corresponds to the value in the key column
Makes no sense, as they will always be the same, because KSQL is loading the record key into the key column.
I'm confused ! ;)
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I thought the KEY property allowed a user to map the key of the message in Kafka to a column in the KSQL stream's/table's schema.
Alas no. It would be great if it did, see #804. The key must currently be present in BOTH the message key and "somewhere" in the message value as well (= "duplicate key" requirement).
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