Return one of the two columns in the view - whichever is not null

Question

I have a table with three columns:

ColumnA          ColumnB         ColumnC
AAA               NULL            123
BBB               222             NULL
CCC               NULL            NULL

I would like to create a SELECT statement that will return ColumnA and then a second column that will either show the value of ColumnB if ColumnB is not null; otherwise, it will display the ColumnC value, even if it is NULL. Can I use the IF statement for this? Sort of:

SELECT ColumnA, 
IF(ColumnB IS NULL, ColumnC, ColumnB)
FROM table

** If I get this working, the next step is to return the value of the merged column instead of column B. Essentially, the IF statement will be

IF(table.ColumnB IS NULL, table.ColumnC, table2.ColumnD)

Answer 1

Reading to the end of your question seems like you need to use CASE

CASE WHEN table.ColumnB IS NULL 
     THEN table.ColumnC 
     ELSE table2.ColumnD 
END AS Whatever

Answer 2

Use COALESCE

SELECT ColumnA, COALESCE(ColumnB, ColumnC) as 'Value'