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Posted to commits@doris.apache.org by GitBox <gi...@apache.org> on 2019/11/05 10:01:56 UTC
[GitHub] [incubator-doris] imay commented on a change in pull request #2127:
Support aggregation type of REPLACE_IF_NOT_NULL
imay commented on a change in pull request #2127: Support aggregation type of REPLACE_IF_NOT_NULL
URL: https://github.com/apache/incubator-doris/pull/2127#discussion_r342473682
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File path: docs/documentation/cn/sql-reference/sql-statements/Data Definition/CREATE TABLE.md
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@@ -55,9 +55,12 @@
BITMAP 列只能通过配套的 BITMAP_UNION、BITMAP_COUNT、TO_BITMAP 进行查询或使用
agg_type：聚合类型，如果不指定，则该列为 key 列。否则，该列为 value 列
- SUM、MAX、MIN、REPLACE、HLL_UNION(仅用于HLL列，为HLL独有的聚合方式)、
- BITMAP_UNION(仅用于 BITMAP 列，为 BITMAP 独有的聚合方式)
- 该类型只对聚合模型(key_desc的type为AGGREGATE KEY)有用，其它模型不需要指定这个。
+
+ * SUM、MAX、MIN、REPLACE
+ * HLL_UNION(仅用于HLL列，为HLL独有的聚合方式)、
+ * BITMAP_UNION(仅用于 BITMAP 列，为 BITMAP 独有的聚合方式)、
+ * REPLACE_IF_NOT_NULL：这个聚合类型的含义是当且仅当新导入数据是非NULL值时才会发生替换行为，如果新导入的数据是NULL，那么Doris仍然会保留原值。注意：如果用户在建表时REPLACE_IF_NOT_NULL列指定了NOT NULL，那么Doris仍然会将其转化为NULL，不会向用户报错。用户可以借助这个类型完成部分列导入的功能。
Review comment:
Because NOT NULL is useless for this aggregation method. If we throw an exception here, there is no option for user. So I think we can make it `NULL` to make user easy to use.
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