Unable to specify dynamic time range in sql query for jdbc river in elasticsearch

I am using the jdbc river for elasticsearch to index mysql table data.

My River:

 curl -XPUT 'localhost:9200/_river/river_mention_reports/_meta' -d '{
	"type" : "jdbc",
	"jdbc" : {
	    "driver" : "com.mysql.jdbc.Driver",
	    "url" : "jdbc:mysql://localhost:3306/ESTest1_development",
	    "user" : "root",
	    "password" : "password",
	    "sql" : "select * from table where creation_time >= (NOW() - INTERVAL 2 MINUTE)",
	    "poll" : "2m",
	    "versioning" : false
	"index" : {
	    "index" : "monitoring",
	    "type" : "mention_reports"

SQL query that I have specified in the river is:

select * from table where creation_time >= (NOW() - INTERVAL 2 MINUTE)

Now the problem is, the river after every poll removes the data that was indexed outside the time range(current minus 2 minutes) specified in the query, instead of adding fresh data to the index. The reason I have specified a time range is because I don't want the river to reindex the entire dataset again and again.