5c4040312b
Issue appears when one tries to create DataFrame using sqlContext.load("jdbc"...) statement when "dbtable" contains query with renamed columns.
If original column is used in SQL query once the resulting DataFrame will contain non-renamed column.
If original column is used in SQL query several times with different aliases, sqlContext.load will fail.
Original implementation of JDBCRDD.resolveTable uses getColumnName to detect column names in RDD schema.
Suggested implementation uses getColumnLabel to handle column renames in SQL statement which is aware of SQL "AS" statement.
Readings:
http://stackoverflow.com/questions/4271152/getcolumnlabel-vs-getcolumnname
http://stackoverflow.com/questions/12259829/jdbc-getcolumnname-getcolumnlabel-db2
Official documentation unfortunately a bit misleading in definition of "suggested title" purpose however clearly defines behavior of AS keyword in SQL statement.
http://docs.oracle.com/javase/7/docs/api/java/sql/ResultSetMetaData.html
getColumnLabel - Gets the designated column's suggested title for use in printouts and displays. The suggested title is usually specified by the SQL AS clause. If a SQL AS is not specified, the value returned from getColumnLabel will be the same as the value returned by the getColumnName method.
Author: Oleg Sidorkin <oleg.sidorkin@gmail.com>
Closes #6032 from osidorkin/master and squashes the following commits:
10fc44b [Oleg Sidorkin] [SPARK-7345][SQL] Regression test for JDBCSuite (resolved scala style test error)
2aaf6f7 [Oleg Sidorkin] [SPARK-7345][SQL] Regression test for JDBCSuite (renamed fields in JDBC query)
b7d5b22 [Oleg Sidorkin] [SPARK-7345][SQL] Regression test for JDBCSuite
09559a0 [Oleg Sidorkin] [SPARK-7345][SQL] Spark cannot detect renamed columns using JDBC connector
(cherry picked from commit
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hive | ||
hive-thriftserver | ||
README.md |
Spark SQL
This module provides support for executing relational queries expressed in either SQL or a LINQ-like Scala DSL.
Spark SQL is broken up into four subprojects:
- Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
- Execution (sql/core) - A query planner / execution engine for translating Catalyst’s logical query plans into Spark RDDs. This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
- Hive Support (sql/hive) - Includes an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allows users to run queries that include Hive UDFs, UDAFs, and UDTFs.
- HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.
Other dependencies for developers
In order to create new hive test cases (i.e. a test suite based on HiveComparisonTest
),
you will need to setup your development environment based on the following instructions.
If you are working with Hive 0.12.0, you will need to set several environmental variables as follows.
export HIVE_HOME="<path to>/hive/build/dist"
export HIVE_DEV_HOME="<path to>/hive/"
export HADOOP_HOME="<path to>/hadoop-1.0.4"
If you are working with Hive 0.13.1, the following steps are needed:
- Download Hive's 0.13.1 and set
HIVE_HOME
withexport HIVE_HOME="<path to hive>"
. Please do not setHIVE_DEV_HOME
(See SPARK-4119). - Set
HADOOP_HOME
withexport HADOOP_HOME="<path to hadoop>"
- Download all Hive 0.13.1a jars (Hive jars actually used by Spark) from here and replace corresponding original 0.13.1 jars in
$HIVE_HOME/lib
. - Download Kryo 2.21 jar (Note: 2.22 jar does not work) and Javolution 5.5.1 jar to
$HIVE_HOME/lib
. - This step is optional. But, when generating golden answer files, if a Hive query fails and you find that Hive tries to talk to HDFS or you find weird runtime NPEs, set the following in your test suite...
val testTempDir = Utils.createTempDir()
// We have to use kryo to let Hive correctly serialize some plans.
sql("set hive.plan.serialization.format=kryo")
// Explicitly set fs to local fs.
sql(s"set fs.default.name=file://$testTempDir/")
// Ask Hive to run jobs in-process as a single map and reduce task.
sql("set mapred.job.tracker=local")
Using the console
An interactive scala console can be invoked by running build/sbt hive/console
.
From here you can execute queries with HiveQl and manipulate DataFrame by using DSL.
catalyst$ build/sbt hive/console
[info] Starting scala interpreter...
import org.apache.spark.sql.catalyst.analysis._
import org.apache.spark.sql.catalyst.dsl._
import org.apache.spark.sql.catalyst.errors._
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.logical._
import org.apache.spark.sql.catalyst.rules._
import org.apache.spark.sql.catalyst.util._
import org.apache.spark.sql.execution
import org.apache.spark.sql.functions._
import org.apache.spark.sql.hive._
import org.apache.spark.sql.hive.test.TestHive._
import org.apache.spark.sql.types._
Type in expressions to have them evaluated.
Type :help for more information.
scala> val query = sql("SELECT * FROM (SELECT * FROM src) a")
query: org.apache.spark.sql.DataFrame = org.apache.spark.sql.DataFrame@74448eed
Query results are DataFrames
and can be operated as such.
scala> query.collect()
res2: Array[org.apache.spark.sql.Row] = Array([238,val_238], [86,val_86], [311,val_311], [27,val_27]...
You can also build further queries on top of these DataFrames
using the query DSL.
scala> query.where(query("key") > 30).select(avg(query("key"))).collect()
res3: Array[org.apache.spark.sql.Row] = Array([274.79025423728814])