自动增量作为SQL中的计数器

Question

I have a table with 3 columns (imageId, reportId, counter) the primary key of the table is the columns (imageId, reportId) now I want the counter columns will be the counter of how many times i've tried to insert the pair (imageId, reportId).

for example if i have the image "x.png" and 100 people reported that this image contains pornography, i want that the row in the table with the value ("x.png", "pornography") will have 100 in the counter column. when the next person will report this image as pornography I want the counter to be 101 and so on.

how can i do such thing?

thank you

Answer 1

In this scenario it would be best to add new rows to your table. This means you can provide a view over the top of this which can select the counts as you require.

The benefit of a new row per report is the ability to also allow users to add custom messages etc.

-- Update

Some details here on views here http://dev.mysql.com/doc/refman/5.0/en/view-syntax.html

At the heart of it your query will just be a basic query like

SELECT imageId, reportId, count(reportId) as count FROM training.reporttable group by imageId, reportId

Here is a basic example:

Note, I stuck with your example data but reportId and imageId should be normalised

Answer 2

Use INSERT ... ON DUPLICATE KEY UPDATE

INSERT IGNORE INTO table (imageId, reportId, counter) VALUES (1, 1, 0) ON DUPLICATE KEY UPDATE SET counter=counter+1

You could also set the default value of the counter column to 0 and use this:

INSERT IGNORE INTO table (imageId, reportId) VALUES (1, 1) ON DUPLICATE KEY UPDATE SET counter=counter+1