sql - SQL Query 为每个项目提取一定数量的结果

Question

我正在寻找一种更好的方法来生成仅使用 sql 而不是 C# 的列表。看起来很简单，我做错了

假设我有一个名为 PhoneNumbers 的表，其中包含 Number/City/State

示例（但数百万个数字）：

NUMBER          CITY        STATE
555-555-5555    New York    NY
111-111-1111    Los Angeles CA
222-222-2222    Houston     TX
333-333-3333    Miami       FL

我需要一个从每个州返回 10 个电话号码的查询

现在我单独对所有 50 个状态运行查询，然后将它们组合到一个数据集中，但它是一个大数据库，所以它很慢，我希望有一个简单的方法来拉回我需要的数据。

Answer 1

The below query should work for Oracle and SQL Server, but not for MySQL:

with cte as
(select number, city, state,
 row_number() over (partition by state order by state) rn
 from yourtable)

select number,city,state
from cte
where rn <= 10

Note that if you need the first 10 rows sorted by a particular field, you will have to tweak the order by to suit your needs.

Answer 2

it differs, but for MSSQL:

with cteByStateas (
   select row_number() over (partition by STATE order by CITY) as RowNo,
          number,
          city,
          state
)
select * 
  from cteByState
 where RowNo <= 10

Please note that you didnt specify which first 10 numbers you want, or if they should be random

for mysql, there it is done a bit different, using a variable

Answer 3

您可以简单地使用UNION ALL子句。像这样的东西： -

(SELECT NUMBER, CITY, STATE FROM TABLE_NAME WHERE STATE = 'NY' ORDER BY CITY LIMIT 10)
UNION ALL
(SELECT NUMBER, CITY, STATE FROM TABLE_NAME WHERE STATE = 'CA' ORDER BY CITY LIMIT 10)
UNION ALL
(SELECT NUMBER, CITY, STATE FROM TABLE_NAME WHERE STATE = 'TX' ORDER BY CITY LIMIT 10)
UNION ALL
(SELECT NUMBER, CITY, STATE FROM TABLE_NAME WHERE STATE = 'FL' ORDER BY CITY LIMIT 10)

希望这可以帮到你。