fix: better error message when users enter old style syntax for query #3397

big-andy-coates · 2019-09-23T11:39:45Z

Description

Say a user executes SELECT * FROM X JOIN Y ON X.ID = Y.ID; or similar. In older versions of KSQL this would be a streaming join and would work. With the introduction of static queries this example is now a static query, which don't support joins. Hence the user will get the error: Static queries do not support joins... which isn't very helpful if you don't know the query syntax has changed. With this PR the output is now:

Static queries do not support joins. Did you mean to execute a continuous query? Add an 'EMIT CHANGES' clause to do so.

Query syntax in KSQL has changed. There are now two broad categories of queries:
- Static queries: query the current state of the system, return a result and terminate.
- Streaming queries: query the state of the system in motion and will continue to output results until they meet any LIMIT clause criteria or are terminated by the user.

'EMIT CHANGES' is used to indicate a query is continuous and outputs all changes. To turn a static query into a streaming query, as was the default in older versions of KSQL, add `EMIT CHANGES` to the end of the statement before any limit clause.

For example, the following are static queries:
	'SELECT * FROM X WHERE ROWKEY=Y;' (non-windowed table)
	'SELECT * FROM X WHERE ROWKEY=Y AND WINDOWSTART>=Z;' (windowed table)

and, the following is a streaming query:
	'SELECT * FROM X EMIT CHANGES;'

Note: Persistent queries, e.g. `CREATE TABLE AS ...`, currently have an implicit `EMIT CHANGES`. However, it is recommended to add `EMIT CHANGES` to such statements going forward, as a this will be required in a future release.

Testing done

usual

Reviewer checklist

Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
Ensure relevant issues are linked (description should include text like "Fixes #")

Say a user executes `SELECT * FROM X JOIN Y ON X.ID = Y.ID;` or similar. In older versions of KSQL this would be a streaming join and would work. With the introduction of static queries this example is now a static query, which don't support joins. Hence the user will get the error: `Static queries do not support joins`... which isn't very helpful if you don't know the query syntax has changed. With this PR the output is now: ``` Static queries do not support joins. Did you mean to execute a continuous query? If so, add an 'EMIT CHANGES' clause. Query syntax in KSQL has changed. There are now two broad categories of queries: - Static queries: query the current state of the system, return a result and terminate. - Streaming queries: query the state of the system in motion and will continue to output results until they meet any LIMIT clause criteria or are terminated by the user. 'EMIT CHANGES' is used to indicate a query is continuous and outputs all changes. To turn a static query into a streaming query, as was the default in older versions of KSQL, add `EMIT CHANGES` to the end of the statement before any limit clause. For example, the following are static queries: 'SELECT * FROM X WHERE ROWKEY=Y;' (non-windowed table) 'SELECT * FROM X WHERE ROWKEY=Y AND WINDOWSTART>=Z;' (windowed table) and, the following is a streaming query: 'SELECT * FROM X EMIT CHANGES;' Note: Persistent queries, e.g. `CREATE TABLE AS ...`, currently have an implicit `EMIT CHANGES`. However, it is recommended to add `EMIT CHANGES` to such statements going forward, as a this will be required in a future release. ```

big-andy-coates · 2019-09-23T11:40:34Z

@JimGalasyn, fancy correctly my terrible english in the above message? :D

vcrfxia

Thanks @big-andy-coates -- this is great!

ksql-engine/src/main/java/io/confluent/ksql/analyzer/ContinuousQueryValidator.java

ksql-engine/src/main/java/io/confluent/ksql/analyzer/StaticQueryValidator.java

…sQueryValidator.java Co-Authored-By: Jim Galasyn <[email protected]>

…ryValidator.java Co-Authored-By: Jim Galasyn <[email protected]>

ksql-engine/src/main/java/io/confluent/ksql/analyzer/StaticQueryValidator.java

JimGalasyn

LGTM, with a few suggestions.

…ryValidator.java Co-Authored-By: Jim Galasyn <[email protected]>

# Conflicts: # ksql-engine/src/main/java/io/confluent/ksql/analyzer/StaticQueryValidator.java

big-andy-coates added 2 commits September 23, 2019 12:24

chore: improve msg

d19b3a0

big-andy-coates requested a review from a team as a code owner September 23, 2019 11:39

big-andy-coates requested a review from JimGalasyn September 23, 2019 11:40

vcrfxia approved these changes Sep 23, 2019

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vcrfxia requested a review from a team September 23, 2019 14:17