Hi @pnowojski , thanks for your reply. There are many cases need this feature.
Not only `case when`, but also `nvl`, `greatest` and `least`. Most users
encounter the blank problem is `case when`. Examples have been added in the
test cases. Below I will add some more examples:
1.
```
SELECT country_name
FROM (
SELECT CASE id
WHEN 1 THEN 'GERMANY'
WHEN 2 THEN 'CANADA'
ELSE 'INVALID COUNTRY ID'
END AS country_name
FROM country_id
)
WHERE country_name = 'GERMANY'
```
This sql will output nothing since the blank problem. It is very confused.
2.
```
SELECT country_name, country_info
FROM (
SELECT CASE id
WHEN 1 THEN 'GERMANY'
WHEN 2 THEN 'CANADA'
ELSE 'INVALID COUNTRY ID'
END AS country_name
FROM country_id
) nameTable join infoTable on nameTable.country_name = infoTable.country_name;
```
This sql cannot join correctly since the blank problem. 'GERMANY' in nameTable
becomes 'GERMANY '.
It is true the sql standard returns CHAR type, but nearly all major DBMSs
return VARCHAR without blank-padded.
Thanks, Hequn
[ Full content available at: https://github.com/apache/flink/pull/6519 ]
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