[GitHub] hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a union of CHAR columns of different lengths should be VARCHAR

2018-08-28 Thread GitBox 
hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a 
union of CHAR columns of different lengths should be VARCHAR
URL: https://github.com/apache/flink/pull/6519#issuecomment-416501305
 
 
   @pnowojski  Thanks for looking into it.
I think there are bugs in all your 4 sqls, so we can't get the conclusions 
from them.
   - In mysql, trailing spaces are removed when CHAR values are retrieved from 
a table. 
   - You use literal of length 3('aa ') to compare to CHAR(4) and VARCHAR(4).
   - Except for mysql, other database will not remove trailing spaces so that 
the result of `case when` contains blanks.
   
   What result type of `case when`? Should we change case when result type to 
varchar? I think we can get the answer form the following sqls.
   1. Mysql
   There are no doubt, since mysql Reference Manual says the return type is 
VARCHAR.
   
   2. Oracle
   [http://sqlfiddle.com/#!4/cd577/2/0](http://sqlfiddle.com/#!4/cd577/2/0)
   
   3. PostgreSql
   [http://sqlfiddle.com/#!17/c20bd/3/0](http://sqlfiddle.com/#!17/c20bd/3/0)
   
   4. SqlServer
   [http://sqlfiddle.com/#!18/c20bd/10/0](http://sqlfiddle.com/#!18/c20bd/10/0)
   
   From the results, we can see that
   - There are no trailing spaces 
   - The result type length should not be 1, i.e., can not be char(1) or 
varchar(1). It should be char(3) or varchar(3)
   - Result of `concat(CAST('a' AS char(3)), '|')` contains blanks while 
`concat(CAST('a' AS varchar(3)), '|')`  not, so the result type of `case when` 
should be varchar.
   
   In Calcite, character constant, for example 'Hello, world!', '', 
_N'Bonjour', _ISO-8859-1'It''s superman!' COLLATE SHIFT_JIS$ja_JP$2. These are 
always CHAR, never VARCHAR. So it seems not possible or acceptable to change 
all literals to VARCHAR in Calcite.
   I think it is meaningful to turn the result type of `case when` to VARCHAR. 
What do you think?
   
   Thanks, Hequn
   


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[GitHub] hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a union of CHAR columns of different lengths should be VARCHAR

2018-08-24 Thread GitBox 
hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a 
union of CHAR columns of different lengths should be VARCHAR
URL: https://github.com/apache/flink/pull/6519#issuecomment-415735866
 
 
   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---'.  BTW, '-' means the blank.
   
   It is true the sql standard returns CHAR type, but nearly all major DBMSs 
return VARCHAR without blank-padded. A tool for easy online testing: 
http://sqlfiddle.com/
   
   Thanks, Hequn
   


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[GitHub] hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a union of CHAR columns of different lengths should be VARCHAR

2018-08-24 Thread GitBox 
hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a 
union of CHAR columns of different lengths should be VARCHAR
URL: https://github.com/apache/flink/pull/6519#issuecomment-415735866
 
 
   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---'.  BTW, '-' means the blank.
   
   It is true the sql standard returns CHAR type, but nearly all major DBMSs 
return VARCHAR without blank-padded.
   
   Thanks, Hequn
   


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