SQL如何有效地使用wheresomething!=something？

Question

所以我有 3 张 table ，

Companies (company_id, company_name)
Stock_Exchanges(stock_exchange_id, stock_exchange_name, stock_exchange_manager)
Stock_Exchanges_Companies(stock_exchange_id, company_id)

我正在尝试选择不在特定 stock_exchange 上的所有公司。

到目前为止我有这个:

SELECT COMPANY_NAME
  FROM COMPANIES c
  LEFT OUTER JOIN STOCK_EXCHANGES_COMPANIES sec 
    ON c.COMPANY_ID = sec.COMPANY_ID
  LEFT OUTER JOIN STOCK_EXCHANGES se 
    ON sec.STOCK_EXCHANGE_ID = se.STOCK_EXCHANGE_ID
 WHERE sec.COMPANY_ID != se.COMPANY_ID;

当我使用 WHERE 子句时，它返回零行。任何帮助将不胜感激!

Answer 1

嘿伙计们，我成功解决了这个问题!

我添加了一个额外的 AND 子句:

SELECT COMPANY_NAME
FROM COMPANIES c
LEFT OUTER JOIN STOCK_EXCHANGES_COMPANIES sec ON c.COMPANY_ID = sec.COMPANY_ID
LEFT OUTER JOIN STOCK_EXCHANGES se ON sec.STOCK_EXCHANGE_ID = se.STOCK_EXCHANGE_ID
WHERE sec.COMPANY_ID != se.COMPANY_ID
    AND sec.stock_exchange_id != idhere;