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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