Harleen Singh Mann created SPARK-23370:

             Summary: Spark receives a size of 0 for an Oracle Number field 
defaults the field type to be BigDecimal(30,10)
                 Key: SPARK-23370
                 URL: https://issues.apache.org/jira/browse/SPARK-23370
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.2.1
         Environment: Spark 2.2

Oracle 11g

JDBC ojdbc6.jar
            Reporter: Harleen Singh Mann

Currently, on jdbc read spark obtains the schema of a table from using 
{color:#654982} resultSet.getMetaData.getColumnType{color}

This works 99.99% of the times except when the column of Number type is added 
on an Oracle table using the alter statement. This is essentially an Oracle DB 
+ JDBC bug that has been documented on Oracle KB and patches exist. [oracle 

{color:#FF0000}As a result of the above mentioned issue, Spark receives a size 
of 0 for the field and defaults the field type to be BigDecimal(30,10) instead 
of what it actually should be. This is done in OracleDialect.scala. This may 
cause issues in the downstream application where relevant information may be 
missed to the changed precision and scale.{color}

_The versions that are affected are:_ 
_JDBC - Version: and later   [Release: 11.2 and later ]_
_Oracle Server - Enterprise Edition - Version: to  
_[Release: 11.1 to 11.2]_ 

+Proposed approach:+

There is another way of fetching the schema information in Oracle: Which is 
through the all_tab_columns table. If we use this table to fetch the precision 
and scale of Number time, the above issue is mitigated.


{color:#14892c}I can implement the changes, but require some inputs on the 
approach from the gatekeepers here.{color}
{color:#14892c}PS. This is also my first Jira issue and my first fork for 
Spark, so I will need some guidance along the way. (yes, I am a newbee to this) 

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