如何从同一个表的两列查询等于一个值

Question

I have a mysql table as follow

id|  reagent1  | reagent 2
1 |  coffee    |  milk
2 |  sugar     |  coffee
3 |  coffee    |  salt

If I would like to get the reagents of coffee, the result should be

reagentofcoffee
milk
sugar
salt

How can I make a query to get expected result? I am new to mysql and I have tried many time.

Answer 1

You can use case :

select case when reagent1 = 'coffee' then reagent2 
            when reagent2 = 'coffee' then reagent1 end as reagentofcoffee
from tbl

Answer 2

SELECT IF(reagent1 = 'coffee',reagent1,reagent2) as reagent FROM table WHERE reagent1 = 'coffee' OR reagent2 = 'coffee'

Answer 3

A case expression in the select list should do the trick:

SELECT CASE reagent1 WHEN 'coffee' THEN reagent2 ELSE reagent1 END
           AS reagentofcoffee
FROM   reagents
WHERE  'coffee' IN (reagent1, reagent2)