morrySnow opened a new pull request, #61813:
URL: https://github.com/apache/doris/pull/61813
### What problem does this PR solve?
Issue Number: close #xxx
Problem Summary:
When parsing a simple CASE expression with a subquery as the value
(e.g., `CASE (SELECT sum(col) FROM t) WHEN 1 THEN 2 WHEN 3 THEN 4 END`),
the parser (`LogicalPlanBuilder.visitSimpleCase`) duplicated the same
subquery
expression into multiple `EqualTo` nodes across WhenClauses. Since the
subquery
carried a fixed `RelationId`, this created duplicate RelationIds in the plan
tree.
Later, different SlotIds were assigned to the same `SlotReference` in
different
copies, preventing them from being merged back into one subquery. This caused
the **"groupExpression already exists in memo"** error.
**How to reproduce:**
```sql
CREATE TABLE test (
big_key int,
int_1 int
) PROPERTIES (
"replication_allocation" = "tag.location.default: 1"
);
select case (select sum(int_1) from test)
when 1 then 2
when 3 then 4
else 5
end a3 from test;
-- Error: groupExpression already exists in memo, maybe a bug
```
**Solution:**
The fix defers `EqualTo` construction from parse time to analysis time:
1. Added a `value` field to `CaseWhen` expression, stored as `children[0]`
when present. Children layout: `[value?, WhenClause+, defaultValue?]`
2. `LogicalPlanBuilder.visitSimpleCase` now passes the value to `CaseWhen`
directly instead of wrapping each WhenClause operand in `EqualTo(value,
operand)`
3. `ExpressionAnalyzer.visitCaseWhen` handles simple case: analyzes the
value once, then constructs `EqualTo(analyzedValue, analyzedOperand)` per
WhenClause with proper type coercion via
`TypeCoercionUtils.processComparisonPredicate`, producing a standard
searched-case `CaseWhen` (no value field). This ensures the subquery is
analyzed exactly once with a single `RelationId`.
After analysis, all downstream rules see a standard searched-case `CaseWhen`
— no changes needed elsewhere.
### Release note
Fixed a bug where using a scalar subquery as the value in a simple CASE
expression (e.g., `CASE (SELECT ...) WHEN val THEN ...`) caused a
"groupExpression already exists in memo" planning error.
### Check List (For Author)
- Test: Unit Test (CaseWhenTest - 7 tests) / Regression Test
(test_subquery_in_simple_case - 7 cases)
- Behavior changed: No
- Does this need documentation: No
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