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https://issues.apache.org/jira/browse/SPARK-24423?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16494753#comment-16494753
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Dilip Biswal commented on SPARK-24423:
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[~smilegator] Thanks Sean for pinging me. I would like to take a look at this
one.
> Add a new option `query` for JDBC sources
> -----------------------------------------
>
> Key: SPARK-24423
> URL: https://issues.apache.org/jira/browse/SPARK-24423
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.3.0
> Reporter: Xiao Li
> Priority: Major
>
> Currently, our JDBC connector provides the option `dbtable` for users to
> specify the to-be-loaded JDBC source table.
>
> val jdbcDf = spark.read
> .format("jdbc")
> .option("*dbtable*", "dbName.tableName")
> .options(jdbcCredentials: Map)
> .load()
>
> Normally, users do not fetch the whole JDBC table due to the poor
> performance/throughput of JDBC. Thus, they normally just fetch a small set of
> tables. For advanced users, they can pass a subquery as the option.
>
> val query = """ (select * from tableName limit 10) as tmp """
> val jdbcDf = spark.read
> .format("jdbc")
> .option("*dbtable*", query)
> .options(jdbcCredentials: Map)
> .load()
>
> However, this is straightforward to end users. We should simply allow users
> to specify the query by a new option `query`. We will handle the complexity
> for them.
>
> val query = """select * from tableName limit 10"""
> val jdbcDf = spark.read
> .format("jdbc")
> .option("*{color:#ff0000}query{color}*", query)
> .options(jdbcCredentials: Map)
> .load()
>
> Users are not allowed to specify query and dbtable at the same time.
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