hanyuzheng7 opened a new pull request, #23194:
URL: https://github.com/apache/flink/pull/23194
### What is the purpose of the change
This is an implementation of HISTOGRAM
Returns a map containing the distinct values of col1 mapped to the number of
times each one occurs for the given window. This version limits the number of
distinct values which can be counted to 1000, beyond which any additional
entries are ignored.
### Brief change log
HISTOGRAM for Table API and SQL
Syntax:
`HISTOGRAM(col1)
`
Arguments:
col1: the data in col1
Examples:
```
Flink SQL> create temporary table orders (
> orderId INT,
> price DECIMAL(10,3)
> )with(
> 'connector' = 'datagen',
> 'rows-per-second' = '5',
> 'fields.orderId.min' = '1',
> 'fields.orderId.max' = '20',
> 'fields.price.min' = '1',
> 'fields.price.max' = '200'
> );
```
`Flink SQL> select histogram(price) as map from orders;`
`res: {147.451 = 1， 65.765 = 1， 41.662 = 1 …}`
see also:
KsqlDB:
https://docs.ksqldb.io/en/latest/developer-guide/ksqldb-reference/aggregate-functions/#histogram
### Verifying this change
- This change added tests in CollectionFunctionsITCase.
### Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): (no)
- The public API, i.e., is any changed class annotated with
@Public(Evolving): (yes)
- The serializers: (no)
- The runtime per-record code paths (performance sensitive): (no)
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
- The S3 file system connector: (no)
### Documentation
- Does this pull request introduce a new feature? (yes)
- If yes, how is the feature documented? (docs)
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