SQL：将具有增量ID的列添加到SELECT

Question

我有简单的查询，如：

SELECT name FROM people;

people表没有唯一的id列。我想添加到查询结果列id，增量int从0/1开始无关紧要。怎么做到这一点？ （postgresql DB）

Answer 1

使用ROW_NUMBER()：

SQLFiddle

SELECT 
  name,
  ROW_NUMBER() OVER (ORDER BY name) AS id
FROM people;

修改

ORDER BY 1与ORDER BY column_name

之间的差异

SQLFiddleDemo

SELECT 
    name,
    ROW_NUMBER() OVER (ORDER BY name) AS id
FROM people;

/* Execution Plan */
QUERY PLAN WindowAgg (cost=83.37..104.37 rows=1200 width=38)
-> Sort (cost=83.37..86.37 rows=1200 width=38)
**Sort Key: name**
-> Seq Scan on people (cost=0.00..22.00 rows=1200 width=38)

SELECT 
    name,
    ROW_NUMBER() OVER (ORDER BY 1) AS id
FROM people;

/* Execution Plan */
QUERY PLAN WindowAgg (cost=0.00..37.00 rows=1200 width=38)
-> Seq Scan on people (cost=0.00..22.00 rows=1200 width=38)

在第二种情况下，没有排序操作。

您还可以将第二个查询写为：

SELECT 
    name,
    ROW_NUMBER() OVER () AS id
FROM people;

为什么人们在窗口函数中编写ORDER BY 1？

因为在某些方言中它是必需的，ORDER BY 1就像占位符一样。

Oracle：

  

ORA-30485：窗口规范中缺少ORDER BY表达式

SELECT 
  name,
  ROW_NUMBER() OVER (ORDER BY 1) AS id
FROM people;

TSQL：

  

函数'ROW_NUMBER'必须具有ORDER BY的OVER子句。

SELECT 
    name,
    ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS id
FROM people;

Answer 2

如果仅在运行查询时需要它，则可以使用row_number。

select row_number() over(order by name) as id, name
from people

Answer 3

row_number窗口功能应该适合账单：

SELECT ROW_NUMBER() OVER (ORDER BY 1), *
FROM   people

Answer 4

在https://www.postgresql.org/docs/current/static/functions-window.html

查看row_number()功能