String concatenation should low priority than other operators

spark-sql> explain select 'four: ' || 2 + 2;
== Physical Plan ==
*(1) Project [null AS (CAST(concat(four: , CAST(2 AS STRING)) AS DOUBLE) + CAST(2 AS DOUBLE))#2]
+- Scan OneRowRelation[]
spark-sql> select 'four: ' || 2 + 2;
NULL

hive> select 'four: ' || 2 + 2;
OK
four: 4