[HIVE-13812] Changing column from float to string group type will drop some factional digits

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.2.1
• Target Version/s: 1.2.1
• Assignee: Unassigned
• Reporter: Takahiko Saito
• Created: 20/May/16 21:14
• Updated: 20/May/16 21:15

Description

Create a textfile table with a float column and insert some values:

0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> create table test(f float);
No rows affected (0.237 seconds)
0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> insert into table test values(-35664.76171875),(29497.349609375);
INFO  : Session is already open
INFO  : Dag name: insert into table tes...5),(29497.349609375)(Stage-1)
INFO  :

INFO  : Status: Running (Executing on YARN cluster with App id application_1463771904371_0006)

INFO  : Map 1: 0/1
INFO  : Map 1: 0/1
INFO  : Map 1: 0/1
INFO  : Map 1: 0(+1)/1
INFO  : Map 1: 1/1
INFO  : Loading data to table default.test from hdfs://os-r6-pxwhrs-hiveserver2-3re-5.openstacklocal:8020/apps/hive/warehouse/test/.hive-staging_hive_2016-05-20_21-06-29_377_6487823927119226603-10/-ext-10000
INFO  : Table default.test stats: [numFiles=1, numRows=2, totalSize=19, rawDataSize=17]
No rows affected (11.069 seconds)
0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> select * from test;
+------------------+--+
|      test.f      |
+------------------+--+
| -35664.76171875  |
| 29497.349609375  |
+------------------+--+
2 rows selected (0.137 seconds)
0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> describe test;
+-----------+------------+----------+--+
| col_name  | data_type  | comment  |
+-----------+------------+----------+--+
| f         | float      |          |
+-----------+------------+----------+--+
1 row selected (0.173 seconds)

Then change float type to string successfully, but when you select table, some fractional digits are lost:

0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> alter table test change column f f string;
No rows affected (0.214 seconds)
0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> describe test;
+-----------+------------+----------+--+
| col_name  | data_type  | comment  |
+-----------+------------+----------+--+
| f         | string     |          |
+-----------+------------+----------+--+
1 row selected (0.151 seconds)
0: jdbc:hive2://os-r6-pxwhrs-hiveserver2-3re-> select * from test;
+------------+--+
|   test.f   |
+------------+--+
| -35664.76  |
| 29497.35   |
+------------+--+
2 rows selected (0.141 seconds)