向 SQL 查询添加自定义列

发布于 2024-11-08 21:50:46 字数 359 浏览 0 评论 0原文

假设我有一个像这样构建的数据库：

NUM    VALUE    
 1      3.51
 2      hello
 1      3.487
 2      goodbye
 1      32.4
 2      foo

我需要做什么来添加另一列，其中所有具有 num“2”的值都将在其中。

例如，

NUM     VALUE     value2
 1       3.51      hello      
 1       3.487     goodbye
 1      32.4       foo

知道如何做到这一点吗？谢谢！

原文

Lets say I have a DB built like this:

NUM    VALUE    
 1      3.51
 2      hello
 1      3.487
 2      goodbye
 1      32.4
 2      foo

what I need to do to add another column in which all the values having num "2" will be in.

e.g.

NUM     VALUE     value2
 1       3.51      hello      
 1       3.487     goodbye
 1      32.4       foo

any idea how I can do this?
thanks!

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空城旧梦 2024-11-15 21:50:46

在此示例中，我使用 SQLite，其中表 Source 已经具有内置 rowid。根据您使用的数据库，您可能需要添加自己的自动递增整数列（即整数主键），但想法是相同的。

CREATE TABLE Source (num, value);
INSERT INTO Source (num, value) VALUES (1, 3.51);
INSERT INTO Source (num, value) VALUES (2, 'hello');
INSERT INTO Source (num, value) VALUES (1, 3.487);
INSERT INTO Source (num, value) VALUES (2, 'goodbye');
INSERT INTO Source (num, value) VALUES (1, 32.4);
INSERT INTO Source (num, value) VALUES (2, 'foo');

"1","3.51"
"2","hello"
"1","3.487"
"2","goodbye"
"1","32.4"
"2","foo"

SELECT a.num, a.value, b.value
FROM Source a
INNER JOIN Source b ON a.rowid = b.rowid - 1
WHERE a.num = 1 AND b.num = 2

"1","3.51","hello"
"1","3.487","goodbye"
"1","32.4","foo"

In this example I am using SQLite, where the table Source already has a built-in rowid. Depending on the database you are using, you may need to add your own auto-incrementing integer column (i.e., integer primary key), but the idea is the same.

CREATE TABLE Source (num, value);
INSERT INTO Source (num, value) VALUES (1, 3.51);
INSERT INTO Source (num, value) VALUES (2, 'hello');
INSERT INTO Source (num, value) VALUES (1, 3.487);
INSERT INTO Source (num, value) VALUES (2, 'goodbye');
INSERT INTO Source (num, value) VALUES (1, 32.4);
INSERT INTO Source (num, value) VALUES (2, 'foo');

"1","3.51"
"2","hello"
"1","3.487"
"2","goodbye"
"1","32.4"
"2","foo"

SELECT a.num, a.value, b.value
FROM Source a
INNER JOIN Source b ON a.rowid = b.rowid - 1
WHERE a.num = 1 AND b.num = 2

"1","3.51","hello"
"1","3.487","goodbye"
"1","32.4","foo"

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