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https://issues.apache.org/jira/browse/HIVE-13812?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Takahiko Saito updated HIVE-13812:
----------------------------------
    Description: 
Create a textfile table with a float column and insert some values:
{noformat}
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)
{noformat}

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

  was:
Create a table with a float column and insert some values:
{noformat}
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)
{noformat}

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


> Change column from float to string group type will drop some factional digits
> -----------------------------------------------------------------------------
>
>                 Key: HIVE-13812
>                 URL: https://issues.apache.org/jira/browse/HIVE-13812
>             Project: Hive
>          Issue Type: Bug
>    Affects Versions: 1.2.1
>            Reporter: Takahiko Saito
>
> Create a textfile table with a float column and insert some values:
> {noformat}
> 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)
> {noformat}
> Then change float type to string successfully, but when you select table, 
> some fractional digits are lost:
> {noformat}
> 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)
> {noformat}



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