计数MySQL表中的重复记录？
您可以if()从MySQL使用计数重复的记录。语法如下-
SELECT yourColumnName, COUNT(*) AS anyVariableName, IF ( COUNT(*)>1,"Duplicate Records", "Not Duplicate records") as anyVariableName FROM yourTableName group by yourColumnName;
为了理解上述语法，让我们创建一个表。创建表的查询如下-
mysql> create table DuplicateRecords -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(30), -> PRIMARY KEY(Id) -> );
使用insert命令在表中插入一些记录。查询如下-
mysql> insert into DuplicateRecords(Name) values('Carol');
mysql> insert into DuplicateRecords(Name) values('John');
mysql> insert into DuplicateRecords(Name) values('Sam');
mysql> insert into DuplicateRecords(Name) values('John');
mysql> insert into DuplicateRecords(Name) values('Sam');
mysql> insert into DuplicateRecords(Name) values('Sam');
mysql> insert into DuplicateRecords(Name) values('John');
mysql> insert into DuplicateRecords(Name) values('Carol');
mysql> insert into DuplicateRecords(Name) values('Carol');
mysql> insert into DuplicateRecords(Name) values('Mike');使用select语句显示表中的所有记录。查询如下-
mysql> select *from DuplicateRecords;
以下是输出-
+----+-------+ | Id | Name | +----+-------+ | 1 | Carol | | 2 | John | | 3 | Sam | | 4 | John | | 5 | Sam | | 6 | Sam | | 7 | John | | 8 | Carol | | 9 | Carol | | 10 | Mike | +----+-------+ 10 rows in set (0.00 sec)
这是查询表中重复记录的查询-
mysql> SELECT Name, COUNT(*) AS Repetition, IF (COUNT(*)>1,"Duplicate Records", "Not Duplicate records") as IsDuplicateRecordsOrNot -> from DuplicateRecords group by Name;
以下是输出-
+-------+------------+-------------------------+ | Name | Repetition | IsDuplicateRecordsOrNot | +-------+------------+-------------------------+ | Carol | 3 | Duplicate Records | | John | 3 | Duplicate Records | | Sam | 3 | Duplicate Records | | Mike | 1 | Not Duplicate records | +-------+------------+-------------------------+ 4 rows in set (0.00 sec)
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