从3列获取DISTINCT值

Question

I have 1 single table with 3 columns say col1,col2,col3

VALUES:

col1 with values (in individual 3 rows) as a, b, c
col2 with values (in individual 3 rows) as b, c, d
col3 with values (in individual 3 rows) as c, d, e

AIM:

To get distinct list to populate in html drop down box (ie i want a,b,c,d,e) in alphabetical order ?

Answer 1

Pseudocode:

Select col1 from table
UNION
Select col2 from table
UNION
Select col3 from table