[IMPALA-10321] Add a query option to get approximation when decimal value not fit column precision and scale

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Backend
• Epic Color: ghx-label-3
• Assignee: Unassigned
• Reporter: Sheng Wang
• Created: 12/Nov/20 08:22
• Updated: 12/Nov/20 08:22

Description

Currently, for text-based formats with decimal type, Impala will return {{NULL }}if values do not fit within the precision and scale, but hive will return a approximation. For example, we execute following statements:

 

create table text_decimals (x string);
insert into text_decimals values ("1"), ("2"), ("99.99"), ("1.234"), ("000001"), ("1.000000000");
alter table text_decimals replace columns (x decimal(4,2));

If we query table by Impala, we will get NULL for line 4 and 6, but if we use Hive, we can get  1.23 and 1.00. So shall we add a new query option to control approximate calculation? If we set true, Impala will also return approximation like Hive, if set false, return NULL.