[LeetCode] Count Salary Categories

https://leetcode.com/problems/count-salary-categories/description/

Union All을 잊지 말자. 그리고, select에 ''를 걸어 아예 필요한 문자열을 추출해버릴 수 있더라.

WITH COUNT_SAL AS(
    SELECT
        'Low Salary' AS 'category',
        COUNT(*) AS 'accounts_count'
    FROM
        ACCOUNTS
    WHERE INCOME < 20000

    UNION ALL

    SELECT
        'Average Salary' AS 'category',
        COUNT(*) AS 'accounts_count'
    FROM
        ACCOUNTS
    WHERE INCOME BETWEEN 20000 AND 50000

    UNION ALL

    SELECT
        'High Salary' AS 'category',
        COUNT(*) AS 'accounts_count'
    FROM
        ACCOUNTS
    WHERE INCOME > 50000
)

SELECT
    category,
    CASE WHEN accounts_count is null then 0 else accounts_count END as accounts_count
FROM COUNT_SAL