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

There is no direct or easy way of doing it. You may need to write a store function to do the job and by looking at all the characters you may expect in the data. Here is an example for just digits , which could be extended for all the characters in a stored function

mysql> select * from test ;
+------------+
| val        |
+------------+
| 11111111   |
| 111222222  |
| 1113333222 |
+------------+


select 
val, 
sum(case when locate('1',val) > 0 then 1 else 0 end ) 
+ sum( case when locate('2',val) > 0 then 1 else 0 end)
+ sum(case when locate('3',val) > 0 then 1 else 0 end)
+sum(case when locate('4',val) > 0 then 1 else 0 end ) as occurence
from test group by val


+------------+-----------+
| val        | occurence |
+------------+-----------+
| 11111111   |         1 |
| 111222222  |         2 |
| 1113333222 |         3 |
+------------+-----------+

Or if you have enough time , create a lookup table with all the characters you could think of. And make the query in 2 lines

mysql> select * from test ;
+------------+
| val        |
+------------+
| 11111111   |
| 111222222  |
| 1113333222 |
+------------+
3 rows in set (0.00 sec)

mysql> select * from look_up ;
+------+------+
| id   | val  |
+------+------+
|    1 | 1    |
|    2 | 2    |
|    3 | 3    |
|    4 | 4    |
+------+------+
4 rows in set (0.00 sec)

select 
t1.val, 
sum(case when locate(t2.val,t1.val) > 0 then 1 else 0 end ) as occ 
from test t1,(select * from look_up)t2 
group by t1.val ;

+------------+------+
| val        | occ  |
+------------+------+
| 11111111   |    1 |
| 111222222  |    2 |
| 1113333222 |    3 |
+------------+------+