[GitHub] [spark] dilipbiswal opened a new pull request #24532: [SPARK-27596] The JDBC 'query' option doesn't work for Oracle database

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dilipbiswal opened a new pull request #24532: [SPARK-27596] The JDBC 'query' option doesn't work for Oracle database
URL: https://github.com/apache/spark/pull/24532
 
 
   ## What changes were proposed in this pull request?
   **Description from JIRA**
   For the JDBC option `query`, we use the identifier name to start with underscore: s"(${subquery}) _SPARK_GEN_JDBC_SUBQUERY_NAME${curId.getAndIncrement()}". This is not supported by Oracle.
   The Oracle doesn't seem to support identifier name to start with non-alphabet character (unless it is quoted) and has length restrictions as well. [link](https://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements008.htm)
   
   In this PR, the generated alias name 'SPARK_GEN_JDBC_SUBQUERY_NAME<int value>' is fixed to remove "_" prefix and also the alias name is shortened to not exceed the identifier length limit.
   
   ## How was this patch tested?
   Tests are added for MySql, Postgress, Oracle and DB2 to ensure enough coverage.

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