oracle IF ELSE 语句并插入新列
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/26510998/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
IF ELSE Statement and Insert a new Column
提问by Futochan
I've been trying research online on how to combine "If" statements into my query. Suppose I wanted to create a query such that I want to create a extra column called "Description", and then include a if else statement such that "If Value = "A" then Description = "A", If Value = "B" then Description = "B", so on and so on. The problem is, since I have minimal access (not admin) to the databases. I can't create tables. I can only query the tables in oracles and export it out. Will that be an issue in terms of creating an extra column?
我一直在尝试在线研究如何将“If”语句组合到我的查询中。假设我想创建一个查询，以便创建一个名为“Description”的额外列，然后包含一个 if else 语句，使得“If Value = “A” then Description = “A”, If Value = “B”然后Description =“B”，依此类推。问题是，因为我对数据库的访问权限最小（不是管理员）。我无法创建表。我只能在oracles中查询表并将其导出。就创建额外的列而言，这会是一个问题吗？
Original:
原来的：
ID Value
1 A
2 B
3 C
Want something like:
想要这样的东西：
ID Value Description(New Column)
1 A Apple
2 B Bacon
3 C Candy
Okay. I have no idea what I was doing below but it would be something like that? Where to I insert a new column called "Description"?
好的。我不知道我在下面做什么，但它会是那样的吗？在哪里插入一个名为“描述”的新列？
Select A.ID, B.Value
From Table A
Join Table B
On A.ID = B.ID
Where ID in ('1','2','3')
If b.Value = 'A' then
(Description = "Apple")
If b. value = 'B' then
(Description = "Bacon")
Group by A.ID, B.Value
回答by Barmar
You can use CASE:
您可以使用CASE：
SELECT A.ID, B.Value,
CASE B.Value
WHEN 'A' THEN 'Apple'
WHEN 'B' THEN 'Bacon'
WHEN 'C' THEN 'Candy'
END AS Description
FROM TableA A
JOIN TableB B ON A.ID = B.ID
回答by radar
you can do it like below
你可以像下面那样做
SELECT A.ID, A.Value, B.Description
FROM TABLEA A
JOIN ( SELECT 'A' as Value, 'Apple' as Description from dual
UNION
SELECT 'B' as Value, 'Bacon' as Description from dual
) T
on A.Value= B.Value
回答by Bacs
I'm not sure why you need to join the table to itself. Also, I presume you're not really trying to do this with a table named "table".
我不知道为什么你需要加入表格本身。另外，我认为您并没有真正尝试使用名为“table”的表来执行此操作。
CASE would do the job, as in Barmar's answer. I find DECODE more readable when the logic is this simple, but it's really a matter of taste. CASE is more flexible, which is not a matter of taste, but you don't need that flexibility here.
CASE 可以完成这项工作，就像 Barmar 的回答一样。当逻辑如此简单时，我发现 DECODE 更具可读性，但这确实是一个品味问题。CASE 更灵活，这不是品味的问题，但您不需要这里的灵活性。
select id
,value
,decode( value
,'A', 'Apple'
,'B', 'Bacon'
,'C', 'Candy' ) as Description
from table;
