In Postgres, we can use the STRING_AGG() function to transform our query results into a comma separated list.
Instead of each value being output in a separate row (as with any regular query), the values are output to a single row, separated by a comma (or some other delimiter of our choosing).
MySQL has a GROUP_CONCAT() function that enables us to return columns from a query as a delimited list.
It returns a string result with the concatenated non-NULL values from a group.
In Oracle, the LISTAGG() function enables us to combine data from multiple rows in to a single row.
We have the option of specifying a separator (such as a comma). We can also order the results produced by the LISTAGG() function, and more.
MariaDB has a GROUP_CONCAT() function that enables us to return columns from a query as a delimited list.
In PostgreSQL, we can use the STRING_AGG() function to return columns from a query as a delimited list.
In MongoDB, the $unionWith aggregation pipeline stage performs a union of two collections, and it includes duplicates.
This behaves in a similar way to SQL’s UNION ALL, which also includes duplicates. By contrast, using just UNION (i.e. without the ALL)in SQL removes duplicates.
In MongoDB, we don’t have the option of specifying $unionWith ALL or similar, so we need to reduce duplicates in another way.
In MongoDB, we can remove duplicates by using the $group stage.
This article lists the various aggregation pipeline operators that can be used to return individual date parts from a Date object in MongoDB.
MongoDB includes the $strLenBytes and $strLenCP operators in its aggregation pipeline framework. These operators do a similar but slightly different thing. In some cases, both will return exactly the same result, while in other cases the results will differ.
Here’s a quick overview of the difference between these two operators.
If you need to return the size of a document in MongoDB, you can use the following:
$bsonSize aggregation pipeline operatorObject.bsonSize() methodBelow are examples of each approach.