strongduanmu commented on issue #10563:
URL:
https://github.com/apache/shardingsphere/issues/10563#issuecomment-851383186
After we change the sql to `select count(1) from t_order group by order_id
order by order_id desc;`, another error will occur:
```
ERROR: Can't find index: AggregationProjection(type=COUNT,
innerExpression=(1), alias=Optional.empty, derivedAggregationProjections=[],
index=-1), please add alias for aggregate selections
```
This exception is because the `columnLabel` that in the
`columnLabelIndexMap` returned by PG is `count`, and the `columnLabel`
processed by SS is `count(1)`, the inconsistency of the `columnLabel` results
in an exception in the verification. Considering the different processing way
of MySQL, we need to distinguish between different database dialects to obtain
the `columnLabel` in SS.
```java
private void setIndexForAggregationProjection(final Map<String, Integer>
columnLabelIndexMap) {
for (AggregationProjection each :
projectionsContext.getAggregationProjections()) {
Preconditions.checkState(columnLabelIndexMap.containsKey(each.getColumnLabel()),
"Can't find index: %s, please add alias for aggregate selections", each);
each.setIndex(columnLabelIndexMap.get(each.getColumnLabel()));
for (AggregationProjection derived :
each.getDerivedAggregationProjections()) {
Preconditions.checkState(columnLabelIndexMap.containsKey(derived.getColumnLabel()),
"Can't find index: %s", derived);
derived.setIndex(columnLabelIndexMap.get(derived.getColumnLabel()));
}
}
}
```
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