How to make a SQL "IF-THEN-ELSE" statement

Question

I've seen other questions about SQL If-then-else stuff, but I'm not seeing how to relate it to what I'm trying to do. I've been using SQL for about a year now but only basic stuff and never this.

If I have a SQL table that looks like this

|  Name | Version | Category | Value | Number |
|:-----:|:-------:|:--------:|:-----:|:------:|
| File1 | 1.0     | Time     |   123 |      1 |
| File1 | 1.0     | Size     |   456 |      1 |
| File1 | 1.0     | Final    |   789 |      1 |
| File2 | 1.0     | Time     |   312 |      1 |
| File2 | 1.0     | Size     |   645 |      1 |
| File2 | 1.0     | Final    |   978 |      1 |
| File3 | 1.0     | Time     |   741 |      1 |
| File3 | 1.0     | Size     |   852 |      1 |
| File3 | 1.0     | Final    |   963 |      1 |
| File1 | 1.1     | Time     |   369 |      2 |
| File1 | 1.1     | Size     |   258 |      2 |
| File1 | 1.1     | Final    |   147 |      2 |
| File2 | 1.1     | Time     |   741 |      2 |
| File2 | 1.1     | Size     |   734 |      2 |
| File2 | 1.1     | Final    |   942 |      2 |
| File3 | 1.1     | Time     |   997 |      2 |
| File3 | 1.1     | Size     |   997 |      2 |
| File3 | 1.1     | Final    |   985 |      2 |

How can I write a SQL IF, ELSE statement that creates a new column called "Replication" that follows this rule:

A = B + 1 when x = 1
else 
A = B

where A = the number we will use for the next Number
B = Max(Number)
x = Replication count (this is the number of times that a loop is executed. x=i)

The results table will look like this:

|  Name | Version | Category | Value | Number | Replication |
|:-----:|:-------:|:--------:|:-----:|:------:|:-----------:|
| File1 | 1.0     | Time     |   123 |      1 |           1 |
| File1 | 1.0     | Size     |   456 |      1 |           1 |
| File1 | 1.0     | Final    |   789 |      1 |           1 |
| File2 | 1.0     | Time     |   312 |      1 |           1 |
| File2 | 1.0     | Size     |   645 |      1 |           1 |
| File2 | 1.0     | Final    |   978 |      1 |           1 |
| File1 | 1.0     | Time     |   369 |      1 |           2 |
| File1 | 1.0     | Size     |   258 |      1 |           2 |
| File1 | 1.0     | Final    |   147 |      1 |           2 |
| File2 | 1.0     | Time     |   741 |      1 |           2 |
| File2 | 1.0     | Size     |   734 |      1 |           2 |
| File2 | 1.0     | Final    |   942 |      1 |           2 |
| File1 | 1.1     | Time     |   997 |      2 |           1 |
| File1 | 1.1     | Size     |   997 |      2 |           1 |
| File1 | 1.1     | Final    |   985 |      2 |           1 |
| File2 | 1.1     | Time     |   438 |      2 |           1 |
| File2 | 1.1     | Size     |   735 |      2 |           1 |
| File2 | 1.1     | Final    |   768 |      2 |           1 |
| File1 | 1.1     | Time     |   786 |      2 |           2 |
| File1 | 1.1     | Size     |   486 |      2 |           2 |
| File1 | 1.1     | Final    |   135 |      2 |           2 |
| File2 | 1.1     | Time     |   379 |      2 |           2 |
| File2 | 1.1     | Size     |   943 |      2 |           2 |
| File2 | 1.1     | Final    |   735 |      2 |           2 |

EDIT: Based on the answer by Sean Lange, this is my 2nd attempt at a solution:

SELECT COALESCE(MAX)(Number) + CASE WHEN Replication = 1 then 1 else 0, 1) FROM Table

The COALESCE is in there for when there is no value yet in the Number column.

Answer 1

The IF/Else construct is used to control flow of statements in t-sql. You want a case expression, which is used to conditionally return values in a column.

Yours would be something like:

case when x = 1 then A else B end as A