通过使用 DISTINCT 关键字和列名作为 COUNT() 函数的参数，我们可以计算列中唯一值的数量。语法如下 -
SELECT COUNT(DISTINCT Col_name) FROM table_name;
示例
假设我们有下表
mysql> Select * from tender; +----------+--------------+--------------+-------+ | clientid | client_Fname | Client_Lname | value | +----------+--------------+--------------+-------+ | 100 | Mohan | Kumar | 60000 | | 101 | Sohan | Singh | 50000 | | 101 | Somil | Rattan | 55000 | | 103 | Gaurav | Kumar | 75000 | | 103 | Rahul | Singh | 63000 | +----------+--------------+--------------+-------+ 5 rows in set (0.00 sec)
现在，如果我们想要计算名为“clientid”的列中唯一值的总数，则可以借助以下查询来完成 -
mysql> Select COUNT(DISTINCT Clientid) from tender; +--------------------------+ | COUNT(DISTINCT Clientid) | +--------------------------+ | 3 | +--------------------------+ 1 row in set (0.00 sec)
如果我们想计算名为“Client_Lname”的列中唯一值的总数，则可以借助以下查询来完成 -
mysql> Select COUNT(DISTINCT Client_Lname) from tender; +------------------------------+ | COUNT(DISTINCT Client_Lname) | +------------------------------+ | 3 | +------------------------------+ 1 row in set (0.00 sec)
