MySQL聚合函数操作NULL字段要小心
1.COUNT(expr)
Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. The result is a BIGINT value. … [阅读文章]
聊技术聊人生
聊技术聊人生
Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. The result is a BIGINT value. … [阅读文章]