What are the limitations of Query Entity?

This may helps you

docs.appian.com/.../Post-Install_Configurations.html

docs.appian.com/.../Configuring_Relational_Databases.html

Along with Mangesh inputs, do consider database performance best pracitices also,
community.appian.com/.../database-performance-best-practices

Hello,
You can find out the details for query Entity in the documentation. One thing I want to tell about query entity is by default the query entity sort the result on the basis of the first selected column.

For example:-
If you are not defining any sort field with query Entity:-
a!queryEntity(
entity: Entity Name
query: {
a!query(
selection:{
a!querySelection(
columns: {

a!queryColumn(
field: "columnA"
),
a!queryColumn(
field: "columnB"
)
}
)
},
pagingInfo: a!pagingInfo(
startIndex: 1,
batchSize: -1
)
)
}
)

The above query will give the result and the sorting of the result will be on the column :- columnA .

This may be not the exact answer you are looking for, but may be this will help you.

Thanks
Sahil Batra

One of the limitations I would vote on,
Aggregation functions always expects at least one field to be grouped, for example: you cannot simply get the MAX/MIN/AVG/COUNT on column level, it always has to be grouped by that column which returns distinct values rather than a single aggregated value.

Adding to what Smruti Swain said on Aggregation, when you use aggregation, sorting can be done only on fields that are selected.