常见关系运算符

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在本章中，我们将讨论建立在关系之上的运算符。

__eq__()

上面的运算符是多对一的“等于”比较。该运算符的代码行如下所示 -

s = session.query(Customer).filter(Invoice.invno.__eq__(12))

上述代码行的等效 SQL 查询是 -

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers, invoices
WHERE invoices.invno = ?

__ne__()

该运算符是多对一的“不等于”比较。该运算符的代码行如下所示 -

s = session.query(Customer).filter(Invoice.custid.__ne__(2))

上述代码行的等效 SQL 查询如下 -

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers, invoices
WHERE invoices.custid != ?

包含（）

该运算符用于一对多集合，下面给出的是 contains() 的代码 -

s = session.query(Invoice).filter(Invoice.invno.contains([3,4,5]))

上述代码行的等效 SQL 查询是 -

SELECT invoices.id 
AS invoices_id, invoices.custid 
AS invoices_custid, invoices.invno 
AS invoices_invno, invoices.amount 
AS invoices_amount
FROM invoices
WHERE (invoices.invno LIKE '%' + ? || '%')

任何（）

any() 运算符用于集合，如下所示 -

s = session.query(Customer).filter(Customer.invoices.any(Invoice.invno==11))

上述代码行的等效 SQL 查询如下所示 -

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE EXISTS (
   SELECT 1
   FROM invoices
   WHERE customers.id = invoices.custid 
   AND invoices.invno = ?)

有（）

该运算符用于标量引用，如下所示 -

s = session.query(Invoice).filter(Invoice.customer.has(name = 'Arjun Pandit'))

上述代码行的等效 SQL 查询是 -

SELECT invoices.id 
AS invoices_id, invoices.custid 
AS invoices_custid, invoices.invno 
AS invoices_invno, invoices.amount 
AS invoices_amount
FROM invoices
WHERE EXISTS (
   SELECT 1
   FROM customers
   WHERE customers.id = invoices.custid 
   AND customers.name = ?)