hadoop - 删除配置单元分区的外部表但保留分区

Question

使用外部配置单元表时，有没有一种方法可以删除目录中的数据，但通过查询保留分区。请注意我不想删除表并重新创建它。我只想清空底层文件夹并重新开始一个过程。我的表很大，按年、月、日和小时分区，手动重新创建分区需要很多时间。

谢谢

Answer 1

truncate table ... 删除所有数据。
truncate table partition (...) 删除特定分区的数据。

保留目录结构。

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首先应该将外部表转换为管理表，例如

alter table t set tblproperties('EXTERNAL'='FALSE');

完成后，我们可以将其转换回来

alter table t set tblproperties('EXTERNAL'='TRUE');

---

演示

create table t (i int) partitioned by (x char(1));
set hive.exec.dynamic.partition.mode=nonstrict;
insert into t partition (x) values (1,'A'),(2,'B'),(3,'C');
alter table t set tblproperties('EXTERNAL'='TRUE');

---

select * from t;

---

+-----+-----+
| t.i | t.x |
+-----+-----+
|   1 | A   |
|   2 | B   |
|   3 | C   |
+-----+-----+

---

dfs -ls -R /user/hive/warehouse/t;

---

drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:40 /user/hive/warehouse/t/x=A
-rwxrwxrwx   1 cloudera supergroup          2 2017-03-28 11:40 /user/hive/warehouse/t/x=A/000000_0
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:40 /user/hive/warehouse/t/x=B
-rwxrwxrwx   1 cloudera supergroup          2 2017-03-28 11:40 /user/hive/warehouse/t/x=B/000000_0
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:40 /user/hive/warehouse/t/x=C
-rwxrwxrwx   1 cloudera supergroup          2 2017-03-28 11:40 /user/hive/warehouse/t/x=C/000000_0

---

truncate table t partition (x='B');

FAILED: SemanticException [Error 10146]: Cannot truncate non-managed table t.

alter table t set tblproperties('EXTERNAL'='FALSE');

---

truncate table t partition (x='B');

---

select * from t;

---

+-----+-----+
| t.i | t.x |
+-----+-----+
|   1 | A   |
|   3 | C   |
+-----+-----+

---

dfs -ls -R /user/hive/warehouse/t;

---

drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:40 /user/hive/warehouse/t/x=A
-rwxrwxrwx   1 cloudera supergroup          2 2017-03-28 11:40 /user/hive/warehouse/t/x=A/000000_0
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:42 /user/hive/warehouse/t/x=B
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:40 /user/hive/warehouse/t/x=C
-rwxrwxrwx   1 cloudera supergroup          2 2017-03-28 11:40 /user/hive/warehouse/t/x=C/000000_0

---

truncate table t;

---

+-----+-----+
| t.i | t.x |
+-----+-----+

---

dfs -ls -R /user/hive/warehouse/t;

---

drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:43 /user/hive/warehouse/t/x=A
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:43 /user/hive/warehouse/t/x=B
drwxrwxrwx   - cloudera supergroup          0 2017-03-28 11:43 /user/hive/warehouse/t/x=C

---

alter table t set tblproperties('EXTERNAL'='TRUE');