luchunliang opened a new issue, #12213:
URL: https://github.com/apache/inlong/issues/12213
### Description
This feature adds first-class support for the SQL `NULL` literal in
Transform SDK expressions.
Previously, a `SELECT` expression that used `NULL` directly (e.g.
`ifnull(null, 3)`, `coalesce(null, col)`) failed during parser construction:
```
java.lang.ClassCastException: net.sf.jsqlparser.expression.NullValue cannot
be cast to net.sf.jsqlparser.schema.Column
at
org.apache.inlong.sdk.transform.process.parser.ParserTools.getTransformParser(ParserTools.java:72)
at
org.apache.inlong.sdk.transform.process.operator.OperatorTools.buildParser(OperatorTools.java:119)
at
org.apache.inlong.sdk.transform.process.function.condition.IfNullFunction.<init>(IfNullFunction.java:57)
```
With this feature, the `NULL` literal is resolved to a constant Java `null`,
enabling `ifnull(null, x)` / `coalesce(null, x)` / `concat_ws(..., null, ...)`
and similar expressions to work as expected.
### Use case
### Component
`inlong-sdk / transform-sdk`
- `org.apache.inlong.sdk.transform.process.parser.NullValueParser` *(new)*
- Test:
`org.apache.inlong.sdk.transform.process.function.condition.TestIfNullFunction`
### Description
This feature adds first-class support for the SQL `NULL` literal in
Transform SDK expressions.
Previously, a `SELECT` expression that used `NULL` directly (e.g.
`ifnull(null, 3)`, `coalesce(null, col)`) failed during parser construction:
```
java.lang.ClassCastException: net.sf.jsqlparser.expression.NullValue cannot
be cast to net.sf.jsqlparser.schema.Column
at
org.apache.inlong.sdk.transform.process.parser.ParserTools.getTransformParser(ParserTools.java:72)
at
org.apache.inlong.sdk.transform.process.operator.OperatorTools.buildParser(OperatorTools.java:119)
at
org.apache.inlong.sdk.transform.process.function.condition.IfNullFunction.<init>(IfNullFunction.java:57)
```
With this feature, the `NULL` literal is resolved to a constant Java `null`,
enabling `ifnull(null, x)` / `coalesce(null, x)` / `concat_ws(..., null, ...)`
and similar expressions to work as expected.
### Background
`ParserTools.getTransformParser(Expression expr)` resolves parsers through a
reflective scan that maps `Expression` sub-types to their parser classes
(`parserMap`). Expression types that are not registered currently fall back to
a `Column` cast:
```java
Class<?> clazz = parserMap.get(expr.getClass());
if (clazz == null) {
return new ColumnParser((Column) expr); // NULL literal hits here and
crashes
}
```
The SQL `NULL` literal is parsed by JSqlParser as
`net.sf.jsqlparser.expression.NullValue`, which is not a `Column`. Because no
parser was registered for it, any `NULL` literal hit the fallback branch and
raised a `ClassCastException`.
### Proposed Change
Introduce a `NullValueParser` following the existing `StringParser` pattern:
```java
@TransformParser(values = NullValue.class)
public class NullValueParser implements ValueParser {
public NullValueParser(NullValue expr) {
// The NULL literal carries no value; nothing to store.
}
@Override
public Object parse(SourceData sourceData, int rowIndex, Context
context) {
return null;
}
}
```
`@TransformParser(values = NullValue.class)` registers `NullValue.class` in
`parserMap`, so `getTransformParser` resolves it through the reflective
constructor branch, and `NULL` literals evaluate to constant `null`.
### Resulting Behavior
- `ifnull(null, numeric2)` evaluates its first argument to `null`, so
`IfNullFunction` falls back to the second argument as expected.
- Other functions that receive a `NULL` literal as an argument (e.g.
`coalesce`, `num_nulls`, `concat_ws`) no longer fail during parser construction.
### Tests
Added a true-`NULL`-literal case to `TestIfNullFunction`:
```java
// case6: ifnull(null, numeric2) -- true NULL literal
transformSql = "select ifnull(null,numeric2) from source";
data = "5|3|3|5";
Assert.assertEquals("result=3", output.get(0));
```
Verified: `Tests run: 1, Failures: 0, Errors: 0, Skipped: 0`.
### Backward Compatibility
- Fully backward compatible.
- No public API or method-signature change; only a new parser class is added.
- Existing column / function / literal parsers are unaffected.
### Files Changed
-
`inlong-sdk/transform-sdk/src/main/java/org/apache/inlong/sdk/transform/process/parser/NullValueParser.java`
*(new)*
-
`inlong-sdk/transform-sdk/src/test/java/org/apache/inlong/sdk/transform/process/function/condition/TestIfNullFunction.java`
### Are you willing to submit PR?
- [x] Yes, I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://www.apache.org/foundation/policies/conduct)
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