Random Numbers/Random Record:
The discussion on random numbers for banners have been discussed several
times, and in several ways. Getting a random record (a la jump.cgi) has
been asked a few times. In the next release of MySQL (current 3.23.xx.beta)
There is a RAND() function that can be used in a Select statement:
> SELECT * FROM table_name ORDER BY RAND() Limit 1
Would return a single random record. Limit 5, would return 5 random records.
.

Count & Distinct
> Select COUNT(DISTINCT Field_name) FROM Table_name
Would return the count of distinct field names.
.
> Select COUNT(*) FROM people WHERE sex='M'
Would return the number of "Male" records in the table 'people'.
.
> Select sex, COUNT(*) FROM people GROUP BY sex
Would return a table with the number of M values and number of F values:
M | nn
F | nn
.
and finally,
.
> Select ID, Name, COUNT(*) AS count FROM Category
-> GROUP BY Name HAVING count > 1 ORDER BY count DESC
Would show which category Names in the Category table were duplicated.
ie: duplicate categories. (note: the -> means "continued" and should not
be typed into your query) You'd then:
> Select ID, Name from Category where Name = 'name_found_above'
to get the ID's of the records that needed merging, or just type the
name into the Links Admin and it would show both Category Records.
.