The max/min function used by AggrStats for decimal type is not what we expected

In current version hive-schema-1.2.0, in TABLE PART_COL_STATS, we store the "BIG_DECIMAL_LOW_VALUE" and "BIG_DECIMAL_HIGH_VALUE" as varchar. For example,

derby
"BIG_DECIMAL_LOW_VALUE" VARCHAR(4000), "BIG_DECIMAL_HIGH_VALUE" VARCHAR(4000)

mssql
BIG_DECIMAL_HIGH_VALUE varchar(255) NULL,
BIG_DECIMAL_LOW_VALUE varchar(255) NULL,

mysql
`BIG_DECIMAL_LOW_VALUE` varchar(4000) CHARACTER SET latin1 COLLATE latin1_bin,
`BIG_DECIMAL_HIGH_VALUE` varchar(4000) CHARACTER SET latin1 COLLATE latin1_bin,

oracle
BIG_DECIMAL_LOW_VALUE VARCHAR2(4000),
BIG_DECIMAL_HIGH_VALUE VARCHAR2(4000),

postgres
"BIG_DECIMAL_LOW_VALUE" character varying(4000) DEFAULT NULL::character varying,
"BIG_DECIMAL_HIGH_VALUE" character varying(4000) DEFAULT NULL::character varying,

And, when we do the aggrstats, we do a MAX/MIN of all the BIG_DECIMAL_HIGH_VALU/BIG_DECIMAL_LOW_VALUEE of partitions. We are expecting a max/min of a decimal (a number). However, it is actually a max/min of a varchar (a string). As a result, '900' is more than '1000'. This also affects the extrapolation of the status. The proposed solution is to use a CAST function to cast it to decimal.