重複記錄的出現，通常是用於程式後端驗證不嚴謹導致出現的垃圾資料，想要查詢並刪除，可通過以下實現方式

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查詢重複記錄

查詢指定欄位相同且總數大於一的資料

1. 先指明可能重複的欄位，可以是多個
2. 再根據分組查詢結果，通過 HAVING 進行判斷

SELECT 
	msan.memberSurvey_id, 
	msan.question_id, 
	msan.option_id 
FROM 
	pt_member_survey_answer msan 
GROUP BY 
	msan.memberSurvey_id, 
	msan.question_id, 
	msan.option_id 
HAVING
 
 
	COUNT(*) > 1

根據上述查詢結果將重複資料全部查出

1. 上述查詢會得到組合欄位中出現重複的情況
2. 根據該情況即可查詢出涉及到的具體資料條數

SELECT
	msa.*
FROM	
	pt_member_survey_answer msa
WHERE
	(msa.memberSurvey_id, msa.question_id, msa.option_id) IN (
		SELECT 
			msan.memberSurvey_id, 
			msan.question_id, 
			msan.option_id 
		FROM 
			pt_member_survey_answer msan 
		GROUP
 
 BY 
			msan.memberSurvey_id, 
			msan.question_id, 
			msan.option_id 
		HAVING 
			COUNT(*) > 1
	)
ORDER BY
	msa.memberSurvey_id ASC,
	msa.question_id ASC,
	msa.option_id ASC

刪除重複記錄

查詢涉及到重複情況的資料id

SELECT 
	msan.id AS 'id' 
FROM 
	pt_member_survey_answer msan 
GROUP BY 
	msan.memberSurvey_id, 
	msan.
 
question_id, 
	msan.option_id 
HAVING COUNT(*) > 1

刪除查詢到的資料id

1. 注意此處對上述查詢結果直接獲取的話，會丟擲 You can't specify target table for update in FROM clause 異常
2. 所以需要對查詢結果進行一次 SELECT 包裝，才可以
3. 刪除查詢結果只能查詢出可能重複的情況，如果同一個情況存在兩條或更多的重複資料，一次刪除無法完全清空，可能需要執行多次刪除語句

DELETE FROM
	pt_member_survey_answer
WHERE
	id IN (
		SELECT 
			rs.id 
		FROM (
			SELECT 
				msan.id AS 'id' 
			FROM 
				pt_member_survey_answer msan 
			GROUP BY 
				msan.memberSurvey_id, 
				msan.question_id, 
				msan.option_id 
			HAVING COUNT(*) > 1
		) rs
	)