MySQL Python：JSON 类型在赋值时引发错误

Question

I am unable to update JSON type cells with ON DUPLICATE KEY UPDATE , as an error is thrown. I am using mysql-connector-python . Here is a minimal (not)working example:

First, I define my table as:

cursor = db.cursor()
cursor.execute('''
    CREATE TABLE test (
        id INT AUTO_INCREMENT PRIMARY KEY,
        foo VARCHAR(255) NOT NULL UNIQUE,
        bar JSON NOT NULL
    )
''')

Then I try to insert values into the table:

val = [
    {
        'foo': 'lorem ipsum',
        'bar': json.dumps({'a': 1}),
    },
    {
        'foo': 'dolor sit amet',
        'bar': json.dumps({'a': 2}),
    },
]
sql = '''
    INSERT INTO test
        (foo, bar)
    VALUES
        (%(foo)s, %(bar)s)
    ON DUPLICATE KEY UPDATE 
        bar = %(bar)s
'''
cursor = db.cursor()
cursor.executemany(sql, val)

Which leads to an error:

ProgrammingError: 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '%(bar)s' at line 6

If I change the line that says bar = %(bar)s to bar = \\'%(bar)s\\' , the code happily executes... at least for the first time, until I run this section again to invoke the ON DUPLICATE KEY UPDATE clause, which then results in another error:

DataError: 3140 (22032): Invalid JSON text: "Invalid value." at position 0 in value for column 'test.bar'.

Could you, please, advise me how to fix my syntax?

Answer 1

You could use the VALUES function in the UPDATE clause as well:

In assignment value expressions in the ON DUPLICATE KEY UPDATE clause, you can use the VALUES(col_name) function to refer to column values from the INSERT portion of the INSERT ... ON DUPLICATE KEY UPDATE statement. In other words, VALUES(col_name) in the ON DUPLICATE KEY UPDATE clause refers to the value of col_name that would be inserted, had no duplicate-key conflict occurred. This function is especially useful in multiple-row inserts.

sql = '''
    INSERT INTO test
        (foo, bar)
    VALUES
        (%(foo)s, %(bar)s)
    ON DUPLICATE KEY UPDATE 
        bar = VALUES(bar)
'''