Get count of values that only appear once in a MySQL column?

To get number of values that only appear once in a column, use GROUP BY HAVING. Let us first create a table:

mysql> create table DemoTable
(
   Name varchar(20)
);
Query OK, 0 rows affected (0.55 sec)

Following is the query to insert some records in the table using insert command:

mysql> insert into DemoTable values('Larry');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('Larry');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Sam');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Chris');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Sam');
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('Sam');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Larry');
Query OK, 1 row affected (0.21 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.32 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('Carol');
Query OK, 1 row affected (0.27 sec)
mysql> insert into DemoTable values('Robert');
Query OK, 1 row affected (0.27 sec)

Following is the query to display records from the table using select command:

mysql> select *from DemoTable;

This will produce the following output

+--------+
| Name |
+--------+
| Larry |
| Larry |
| Sam |
| Chris |
| Sam |
| Mike |
| Sam |
| Larry |
| Mike |
| Mike |
| Carol |
| Robert |
+--------+
12 rows in set (0.00 sec)

Following is the query to count the values that only appear once in a column i.e. the count of the names that appears only once in the “Name” column:

mysql> SELECT COUNT(Name)
FROM (
   SELECT Name
   FROM DemoTable
   GROUP BY Name
   HAVING COUNT(*) = 1
) AS APPEAR_FIRST_TIME;

This will produce the following output

+-------------+
| COUNT(Name) |
+-------------+
|           3 |
+-------------+
1 row in set (0.00 sec)

Krantik Chavan

Published on 29-Apr-2019 07:59:19