whitecloud6688 opened a new pull request, #19442:
URL: https://github.com/apache/flink/pull/19442
## What is the purpose of the change
请支持类似以下语法：
select if(1>2,1,NULL) as col1;
select NULL as col1;
## Brief change log
需要将 NULL 赋值给一个字段，然后写入表，但报语法错误。版本：FLINK-1.13.6。
Flink SQL> select if(1>2,1,NULL) as col1;
[ERROR] Could not execute SQL statement. Reason:
org.apache.calcite.sql.validate.SqlValidatorException: Illegal use of 'NULL'
Flink SQL> select NULL as col1;
[ERROR] Could not execute SQL statement. Reason:
org.apache.calcite.sql.validate.SqlValidatorException: Illegal use of 'NULL'
以下语法能执行
Flink SQL> select NULL is NULL as col1;
+----+--------+
| op | col1 |
+----+--------+
| +I | true |
+----+--------+
Received a total of 1 row
## Verifying this change
select if(1>2,1,NULL) as col1;
select NULL as col1;
## 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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