It makes sense, but I found no relation to the question.

The APPLY operator is similar to a JOIN but with additional capabilities. It allows you to reference columns from tables previously used in the FROM clause.

Now, let's compare the code.

SELECT at.ID,

u.Step,

u.CompletedDate,

u.FollowupDate

FROM #Activity_Tracking at

CROSS APPLY( VALUES('Step1', Step1_C, Step1_F),

('Step2', Step2_C, Step2_F),

('Step3', Step3_C, Step3_F),

('Step4', Step4_C, Step4_F))u(Step,CompletedDate,FollowupDate);

SELECT A.Id, B.Name, C.State, D.Step, D.FollowupDate, D.CompletedDate

from

A left outer join on A.ID = B.ID

Inner Join C on A.ID = C.ID

at Cross Apply (Values

('step1', step1_F, Step1_C)

('step2', step2_F, Step2_C)

('step3', step3_F, Step3_C)

('step4', step4_F, Step4_C)) as D(Step,FollowupDate, CompletedDate)

Can you spot the errors and differences? Maybe if we format it the same way, the 3 errors will become easier to spot.

SELECT A.Id,

B.Name,

C.State,

D.Step,

D.FollowupDate,

D.CompletedDate

FROM A

LEFT OUTER JOIN ON A.ID = B.ID

INNER JOIN C ON A.ID = C.ID at

CROSS APPLY (VALUES ('step1', step1_F, Step1_C)

('step2', step2_F, Step2_C)

('step3', step3_F, Step3_C)

('step4', step4_F, Step4_C)) as D(Step,FollowupDate, CompletedDate)

Remember, you need to understand the code that you're using, that's why I'm not giving you the full answer and want you to find it.