Usage of (case, when) in PostgreSQL

1.case when

(
        case
        when substr(starttime::varchar,0,5)='2020'  then '2020 year '
        when substr(starttime::varchar,0,5)='2019'  then '2019 year '
        when substr(starttime::varchar,0,5)='2018'  then '2018 year '
        when substr(starttime::varchar,0,5)='2017'  then '2017 year '
        when substr(starttime::varchar,0,5)='2016'  then '2016 year '
        when substr(starttime::varchar,0,5)='2015'  then '2015 year '
        when substr(starttime::varchar,0,5)='2014'  then '2014 year '
        when substr(starttime::varchar,0,5)='2013'  then '2013 year '
        when substr(starttime::varchar,0,5)='2012'  then '2012 year '
        when substr(starttime::varchar,0,5)='2011'  then '2011 year '
        when substr(starttime::varchar,0,5)='2010'  then '2010 year '
        when starttime is null then ' Other years ' end
 ) AS year

2.mybatis To determine whether a parameter is empty

<if test="geojsonString !=null and geojsonString !=''">
            WHERE
            st_intersects(geom,st_geomfromgeojson(#{
    geojsonString}))
</if>