从一个表中选择与另一个表中的ID匹配的所有列

Question

I have a table structure like this

Customer

CustomerID|CustomerName|CustomerPhone|CustomerAddress
123       |Jason       |219632369    |4 pine street
485       |David       |219632369    |4 pine street
586       |Ramsay      |219632369    |4 pine street
779       |Jacob       |219632369    |4 pine street

Order

OrderID|CustomerID|ItemCode|ItemDesc
425    |123       |456     |Intel i7
427    |123       |456     |Intel i7
428    |485       |456     |Intel i7
429    |123       |456     |Intel i7
430    |485       |456     |Intel i7
431    |123       |456     |Intel i7

Expected output

CustomerID|CustomerName|CustomerPhone|CustomerAddress
123       |Jason       |219632369    |4 pine street
485       |David       |219632369    |4 pine street

I want to select all the columns from the customer table who have entries in orders table using the customerid

This is what I tried

select * 
from customer 
where customerid = (select customerid 
                      from order);

But this doesn't work.

Answer 1

Use Exists to search such customers since it avoids problems in case some order does not have a customerid specified. If some customerid is null in order the IN predicate is evaluated to unknown and it means that the no customer is returned.

select *
from customer c
where exists (
  select 1
  from "order" o
  where o.customerid = c.customerid 
)

Try to avoid using keywords for table names ( order ), it may cause unexpected troubles when writing SQL code.

Answer 2

您也可以使用内部联接来完成此操作，这只是一个附加解决方案：

select distinct cust.* from Customer cust inner join Order o on cust.CustomerID = o.CustomerID

Answer 3

Use the IN operator:

select * 
from customer
where customerid in (select customerid from order)

Answer 4

Try this

You have can create aliases for the tables, this is equal: select all from customer where customerid exists on orders

Select A.* from customer a, order b where a.customerid = b.customerid