GitHub user jiangxb1987 opened a pull request:
https://github.com/apache/spark/pull/21074
[SPARK-21811][SQL] Fix the inconsistency behavior when finding the widest
common type
## What changes were proposed in this pull request?
Currently we find the wider common type by comparing the two types from
left to right, this can be a problem when you have two data types which don't
have a common type but each can be promoted to StringType.
For instance, if you have a table with the schema:
[c1: date, c2: string, c3: int]
The following succeeds:
SELECT coalesce(c1, c2, c3) FROM table
While the following produces an exception:
SELECT coalesce(c1, c3, c2) FROM table
This is only a issue when the seq of dataTypes contains `StringType` and
all the types can do string promotion.
close #19033
## How was this patch tested?
Add test in `TypeCoercionSuite`
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/jiangxb1987/spark typeCoercion
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/21074.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #21074
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commit 803a6a443ba9f7d3dc34d68b0d15f53c1b6054fb
Author: Xingbo Jiang <xingbo.jiang@...>
Date: 2018-04-15T15:12:16Z
fix type coercion when promting to StringType
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