您可以尝试将这些值加载到一个集合中，这样就可以进行查找，而无需每次都从数据库中提取数据。假设表没有被其他人更新，并且您有足够的内存。

# Let's assume you have a function runquery, that executes the

# provided statement and returns a collection of values as strings.

existing_values = set(runquery('SELECT DISTINCT value FROM table'))

with open('big_file.txt') as f:
    inserts = []
    updates = []
    for line in f:
        value = line.strip()
        if value in existing_values:
            updates.append(value)
        else:
            existing_values.add(value)
            inserts.append(value)
        if len(inserts) > THRESHOLD or len(updates) > THRESHOLD:
            # Do bulk updates and clear inserts and updates