如何制作SQL"IF-THEN-ELSE"语句

Question

我已经看到了关于SQL If-then-else东西的其他问题,但我没有看到如何将它与我想要做的事情联系起来.我已经使用SQL大约一年了,但只是基本的东西,从来没有.

如果我有一个看起来像这样的SQL表

|  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 |

如何编写SQL IF,ELSE语句,该语句创建一个遵循此规则的名为"Replication"的新列:

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)

结果表如下所示:

|  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 |

编辑:根据Sean Lange的回答,这是我第二次尝试解决方案:

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

的COALESCE是在那里时,有没有价值但在数列.

Answer 1

IF/Else构造用于控制t-sql中的语句流.您需要一个案例表达式,用于有条件地返回列中的值.

https://msdn.microsoft.com/en-us/library/ms181765.aspx

你的是这样的:

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