> ## Documentation Index
> Fetch the complete documentation index at: https://docs.regatta.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Hint - Cardinality

### Synopsis

`CARDINALITY (object_name, number)`

A hint to specify the expected record set size in a specific operation.

`OBJECT_NAME` can be:

1. A specific table. Contains the expected number of rows in the table. For example:

```sql theme={null}
SELECT /*++ CARDINALITY (o, 100) */ s.name, o.id
FROM staff s JOIN org o
ON s.deptno = o.deptno
WHERE o.division = 'EASTERN';
```

Here the hint indicates that there are 100 rows in the `org` table (for the purpose of query optimization). It doesn’t say anything about how many of them have `division = ’EASTERN’.`

2. An alias given to a sub-query result. Contains the expected results from it as if it was done **without push down/up**. The sub-query must be aliased, and the alias name passed as the argument of the hint.

For example:

```sql theme={null}
SELECT /*++ CARDINALITY (east_deptnumb, 10000) */
s.name, east_deptnumb.id
FROM staff s JOIN (SELECT o.deptno ,id
                   FROM org o
                   WHERE o.division = 'EASTERN') AS east_deptnumb
ON s.deptno = east_deptnumb.deptno;
```

Specifying multiple hints with the same **object\_name** and different numbers is contradictory and is not allowed.