[SQL/코드카타] 유저별 confirmed 의 비율 ( 평균이 바로 비율 )

문제 더보기Table: Signups+----------------+----------+| Column Name | Type |+----------------+----------+| user_id | int || time_stamp | datetime |+----------------+----------+user_id is the column of unique values for this table.Each row contains information about the signup time for the user with ID user_id. Table: Confirmations+----------------+----------+| Column Name | ..

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• · 2025. 11. 21.
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[SQL/코드카타] 직속 하위 직원이 5명 이상인 매니저 찾기

문제 더보기Table: Employee+-------------+---------+| Column Name | Type |+-------------+---------+| id | int || name | varchar || department | varchar || managerId | int |+-------------+---------+id is the primary key (column with unique values) for this table.Each row of this table indicates the name of an employee, their department, and the id of their manager.If manag..

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• · 2025. 11. 19.
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[SQL/코드카타] 모든 조합의 CROSS JOIN과 참여한 시험을 LEFT JOIN

문제 더보기Table: Students+---------------+---------+| Column Name | Type |+---------------+---------+| student_id | int || student_name | varchar |+---------------+---------+student_id is the primary key (column with unique values) for this table.Each row of this table contains the ID and the name of one student in the school. Table: Subjects+--------------+---------+| Column Name | Ty..

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• · 2025. 11. 18.
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[SQL/코드카타] WHERE 조건절과 NULL값 출력

문제 87번 더보기Table: Employee+-------------+---------+| Column Name | Type |+-------------+---------+| empId | int || name | varchar || supervisor | int || salary | int |+-------------+---------+empId is the column with unique values for this table.Each row of this table indicates the name and the ID of an employee in addition to their salary and the id of their man..

• format_list_bulleted SQL
• · 2025. 11. 17.
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[SQL/코드카타] Average Time of Process per Machine

문제Table: Activity더보기+----------------+---------+| Column Name | Type |+----------------+---------+| machine_id | int || process_id | int || activity_type | enum || timestamp | float |+----------------+---------+The table shows the user activities for a factory website.(machine_id, process_id, activity_type) is the primary key (combination of columns with unique v..

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• · 2025. 11. 14.
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[SQLD] 기출로 본 2과목 핵심 개념

1. 출력값은?START WITH COL3 = 4CONNECT BY COL1 = FRIOR COL2;➡️ START WITH 절부터 시작하고, 그 다음 CONNECT BY 절을 따라감전행의 COL2와 현행의 COL1 이 같아야 한다는 뜻 2. 다른 것은?(인수1, 인수2)일때IFNULL(NULL, 'A') : 인수1이 NULL 일 때, 인수2 반환(mysql버전)NVL(NULL, 'A') : 인수1이 NULL 일 때, 인수2 반환(oracle버전)COALESCE(NULL, 'A') : NULL이 아닌 최초의 인수를 반환 (인수1, 인수2, 인수3, 인수4 ,,,,,, ) NULLIF(NULL, 'A') : 인수1과 인수2가 같으면 NULL, 같지 않으면 인수1을 반환 (null 반환하지만 실제론 에러발..

• format_list_bulleted 자격증/SQLD
• · 2025. 11. 13.
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