sql 查询表中特定重复数据的函数包括：count 函数：计算重复值的数量。group by 子句：分组数据并计算每个组中的值。having 子句：筛选聚合查询的结果。

SQL 中查询表中特定重复数据的函数

COUNT 函数

COUNT 函数可计算表中重复值的数量。语法：

COUNT(column_name)

示例:

若要计算 "customers" 表中 "city" 列中 "New York" 的出现次数：

SELECT COUNT(city) FROM customers WHERE city = 'New York';

GROUP BY 子句

GROUP BY 子句可将数据分组，然后应用聚合函数（如 COUNT）计算每个组中的值。语法：

SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name

示例:

若要找出 "customers" 表中按城市分组的客户数量：

SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city;

HAVING 子句

HAVING 子句可筛选聚合查询的结果。语法：

SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name
HAVING COUNT(*) > value

示例:

若要找出 "customers" 表中客户数量大于 500 个的城市：

SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city
HAVING customer_count > 500;

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