Question

假设我有一个查询某些表company.workers的函数，例如（伪代码）：

def sql_query(dept, prof, hireDate):
    q = """SELECT *
            FROM company.workers
            WHERE department = {0} 
            AND profession = {1} 
            AND hire_date > {2}""".format(dept, prof, hireDate)
   cur.execute(q)
   return cur

如果我想仅允许用户在dept和prof上进行查询，hireDate是可选的，该怎么办？这是我提出的解决方案：

def sql_query(dept, prof, *args):
    if args:
        q = """SELECT *
                FROM company.workers
                WHERE department = {0} 
                AND profession = {1} 
                AND hire_date > {2}""".format(dept, prof, args[0])
    else:
        q = """SELECT *
                FROM company.workers
                WHERE department = {0} 
                AND profession = {1} """.format(dept, prof)
    cur.execute(q)
    return cur
#the function could be called as so:
sql_query('20', 'Engineer', (2017-12-10))

但我认为这是次要的。如果我想允许多个可选 coloumns进行查询，该怎么办？如果我把它做成两个，我有4个选项可以处理，这是很多else-if块。有更高效/更优雅的解决方案吗？

Answer 1

您不会说出您正在使用的SQL DBMS，但这是一块接受三个变量的SQL Server样式代码块：

@dept
@prof
@hireDate

WHERE子句总是使用@dept和@prof，如果它不为null，则只使用@hireDate。

SELECT 
    *
FROM 
    company.workers
WHERE 
    department = @dept
AND 
    profession = @prof 
AND 
(
    (
        @hireDate IS NOT NULL AND hire_date = @hireDate
        )
OR @hireDate IS NULL
)

然后，您可以根据需要使用相同的样式添加任意数量的其他选项变量，而不是为每个组合编写单独的SQL语句。

Answer 2

类似问题here。你是对的，你真的不想手动生成语句。您可以使用字典使其更具动态性来改进当前代码：

def sql_query(**params):
    q = "SELECT * FROM company.workers"
    count=0
    for i in non_require_param:
        if count==0:
            q += " WHERE {0} = {1} ".format(i, params[i])
        else:
            q += " AND {0} = {1} ".format(i, params[i])
        count += 1
    cur.execute(q)
    return cur

此外，sqlite's execute cursor是值得研究的。它比自己格式化语句更清晰，并处理数据类型转换：

who = "Yeltsin"
age = 72
cur.execute("""select * from company.workers 
            where name_last=:name_last and age=:age""",
            {"name_last": who, "age": age})

使用可选的“where”子句创建SQL查询函数

2 个答案: