title: How to generate a spark sql truncate query without Only
body: <p>I am using Spark(3.0.0_preview) and reading/writing from/to GreenPlum(version 5.24). The Greenplum version 5.24 doesn't support the "truncate table <strong>only</strong> $table_name" command.</p>
  
  <p>With Spark 3.0.0_preview and jdbcdriver(org.postgresql" % "postgresql" % "42.2.5), the command genearted by Spark is "truncate table <strong>only</strong> $table_name".</p>
  
  <pre><code> df.write.format("jdbc").option("url", "jdbc:postgresql://test:5432/sample")
  .option("user", "sample")
  .option("password", "sample")
  .option("dbtable", "test.employer")
  .option("truncate", true) // **Genearte truncate table only**
  .mode(SaveMode.Overwrite)
  .save();
  </code></pre>
  
  <p>I want to generate truncate command without ONLY option. As the only option is not supported by Greenplum V5.24</p>