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sql 查詢表中特定重復(fù)數(shù)據(jù)的函數(shù)包括：count 函數(shù)：計(jì)算重復(fù)值的數(shù)量。group by 子句：分組數(shù)據(jù)并計(jì)算每個組中的值。having 子句：篩選聚合查詢的結(jié)果。

SQL 中查詢表中特定重復(fù)數(shù)據(jù)的函數(shù)

COUNT 函數(shù)

COUNT 函數(shù)可計(jì)算表中重復(fù)值的數(shù)量。語法：

<code class="sql">COUNT(column_name)</code>

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示例:

若要計(jì)算 “customers” 表中 “city” 列中 “New York” 的出現(xiàn)次數(shù)：

<code class="sql">SELECT COUNT(city) FROM customers WHERE city = 'New York';</code>

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GROUP BY 子句

GROUP BY 子句可將數(shù)據(jù)分組，然后應(yīng)用聚合函數(shù)（如 COUNT）計(jì)算每個組中的值。語法：

<code class="sql">SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name</code>

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示例:

若要找出 “customers” 表中按城市分組的客戶數(shù)量：

<code class="sql">SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city;</code>

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HAVING 子句

HAVING 子句可篩選聚合查詢的結(jié)果。語法：

<code class="sql">SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name
HAVING COUNT(*) &gt; value</code>

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示例:

若要找出 “customers” 表中客戶數(shù)量大于 500 個的城市：

<code class="sql">SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city
HAVING customer_count &gt; 500;</code>

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