Replace existing strings with new text in other columns

[louyang]

Hi there,

In the table below, I'm tring to replace existing strings in Column A and B with text in Column C and D.

There are 3 cases in the table:

1. Column A and B have null values, I want to replace them with Column C and D texts.

2. Column A and B have strings, I want to replace them with Column C and D texts.

3. Column A and B have strings, but null values in Column C and D, I want to keep existing strings in Column A and B.

So for case 1 I have successfully used the Isnull function to replace the null values in Column A and B, and for case 3 I don't need to do anything.

But for Case 2, I have no idea how to use the replace function or any other tools. Appreciate if you can help on this.

[SzymonDK]

From what you described here, I would simply use the NOT operator before the IsNull() function. If it's not null then it contains a string, therefore we should replace it. 
Something like this:

[Peachyco · Accepted solution]

I think the more straightforward test is if C/D has a value: If C/D is not null, perform the swap, else A/B keeps its value. This should cover all three cases.

Like this (for Column A):

IF !IsNull([Column C]) THEN [Column C] ELSE [Column A] ENDIF

[louyang]

Thank you so much guys for offering the logic behind and the formulas @SzymonDK @Peachyco !

I have taken Peachyco's method as it is more straightforward and I just have to switch the column names in the formula and it worked! Sometimes just need to think the other way.