> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/1949-strong-friendship.md).

# 1949. Strong Friendship

<https://leetcode.com/problems/strong-friendship>

## Description

Table: `Friendship`

```
+-------------+------+
| Column Name | Type |
+-------------+------+
| user1\_id    | int  |
| user2\_id    | int  |
+-------------+------+
(user1\_id, user2\_id) is the primary key for this table.
Each row of this table indicates that the users user1\_id and user2\_id are friends.
Note that user1\_id < user2\_id.
```

A friendship between a pair of friends `x` and `y` is **strong** if `x` and `y` have **at least three** common friends.

Write an SQL query to find all the **strong friendships**.

Note that the result table should not contain duplicates with `user1_id < user2_id`.

Return the result table in **any order**.

The query result format is in the following example:

```
Friendship table:
+----------+----------+
| user1\_id | user2\_id |
+----------+----------+
| 1        | 2        |
| 1        | 3        |
| 2        | 3        |
| 1        | 4        |
| 2        | 4        |
| 1        | 5        |
| 2        | 5        |
| 1        | 7        |
| 3        | 7        |
| 1        | 6        |
| 3        | 6        |
| 2        | 6        |
+----------+----------+
Result table:
+----------+----------+---------------+
| user1\_id | user2\_id | common\_friend |
+----------+----------+---------------+
| 1        | 2        | 4             |
| 1        | 3        | 3             |
+----------+----------+---------------+
Users 1 and 2 have 4 common friends (3, 4, 5, and 6).
Users 1 and 3 have 3 common friends (2, 6, and 7).
We did not include the friendship of users 2 and 3 because they only have two common friends (1 and 6).
```

## ac

```java
```