Issue type:

[x] question
[ ] bug report
[ ] feature request
[x] documentation issue

Database system/driver:

[ ] cordova
[x] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[ ] postgres
[ ] cockroachdb
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[x] latest
[ ] @next
[ ] 0.x.x (or put your version here)

In PostgreSQL, @ is a unary operator that returns the absolute value of a number. For example:

jordan=# select @ -5.0;
 ?column?
----------
      5.0
(1 row)

CockroachDB is missing such a unary operator.