[I] [FLINK] Bug: VARCHAR literal value includes charset prefix `_UTF-16LE'...'` in output [gluten]

["ggjh-159 (via GitHub)" <gi...@apache.org>]

ggjh-159 opened a new issue, #12249:
URL: https://github.com/apache/gluten/issues/12249

   ### Backend
   
   VL (Velox)
   
   ### Bug description
   
   # Bug: VARCHAR literal value includes charset prefix `_UTF-16LE'...'` in output
   
   ## Problem
   
   When a SQL query contains VARCHAR string literals (e.g., `CASE WHEN ... THEN 'nightTime'`), the
   output produced by Gluten-Flink includes an unexpected charset prefix `_UTF-16LE'...'` around the
   string value. For example, `'nightTime'` is rendered as `_UTF-16LE'nightTime'` in the Print
   connector output.
   
   Native Flink (without Gluten) outputs the correct plain string value `nightTime`.
   
   ## Root Cause
   
   In `RexNodeConverter.toVariant()`, the VARCHAR branch calls `literal.getValue().toString()`. For
   VARCHAR type, `RexLiteral.getValue()` returns a Calcite `NlsString` object. `NlsString.toString()`
   produces the SQL literal format with charset prefix: `_UTF-16LE'value'`, not the raw string value.
   
   The CHAR branch in the same method uses the correct API: `literal.getValueAs(String.class)`, which
   returns the plain string value.
   
   ## File
   
   - `gluten-flink/planner/src/main/java/org/apache/gluten/rexnode/RexNodeConverter.java`, line 113
   
   ## Verification: Native Flink does NOT have this issue
   
   Tested the same q14 query on native Flink (without Gluten JARs), the output is correct with no
   charset prefix:
   
   ```
   +I[1000, 2001, 26353920.936, nightTime, 2026-06-05T05:55:55.858, ..., 0]
   ```
   
   This confirms the `_UTF-16LE` prefix is introduced by Gluten's planner, not by Flink itself.
   
   ## Reproduce
   
   Run any nexmark query with VARCHAR string literals in CASE WHEN expressions, e.g., nexmark q14:
   
   ```sql
   SELECT
       auction, bidder, 0.908 * price as price,
       CASE
           WHEN HOUR(dateTime) >= 8 AND HOUR(dateTime) <= 18 THEN 'dayTime'
           WHEN HOUR(dateTime) <= 6 OR HOUR(dateTime) >= 20 THEN 'nightTime'
           ELSE 'otherTime'
       END AS bidTimeType,
       dateTime, extra,
       count_char(extra, 'c') AS c_counts
   FROM bid
   WHERE 0.908 * price > 1000000 AND 0.908 * price < 50000000
   ```
   
   ### Actual output (Gluten-Flink)
   
   ```
   +I[1012, 2001, 28428278.716, _UTF-16LE'nightTime', 2026-06-05T02:24:06.630, ..., 0]
   ```
   
   ### Expected output (native Flink)
   
   ```
   +I[1012, 2001, 28428278.716, nightTime, 2026-06-05T02:24:06.630, ..., 0]
   ```
   
   ## Environment
   
   - Gluten-Flink: 1.7.0-SNAPSHOT
   - Flink: 1.19.2
   
   ### Gluten version
   
   _No response_
   
   ### Spark version
   
   None
   
   ### Spark configurations
   
   _No response_
   
   ### System information
   
   _No response_
   
   ### Relevant logs
   
   ```bash
   
   ```


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Re: [I] [FLINK] Bug: VARCHAR literal value includes charset prefix `_UTF-16LE'...'` in output [gluten]

["ggjh-159 (via GitHub)" <gi...@apache.org>]

ggjh-159 closed issue #12249: [FLINK] Bug: VARCHAR literal value includes charset prefix `_UTF-16LE'...'` in output
URL: https://github.com/apache/gluten/issues/12249


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