计算MySQL中有多少行具有相同的值？
要使用功能COUNT（*）和GROUPBY计算多少行具有相同的值。语法如下-
SELECT yourColumName1, count(*) as anyVariableName from yourTableName GROUP BY yourColumName1;
为了理解上述语法，让我们首先创建一个表。创建表的查询如下-
mysql> create table RowWithSameValue −> ( −> StudentId int, −> StudentName varchar(100), −> StudentMarks int −> );
插入一些具有相同值的记录。在此，我们为示例中的多个学生添加了相同的标记。插入记录的查询如下-
mysql> insert into RowWithSameValue values(100,'Carol',89); mysql> insert into RowWithSameValue values(101,'Sam',89); mysql> insert into RowWithSameValue values(102,'John',99); mysql> insert into RowWithSameValue values(103,'Johnson',89);
现在，您可以显示我们在上面插入的所有记录。显示所有记录的查询如下-
mysql> select *from RowWithSameValue;
以下是输出-
+-----------+-------------+--------------+ | StudentId | StudentName | StudentMarks | +-----------+-------------+--------------+ | 100 | Carol | 89 | | 101 | Sam | 89 | | 102 | John | 99 | | 103 | Johnson | 89 | +-----------+-------------+--------------+ 4 rows in set (0.00 sec)
实施我们开头讨论的语法以对具有相同值的行进行计数-
mysql> SELECT StudentMarks, count(*) as SameValue from RowWithSameValue GROUP BY StudentMarks;
以下是显示多个值的计数的输出-
+--------------+-----------+ | StudentMarks | SameValue | +--------------+-----------+ | 89 | 3 | | 99 | 1 | +--------------+-----------+ 2 rows in set (0.00 sec)