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1729. Find Followers Count.sql

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-- Problem

-- +-------------+------+

-- | Column Name | Type |

-- +-------------+------+

-- | user_id | int |

-- | follower_id | int |

-- +-------------+------+

-- (user_id, follower_id) is the primary key (combination of columns with unique values) for this table.

-- This table contains the IDs of a user and a follower in a social media app where the follower follows the user.

-- Write a solution that will, for each user, return the number of followers.

-- Return the result table ordered by user_id in ascending order.

-- The result format is in the following example.

-- Example 1:

-- Input:

-- Followers table:

-- +---------+-------------+

-- | user_id | follower_id |

-- +---------+-------------+

-- | 0 | 1 |

-- | 1 | 0 |

-- | 2 | 0 |

-- | 2 | 1 |

-- +---------+-------------+

-- Output:

-- +---------+----------------+

-- | user_id | followers_count|

-- +---------+----------------+

-- | 0 | 1 |

-- | 1 | 1 |

-- | 2 | 2 |

-- +---------+----------------+

-- Explanation:

-- The followers of 0 are {1}

-- The followers of 1 are {0}

-- The followers of 2 are {0,1}

-- Solution

select user_id, count(follower_id) followers_count

from Followers

group by user_id

order by user_id;