sql - 尝试优化嵌套的 PostgreSQL WHERE IN

Question

我有一个类似于以下内容的 Postgres (9.1) 客户数据库:

customers.id
customers.lastname
customers.firstname

invoices.id
invoices.customerid
invoices.total

invoicelines.id
invoicelines.invoiceid
invoicelines.itemcode
invoicelines.price

我构建了一个搜索，其中列出了购买了特定商品(例如“abc”)的所有客户。

Select * from customers WHERE customers.id IN
    (Select invoices.customerid FROM invoices WHERE invoices.id IN
        (Select invoicelines.invoiceid FROM invoicelines WHERE
        invoicelines.itemcode = 'abc')
    )

搜索工作正常并找到正确的客户，但在包含 200 万张发票和 200 万行项目的数据库上大约需要 10 秒左右。

我想知道是否有另一种方法可以稍微减少一点。

Answer 1

另一种方法是使用 EXISTS:

Select * 
from customers 
WHERE EXISTS (
   Select invoices.customerid 
   FROM invoices 
   JOIN invoicelines
      ON invoicelines.invoiceid = invoices.id AND
         invoicelines.itemcode = 'abc' AND
         customers.id = invoices.customerid)