# 1907. Count Salary Categories

## Description

Table: Accounts

+-------------+------+
| Column Name | Type |
+-------------+------+
| account_id  | int  |
| income      | int  |
+-------------+------+
account_id is the primary key (column with unique values) for this table.
Each row contains information about the monthly income for one bank account.


Write a solution to calculate the number of bank accounts for each salary category. The salary categories are:

• "Low Salary": All the salaries strictly less than $20000. • "Average Salary": All the salaries in the inclusive range [$20000, $50000]. • "High Salary": All the salaries strictly greater than $50000.

The result table must contain all three categories. If there are no accounts in a category, return 0.

Return the result table in any order.

The result format is in the following example.

Example 1:

Input:
Accounts table:
+------------+--------+
| account_id | income |
+------------+--------+
| 3          | 108939 |
| 2          | 12747  |
| 8          | 87709  |
| 6          | 91796  |
+------------+--------+
Output:
+----------------+----------------+
| category       | accounts_count |
+----------------+----------------+
| Low Salary     | 1              |
| Average Salary | 0              |
| High Salary    | 3              |
+----------------+----------------+
Explanation:
Low Salary: Account 2.
Average Salary: No accounts.
High Salary: Accounts 3, 6, and 8.


## Solutions

Solution 1: Temporary Table + Grouping + Left Join

We can first create a temporary table containing all salary categories, and then count the number of bank accounts for each salary category. Finally, we use a left join to connect the temporary table with the result table to ensure that the result table contains all salary categories.

Solution 2: Filtering + Merging

We can filter out the number of bank accounts for each salary category separately, and then merge the results. Here, we use UNION to merge the results.

• # Write your MySQL query statement below
WITH
S AS (
SELECT 'Low Salary' AS category
UNION
SELECT 'Average Salary'
UNION
SELECT 'High Salary'
),
T AS (
SELECT
CASE
WHEN income < 20000 THEN "Low Salary"
WHEN income > 50000 THEN 'High Salary'
ELSE 'Average Salary'
END AS category,
COUNT(1) AS accounts_count
FROM Accounts
GROUP BY 1
)
SELECT category, IFNULL(accounts_count, 0) AS accounts_count
FROM
S
LEFT JOIN T USING (category);