不要计算MySql数据库中的重复条目[重复]

Question

This question already has an answer here:

• MySQL: Count unique pairs of values in rows 1 answer

I have a MySQL Table like this:

+-----------+--------------+------+-----+------------------+-------+
| Field     | Type         | Null | Key | Default          | Extra |
+-----------+--------------+------+-----+------------------+-------+
| _m        | int(1)       | NO   |     | 0                |       |
| Timestamp | int(11)      | NO   | PRI | 0                |       |
| Address   | varchar(8)   | NO   | PRI | 0000000a         |       |
| Message   | varchar(255) | NO   | PRI | <NO_MESSAGE>     |       |
| Location  | varchar(100) | NO   |     | <NEED_TO_BE_SET> |       |
+-----------+--------------+------+-----+------------------+-------+

There are Columns like this:

+-----------+---------+-----------------+
| Timestamp | Address | Message         |
+-----------+---------+-----------------+
| 000000001 | A       | Some Text       |
| 000000001 | B       | Some Text       |
| 000000002 | H       | Some Other Text |
| 000000005 | I       | Some Third Text |
+-----------+---------+-----------------+

(I've removed "_m" and "Location" because it's not necessary. Timestamp and Address are censored because its sensitive data)

This table contains signals.
There can be one unique signals which are send to multiple Addreses (Like row 1 and 2)

A unique signal is (should ... be) represented by a unique entriy in the "Message" Field. In this case there

How can i count only the unique signals? (In this case there are 3 of them)

</div>

Answer 1

you can use:

    select count(distinct message) from your_table