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可以使用 sql 的 group by 和 count() 函數(shù)、distinct 和 count() 函數(shù)或窗口函數(shù) row_number() 來查詢重復(fù)字段數(shù)據(jù)。

SQL 查詢重復(fù)字段數(shù)據(jù)

問題：如何使用 SQL 查詢重復(fù)字段數(shù)據(jù)？

回答：

在 SQL 中，可以使用以下方法查詢重復(fù)字段數(shù)據(jù)：

方法 1：使用 GROUP BY 和 COUNT() 函數(shù)

SELECT field_name, COUNT(*) AS count_duplicates
FROM table_name
GROUP BY field_name
HAVING COUNT(*) > 1

登錄后復(fù)制

示例：

SELECT customer_id, COUNT(*) AS count_duplicates
FROM orders
GROUP BY customer_id
HAVING COUNT(*) > 1;

登錄后復(fù)制

方法 2：使用 DISTINCT 和 COUNT() 函數(shù)

SELECT field_name
FROM table_name
GROUP BY field_name
HAVING COUNT(DISTINCT field_name) <p><strong>示例：</strong></p><pre class="brush:php;toolbar:false">SELECT customer_id
FROM orders
GROUP BY customer_id
HAVING COUNT(DISTINCT customer_id) <p><strong>方法 3：使用窗口函數(shù) ROW_NUMBER()</strong></p><pre class="brush:php;toolbar:false">SELECT field_name, ROW_NUMBER() OVER (PARTITION BY field_name ORDER BY field_name) AS row_number
FROM table_name
WHERE row_number &gt; 1

登錄后復(fù)制

示例：

SELECT customer_id, ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY customer_id) AS row_number
FROM orders
WHERE row_number > 1;

登錄后復(fù)制

解釋：

上述方法使用 SQL 函數(shù)和子句來分組數(shù)據(jù)并計算重復(fù)值。GROUP BY 子句將數(shù)據(jù)按字段名稱分組，COUNT() 函數(shù)計算每個組中重復(fù)項的數(shù)量。HAVING 子句篩選出重復(fù)項計數(shù)大于 1 的組。DISTINCT 關(guān)鍵字可確保只計算每個組中唯一值。ROW_NUMBER() 窗口函數(shù)為每組中的行分配一個順序號，并可以用來識別重復(fù)行。