Some use has the requirment that only some of columns will be update in
one load operation, and others will retain as original. However, Doris
can't handle this situation, because user must specify value for all
columns. Then if a column aggregation method is REPLACE, use must query
original value to overwrite it. This often needs some work for user to
do.
If this CL is applied, user can use REPLACE_IF_NOT_NULL instead of
REPLACE. Then when load data to table, if user don't intent to change
value of this column, user can specify NULL for this column. Doris will
retain original value for this column.
Add a new type: Object. Currently, it's mainly for complex aggregate metrics(HLL , Bitmap).
The Object type has the following constraints：
1 Object type could not as key column type
2 Object type doesn't support all indices (BloomFilter, short key, zone map, invert index)
3 Object type doesn't support filter and group by
In the implementation：
The Object type reuse the StringValue and StringVal, because in storage engine, the Object type is binary, it has a pointer and length.
The prepare/close step of scalar function is already supported in execution framework, We only need to do is that support it in syntax and meta in frontend.
In addition, 'Hive' binary type of scalar function NOT supports prepare/close step, we need to make it supports.
Random distribution is no longer supported since version 0.9.
And we need a way to convert the random distribution to hash distribution.
ALTER TABLE db.tbl SET ("distribution_type" = "hash");
