hanyuzheng7 opened a new pull request, #23175:
URL: https://github.com/apache/flink/pull/23175
## What is the purpose of the change
Implement the elt function to extract the n-th input value from a row of
inputs.
The elt function in the ETL pipeline extracts the value at the n-th position
from a input row. It is similar to array indexing, where the first element is
at position 1. This function provides a convenient way to retrieve specific
elements from a row of inputs.
## Brief change log
ELT for Table API and SQL
## Verifying this change
Syntax:
`ELT(row, n)`
Arguments:
row: input row, it can contain mixed type data.
n: The index of the input value to extract. It should be a positive integer.
Returns: Returns the element at the n-th position from a row of input
values. If 'n' is less than 1 or greater than the number of inputs, or if any
of the inputs is null, the function will return null.
Examples:
```
SELECT ELT(('scala', 'java'), 2)
Output: 'java'
SELECT ELT((2, 'a'), 1)
Output: 2
```
See also:
spark:https://spark.apache.org/docs/latest/api/sql/index.html#elt
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): (yes / no)
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: (yes / no)
- The serializers: (yes / no / don't know)
- The runtime per-record code paths (performance sensitive): (yes / no /
don't know)
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
- The S3 file system connector: (yes / no / don't know)
## Documentation
- Does this pull request introduce a new feature? (yes / no)
- If yes, how is the feature documented? (not applicable / docs / JavaDocs
/ not documented)
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