Count number of unique characters in a string

Question

I\'m looking for a sql statement to count the number of unique characters in a string.

e.g.

3333333333 -> returns 1
1113333333 -> returns 2
111         


        

Answer 1

One thing you can do is have a table of all your characters, such as:

mysql> select * from chars;
+----+------+
| id | c    |
+----+------+
|  1 | 1    |
|  2 | 2    |
|  3 | 3    |
|  4 | 4    |
+----+------+

If your table of words looks like this:

mysql> select * from words;
+----+-----------+
| id | word      |
+----+-----------+
|  1 | 111222333 |
|  2 | 11111111  |
|  3 | 2222111   |
|  4 | 5555555   |
+----+-----------+

You can then join these tables on the condition of the character being in the word, and get the count, like this:

mysql> select word, count(c) from words w inner join chars c on locate(c.c, word) group by word;
+-----------+----------+
| word      | count(c) |
+-----------+----------+
| 11111111  |        1 |
| 111222333 |        3 |
| 2222111   |        2 |
+-----------+----------+