2. [MySQL] 평균 구하기

    테이블과 결과

    Input: 
Signups table:
+---------+---------------------+
| user_id | time_stamp          |
+---------+---------------------+
| 3       | 2020-03-21 10:16:13 |
| 7       | 2020-01-04 13:57:59 |
| 2       | 2020-07-29 23:09:44 |
| 6       | 2020-12-09 10:39:37 |
+---------+---------------------+
Confirmations table:
+---------+---------------------+-----------+
| user_id | time_stamp          | action    |
+---------+---------------------+-----------+
| 3       | 2021-01-06 03:30 …
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  3. [MySQL] REGEXP_LIKE

    테이블과 결과

    Input: 
Patients table:
+------------+--------------+--------------+
| patient_id | patient_name | conditions   |
+------------+--------------+--------------+
| 1          | Daniel       | YFEV COUGH   |
| 2          | Alice        |              |
| 3          | Bob          | DIAB100 MYOP |
| 4          | George       | ACNE DIAB100 |
| 5          | Alain        | DIAB201      |
+------------+--------------+--------------+
Output: 
+------------+--------------+--------------+
| patient_id | patient_name | conditions   |
+------------+--------------+--------------+
| 3          | Bob          | DIAB100 MYOP |
| 4          | George       | ACNE DIAB100 | 
+------------+--------------+--------------+
Explanation: Bob and George both have a condition that …
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  5. [MySQL] SELECT 존재여부 체크

    SELECT 존재여부 체크

    • COUNT(*)로 세는 것이 더 느릴 수 있다. 그냥 1로 해라
    SELECT EXISTS 
(
    SELECT 1
    FROM CVVE_POINT.CPO_POINT_EARN cpe, CVVE_CUSTOMER.CR_CUSTOMER cc
    WHERE cpe.CR_ID = cc.CR_ID
    AND cpe.CUH_ID = cc.CUH_ID
    AND cpe.CPE_ISSUE_DT BETWEEN DATE_ADD …
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  6. [MySQL] SELF JOIN

    테이블

    Employee 테이블

    id name salary managerId
    1 Joe 70000 3
    2 Henry 80000 4
    3 Sam 60000
    4 Max 90000

    문제

    • 자신의 매니저보다 많이 salary를 받는 인원을 뽑으시오

    답

    SELECT e1 …
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  8. [MySQL] 실행계획

    실행계획

    • id: select id
    • select_type: SIMPLE, UNION, SUBQUERY, etc
    • type: data scan type (const, ALL, ref, range, index, fulltext, etc)
    • const: 클러스터드 인덱스, 유니크 인덱스를 사용했을 때
    • ALL: 인덱스를 타 …
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