refactored the query because postgress automatically converts unquoted column names to lowercase

Author: itsankit-google

database-commons/src/main/java/io/cdap/plugin/db/batch/sink/AbstractDBSink.java

@@ -305,18 +305,20 @@ private void validateSchema(FailureCollector collector, Class<? extends Driver>
           return;
         }
       }
-
-      try (PreparedStatement pStmt = connection.prepareStatement("SELECT * FROM " + dbSinkConfig.getEscapedTableName()
-                                                                   + " WHERE 1 = 0");
+      setColumnsInfo(inputSchema.getFields());
+      try (PreparedStatement pStmt = connection.prepareStatement(String.format("SELECT %s FROM %s WHERE 1 = 0",
+                                                                               dbColumns,
+                                                                               dbSinkConfig.getEscapedTableName()));
            ResultSet rs = pStmt.executeQuery()) {
         getFieldsValidator().validateFields(inputSchema, rs, collector);
       }
     } catch (SQLException e) {
       LOG.error("Exception while trying to validate schema of database table {} for connection {}.",
                 tableName, connectionString, e);
       collector.addFailure(
-        String.format("Exception while trying to validate schema of database table '%s' for connection '%s'.",
-                      tableName, connectionString), null).withStacktrace(e.getStackTrace());
+        String.format("Exception while trying to validate schema of database table '%s' for connection '%s' with %s",
+                      tableName, connectionString, e.getMessage()),
+        null).withStacktrace(e.getStackTrace());
     }
   }