gladydennyson opened a new issue, #38363:
URL: https://github.com/apache/shardingsphere/issues/38363
I am seeing an issue with arithmetic aggregate expressions of the form:
SUM(...) - SUM(...)
when the query runs across multiple shards.
### Example query pattern
```sql
SELECT
SUM(CASE
WHEN t.record_date = DATE '2025-04-02' THEN t.value_col
ELSE 0
END)
- SUM(CASE
WHEN t.record_date = DATE '2025-03-26' THEN t.value_col
ELSE 0
END) AS delta_value
FROM source_table t;
```
### Example numeric scenario
Suppose the query runs across two shards.
On shard 1, the expression `SUM(a) - SUM(b)` evaluates to `1681`.
On shard 2, the expression `SUM(a) - SUM(b)` evaluates to `420`.
### Expected result
2101 (1681 + 420)
### Actual result
Only one shard's value is returned 1681 .
### Environment
ShardingSphere version: 5.5.2
Database: PostgreSQL with TimescaleDB extension
Some tables involved are hypertables.
### Simplified sharding rule
Tables are distributed across two data sources:
ds_0
ds_1
Example configuration:
```yaml
source_table:
actualDataNodes: ds_${0..1}.source_table
```
Other tables used in joins follow the same distribution pattern.
### Question
Is there any limitation with cross-shard merging for expressions like
`SUM(...) - SUM(...)` that would explain why the final result is not matching
the expected result above?
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