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Summary

fix distinct set-returning function

for example

root@0.0.0.0:48000/default> select distinct unnest(split(coalesce(NULL, 'a,b,a,b,c'), ',')) as c1;
┌──────────────────┐
│        c1        │
│ Nullable(String) │
├──────────────────┤
│ a                │
│ b                │
│ c                │
└──────────────────┘
3 rows read in 0.117 sec. Processed 1 rows, 1 B (8.55 rows/s, 8 B/s)

• fixes: bug: Unnest still does not work for some cases #16873

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

This change is