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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2019/07/16 09:39:14 UTC
[GitHub] [spark] maropu commented on issue #25137: [SPARK-28348][SQL]
Decimal precision promotion for binary arithmetic with casted decimal type
maropu commented on issue #25137: [SPARK-28348][SQL] Decimal precision promotion for binary arithmetic with casted decimal type
URL: https://github.com/apache/spark/pull/25137#issuecomment-511744139
Which one does follow the SQL standard? IIUC the current spark behaviour depends on the Hive one. On the other hand, PostgreSQL officially says [they follows the standard of "Implicit casting among the numeric data types](https://www.postgresql.org/docs/11/features-sql-standard.html) and the result is;
```
postgres=# select cast(c1 * cast(-34338492.215397047 as decimal(38, 18)) as decimal(38, 18)) as c1 from spark_28348;
c1
-------------------------------------
1179132047626883.596862135856320209
(1 row)
postgres=# explain verbose select cast(c1 * cast(-34338492.215397047 as decimal(38, 18)) as decimal(38, 18)) as c1 from spark_28348;
QUERY PLAN
-----------------------------------------------------------------------------------
Seq Scan on public.spark_28348 (cost=0.00..31.00 rows=1400 width=30)
Output: ((c1 * '-34338492.215397047000000000'::numeric(38,18)))::numeric(38,18)
(2 rows)
```
mysql has the same result;
```
mysql> select cast(c1 * cast(-34338492.215397047 as decimal(38, 18)) as decimal(38, 18)) as c1 from spark_28348;
+-------------------------------------+
| c1 |
+-------------------------------------+
| 1179132047626883.596862135856320209 |
+-------------------------------------+
```
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