When i tried enclosing the param_end with double quote, i get following error:

```org.apache.spark.SparkDateTimeException: [CAST_INVALID_INPUT] The value '' of the type "STRING" cannot be cast to "TIMESTAMP" because it is malformed. Correct the value as per the syntax, or change its target type. Use `try_cast` to tolerate malformed input and return NULL instead. If necessary set "spark.sql.ansi.enabled" to "false" to bypass this error.

Then I tried with cast function on the param_end to convert it to TIMESTAMP. This works now.

Alternatively, i have managed to create a dataframe and append it to the delta table, instead of using the spark.sql(). This is much simpler.