insert NULL into mysql

https://stackoverflow.com/questions/36898130/python-how-to-insert-null-mysql-values

You are inserting the string 'NULL', not the NULL value. If these values are coming from a Python structure, you need to use something else to map to the NULL value in SQL.

You could use None for this, and only quote other values:

def sqlquote(value):
    """Naive SQL quoting

    All values except NULL are returned as SQL strings in single quotes,
    with any embedded quotes doubled.

    """
    if value is None:
         return 'NULL'
    return "'{}'".format(str(value).replace("'", "''"))

sql = "INSERT INTO test VALUES ({column1}, {column2}, {column3})".format(
    **{k: sqlquote(v) for k, v in d.items()})

Note that because you have to handle None differently, you also have to handle proper SQL quoting! If any of your values directly or indirectly come from user-supplied data, you'd be open for SQL injection attacks otherwise.

The above sqlquote() function should suffice for SQLite strings, which follow standard SQL quoting rules. Different databases have different rules for this, so tripple check your documentation.

Personally, I'd use the SQLAlchemy library to generate SQL and have it handle quoting for you. You can configure it to produce SQL for different database engines.

插入空的datetime类型：

sql = "INSERT INTO test_data_table (`data`, char_test, datetime_test) VALUES (%s, %s, %s)" % ('NULL', 'NULL', "'2017-09-01'")

sql = "INSERT INTO test_data_table (`data`, char_test, datetime_test) VALUES (%s, %s, %s)" % ('NULL', 'NULL', 'NULL')
注意两者之间的不同。

简而言之，python遇到None，需要在数据库插入'NULL'需要有一个转化过程，将None转为NULL，并视情况加单双引号，不加''在%s.

数字插入空值

INSERT INTO company (company_id,  name, employee_nums) values (%s, %s, %s) on duplicate key update company_id = values(company_id), name=values(name), employee_nums=values(employee_nums);

args = (1, "test_name", None)  # None will be convert to NULL

conn._cur.execute(sql, arg)

# 再次更新，%s全部不加引号，在传值之前处理完毕

INSERT INTO company (company_id,  name, employee_nums， registered_date) 

values (%s, %s, %s, %s) 

on duplicate key update company_id = values(company_id), name=values(name), employee_nums=values(employee_nums), 

registered_date=values(registered_date); % （company_id, name, employee_name, "'{}'".format(registered_date) if registred_date else "NULL"）