zoukankan      html  css  js  c++  java
  • MySQL Boolean类型的坑

    MySQL中,Boolean只是 tinyint(1) 的别名,也就是说,MySQL中并没有真正的bool类型。

    而SQLAlchemy生成SQL的时候并没有检测到 这一点,这就导致一个问题,当使用 bool 类型作为查询条件时,用不上索引,从而导致扫表的行为:

    > SELECT COUNT(*) FROM message WHERE message.is_national = 1
     AND message.updated_at > '2020-01-01 00:00:00' AND message.deleted_at IS NULL;
    +----------+
    | COUNT(*) |
    +----------+
    | 0        |
    +----------+
    1 row in set
    Time: 0.018s
    > SELECT COUNT(*) FROM message WHERE message.is_national is true 
    AND message.updated_at > '2020-01-01 00:00:00' AND message.deleted_at IS NULL;
    +----------+
    | COUNT(*) |
    +----------+
    | 0        |
    +----------+
    1 row in set
    Time: 2.162s
    sql

    注意观察第一行和第二行的时间,很明显第二行没有用上索引,我们来看看 EXPLAIN 的结果便知道了:

    > EXPLAIN SELECT COUNT(*) FROM message WHERE message.is_national = 1 AND message.updated_at > '2020-01-01 00:00:00' AND message.de
            leted_at IS NULL;
    | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
    | 1  | SIMPLE | message | ref  | ix_message_updated_at,idx_updated_at_is_national,ix_message_is_national | ix_message_is_national | 1 | const | 1 | Using where |
    

    > EXPLAIN SELECT COUNT(*) FROM message WHERE message.is_national is true AND message.updated_at > '2020-01-01 00:00:00' AND messag
    e.deleted_at IS NULL;
    | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
    | 1 | SIMPLE | message | ALL | ix_message_updated_at,idx_updated_at_is_national | <null> | <null> | <null> | 一个很大的数字 | Using whe
    re
    |

    explain

    mysql文档给出的解释

    java.lang.Boolean if the configuration property tinyInt1isBit is set to true (the default) and the storage size is 1, or java.lang.Integer if not.

    要注意下面这个提示

    The ResultSet.getObject() method uses the type conversions between MySQL and Java types, following the JDBC specification where appropriate. The values returned by ResultSetMetaData.GetColumnTypeName()and ResultSetMetaData.GetColumnClassName() are shown in the table below. For more information on the JDBC types, see the reference on the java.sql.Types class.

    文档地址:https://dev.mysql.com/doc/connector-j/8.0/en/connector-j-reference-type-conversions.html

    解决方案:

    1.使用ifnull(column, 0)处理该字段,个人测试过可以;
    2.在JDBC的URL增加 tinyInt1isBit=false参数,注意参数名区分大小写,否则不生效(默认为true)
    即:jdbc:mysql://${ucmha.proxy1_2.host}/${db.mysql.db}?tinyInt1isBit=false
    3.避免使用长度为1的tinyint类型字段存储数字格式的数据;


    参考资料:


     

  • 相关阅读:
    oracle入门
    转-nginx详解
    VNX磁盘状态分析
    Linux下确定哪个网卡对应哪个接口?
    企业运维人员最常用150个linux命令汇总
    linux系统LVM管理-逻辑卷扩容
    VNX1代-VNX2代
    VNX-SPS电池
    VNX存储系统,在磁盘做rebuilding的时候是否可以更换故障硬盘?
    Ubuntu系统挂载大于2T新硬盘方法
  • 原文地址:https://www.cnblogs.com/zt007/p/14663816.html
Copyright © 2011-2022 走看看