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https://issues.apache.org/jira/browse/FLINK-21563?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17294237#comment-17294237
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Jark Wu commented on FLINK-21563:
---------------------------------
Not sure how SQL standard and other database vendors handle this. I just
checked MySQL, and it supports this.
{code}
mysql> CREATE TABLE triangle (
-> sidea DOUBLE,
-> sideb DOUBLE,
-> sidec DOUBLE AS (SQRT(sidea * sidea + sideb * sideb)),
-> sided DOUBLE AS (sidec+1)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> INSERT INTO triangle (sidea, sideb) VALUES(1,1),(3,4),(6,8);
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from triangle;
+-------+-------+--------------------+-------------------+
| sidea | sideb | sidec | sided |
+-------+-------+--------------------+-------------------+
| 1 | 1 | 1.4142135623730951 | 2.414213562373095 |
| 3 | 4 | 5 | 6 |
| 6 | 8 | 10 | 11 |
+-------+-------+--------------------+-------------------+
3 rows in set (0.00 sec)
{code}
> Support using computed columns when defining new computed columns
> -----------------------------------------------------------------
>
> Key: FLINK-21563
> URL: https://issues.apache.org/jira/browse/FLINK-21563
> Project: Flink
> Issue Type: New Feature
> Components: Table SQL / API
> Affects Versions: 1.11.3
> Reporter: Nico Kruber
> Priority: Major
> Attachments: flights-21563.csv
>
>
> To avoid code duplications, it would be nice to be able to use computed
> columns in later computations of new computed columns, e.g.
> {code}
> CREATE TABLE `flights` (
> `_YEAR` CHAR(4),
> `_MONTH` CHAR(2),
> `_DAY` CHAR(2),
> `_SCHEDULED_DEPARTURE` CHAR(4),
> `SCHEDULED_DEPARTURE` AS TO_TIMESTAMP(`_YEAR` || '-' || `_MONTH` || '-' ||
> `_DAY` || ' ' || SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 0 FOR 2) || ':' ||
> SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 3) || ':00'),
> `_DEPARTURE_TIME` CHAR(4),
> `DEPARTURE_DELAY` SMALLINT,
> `DEPARTURE_TIME` AS TIMESTAMPADD(MINUTE, CAST(`DEPARTURE_DELAY` AS INT),
> SCHEDULED_DEPARTURE)
> )...
> {code}
> Otherwise, a user would have to repeat these calculations over and over again
> which is not that maintainable.
> Currently, for a minimal working example with the attached input file, it
> would look like this, e.g. in the SQL CLI:
> {code}
> CREATE TABLE `flights` (
> `_YEAR` CHAR(4),
> `_MONTH` CHAR(2),
> `_DAY` CHAR(2),
> `_SCHEDULED_DEPARTURE` CHAR(4),
> `SCHEDULED_DEPARTURE` AS TO_TIMESTAMP(`_YEAR` || '-' || `_MONTH` || '-' ||
> `_DAY` || ' ' || SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 0 FOR 2) || ':' ||
> SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 3) || ':00'),
> `_DEPARTURE_TIME` CHAR(4),
> `DEPARTURE_DELAY` SMALLINT,
> `DEPARTURE_TIME` AS TIMESTAMPADD(MINUTE, CAST(`DEPARTURE_DELAY` AS INT),
> TO_TIMESTAMP(`_YEAR` || '-' || `_MONTH` || '-' || `_DAY` || ' ' ||
> SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 0 FOR 2) || ':' ||
> SUBSTRING(`_SCHEDULED_DEPARTURE` FROM 3) || ':00'))
> ) WITH (
> 'connector' = 'filesystem',
> 'path' = 'file:///tmp/kaggle-flight-delay/flights-21563.csv',
> 'format' = 'csv'
> );
> SELECT * FROM flights;
> {code}
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