mysql 5.7版本 only_full_group_by 1055错误及 sql_mode 解析

以前项目的数据库是5.5版本的，以后升级到了5.6.没有什么问题。可是最近由于实施部环境的时候，直接给用成了mysql5.7版本，结果项目启动直接就出问题了。最终把问题解决以后，在我本地环境也进行了设置，如今把过程记录一下：

最开始报出来的结果是：

错误代码1055。不过看了Expression里面的缘由描述，我基本知道怎么回事了。缘由是由于mysql中对 group by 用法的规定。严格意义上说，就是group by以后。select 的字段只能是group by的字段。或者须要加聚合函数的。在 oracle 中，一直有这项约定。因此直接就会报错。可是mysql 直到 5.7 版本以后才把这个要求明确限制起来。

很明显，这种问题两种思路：第一修改sql。按照规定的规范重写项目中全部有问题的sql。很明显代价太大。风险很高；第二种那就是把这种限制去掉，让功能继续像5.7以前的样子同样能跑。我果断选择了第二种。由于第一种代价太大。

解决办法：

1. 首先如何查看当前数据库使用的sql_mode：

select @@sql_mode; 

2. 修改mysql的配置文件，删掉only_full_group_by这一项

注意：Mac：Mysql默认安装在/usr/local目录下，这个目录能够经过command+shift+G进入：以下图

windows下是的配置文件是my.ini，本身能够找一下。

问题解决完了，而后剩下两个问题：

1. mysql里面的 sql_mode 一共有哪些，而且mode的值各自表明什么含义。在网上查询了一下，结果以下：

MySQL5.0以上版本支持三种sql_mode模式：ANSI、TRADITIONAL和STRICT_TRANS_TABLES
一、ANSI模式：宽松模式，更改语法和行为，使其更符合标准SQL。对插入数据进行校验，若是不符合定义类型或长度，对数据类型调整或截断保存，报warning警告。对于本文开头中提到的错误，能够先把sql_mode设置为ANSI模式，这样即可以插入数据，而对于除数为0的结果的字段值，数据库将会用NULL值代替。
将当前数据库模式设置为ANSI模式：切换到mysql命令下执行：set @@sql_mode=ANSI;  

二、TRADITIONAL模式：严格模式，当向mysql数据库插入数据时，进行数据的严格校验，保证错误数据不能插入，报error错误，而不只仅是警告。用于事物时，会进行事物的回滚。 注释：一旦发现错误当即放弃INSERT/UPDATE。若是你使用非事务存储引擎，这种方式不是你想要的，由于出现错误前进行的数据更改不会“滚动”，结果是更新“只进行了一部分”。
将当前数据库模式设置为TRADITIONAL模式：切换到mysql命令下执行：set @@sql_mode=TRADITIONAL; 

三、STRICT_TRANS_TABLES模式：严格模式，进行数据的严格校验，错误数据不能插入，报error错误。若是不能将给定的值插入到事务表中，则放弃该语句。对于非事务表，若是值出如今单行语句或多行语句的第1行，则放弃该语句。
将当前数据库模式设置为STRICT_TRANS_TABLES模式：切换到mysql命令下执行：set @@sql_mode=STRICT_TRANS_TABLES;  

mode值的含义：
  ONLY_FULL_GROUP_BY：对于GROUP BY聚合操做，若是在SELECT中的列，没有在GROUP BY中出现，那么将认为这个SQL是不合法的，由于列不在GROUP BY从句中

  STRICT_TRANS_TABLES：在该模式下，若是一个值不能插入到一个事务表中，则中断当前的操做，对非事务表不作任何限制

  NO_ZERO_IN_DATE：在严格模式，不接受月或日部分为0的日期。若是使用IGNORE选项，咱们为相似的日期插入'0000-00-00'。在非严格模式，能够接受该日期，但会生成警告。

  NO_ZERO_DATE：在严格模式，不要将 '0000-00-00'作为合法日期。你仍然能够用IGNORE选项插入零日期。在非严格模式，能够接受该日期，但会生成警告

  ERROR_FOR_DIVISION_BY_ZERO：在严格模式，在INSERT或UPDATE过程当中，若是被零除(或MOD(X，0))，则产生错误(不然为警告)。若是未给出该模式，被零除时MySQL返回NULL。若是用到INSERT IGNORE或UPDATE IGNORE中，MySQL生成被零除警告，但操做结果为NULL。

  NO_AUTO_CREATE_USER：防止GRANT自动建立新用户，除非还指定了密码。

  NO_ENGINE_SUBSTITUTION：若是须要的存储引擎被禁用或未编译，那么抛出错误。不设置此值时，用默认的存储引擎替代，并抛出一个异常

2. 顺便找到 mysql 的配置文件了，里面的配置项分别表明什么含义呢。也查询了一下，结果以下：

#
# The following options will be read by the MySQL Server. Make sure that
# you have installed the server correctly (see above) so it reads this 
# file.
#
[mysqld]

# The TCP/IP Port the MySQL Server will listen on
port=3306


#Path to installation directory. All paths are usually resolved relative to this.
basedir="E:/Java/Mysql/"

#Path to the database root
datadir="C:/ProgramData/MySQL/MySQL Server 5.5/Data/"

# The default character set that will be used when a new schema or table is
# created and no character set is defined
character-set-server=gb2312

# The default storage engine that will be used when create new tables when
default-storage-engine=INNODB

# Set the SQL mode to strict
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"

# The maximum amount of concurrent sessions the MySQL server will
# allow. One of these connections will be reserved for a user with
# SUPER privileges to allow the administrator to login even if the
# connection limit has been reached.
max_connections=100

# Query cache is used to cache SELECT results and later return them
# without actual executing the same query once again. Having the query
# cache enabled may result in significant speed improvements, if your
# have a lot of identical queries and rarely changing tables. See the
# "Qcache_lowmem_prunes" status variable to check if the current value
# is high enough for your load.
# Note: In case your tables change very often or if your queries are
# textually different every time, the query cache may result in a
# slowdown instead of a performance improvement.
query_cache_size=0

# The number of open tables for all threads. Increasing this value
# increases the number of file descriptors that mysqld requires.
# Therefore you have to make sure to set the amount of open files
# allowed to at least 4096 in the variable "open-files-limit" in
# section [mysqld_safe]
table_cache=256

# Maximum size for internal (in-memory) temporary tables. If a table
# grows larger than this value, it is automatically converted to disk
# based table This limitation is for a single table. There can be many
# of them.
tmp_table_size=35M


# How many threads we should keep in a cache for reuse. When a client
# disconnects, the client's threads are put in the cache if there aren't
# more than thread_cache_size threads from before.  This greatly reduces
# the amount of thread creations needed if you have a lot of new
# connections. (Normally this doesn't give a notable performance
# improvement if you have a good thread implementation.)
thread_cache_size=8

#*** MyISAM Specific options

# The maximum size of the temporary file MySQL is allowed to use while
# recreating the index (during REPAIR, ALTER TABLE or LOAD DATA INFILE.
# If the file-size would be bigger than this, the index will be created
# through the key cache (which is slower).
myisam_max_sort_file_size=100G

# If the temporary file used for fast index creation would be bigger
# than using the key cache by the amount specified here, then prefer the
# key cache method.  This is mainly used to force long character keys in
# large tables to use the slower key cache method to create the index.
myisam_sort_buffer_size=69M

# Size of the Key Buffer, used to cache index blocks for MyISAM tables.
# Do not set it larger than 30% of your available memory, as some memory
# is also required by the OS to cache rows. Even if you're not using
# MyISAM tables, you should still set it to 8-64M as it will also be
# used for internal temporary disk tables.
key_buffer_size=55M

# Size of the buffer used for doing full table scans of MyISAM tables.
# Allocated per thread, if a full scan is needed.
read_buffer_size=64K
read_rnd_buffer_size=256K

# This buffer is allocated when MySQL needs to rebuild the index in
# REPAIR, OPTIMZE, ALTER table statements as well as in LOAD DATA INFILE
# into an empty table. It is allocated per thread so be careful with
# large settings.
sort_buffer_size=256K


如下是参数的简介：

port参数也是表示数据库的端口。

basedir参数表示MySQL的安装路径。

datadir参数表示MySQL数据文件的存储位置，也是数据库表的存放位置。

default-character-set参数表示默认的字符集，这个字符集是服务器端的。

default-storage-engine参数默认的存储引擎。

sql-mode参数表示SQL模式的参数，经过这个参数能够设置检验SQL语句的严格程度。

max_connections参数表示容许同时访问MySQL服务器的最大链接数，其中一个链接是保留的，留给管理员专用的。

query_cache_size参数表示查询时的缓存大小，缓存中能够存储之前经过select语句查询过的信息，再次查询时就能够直接从缓存中拿出信息。

table_cache参数表示全部进程打开表的总数。

tmp_table_size参数表示内存中临时表的总数。

thread_cache_size参数表示保留客户端线程的缓存。

myisam_max_sort_file_size参数表示MySQL重建索引时所容许的最大临时文件的大小。

myisam_sort_buffer_size参数表示重建索引时的缓存大小。

key_buffer_size参数表示关键词的缓存大小。

read_buffer_size参数表示MyISAM表全表扫描的缓存大小。

read_rnd_buffer_size参数表示将排序好的数据存入该缓存中。

sort_buffer_size参数表示用于排序的缓存大小

上面是mysql服务器的一些参数，此外，参数中还有关于InnoDB存储引擎使用的参数，以下

#*** INNODB Specific options ***


# Use this option if you have a MySQL server with InnoDB support enabled
# but you do not plan to use it. This will save memory and disk space
# and speed up some things.
#skip-innodb

# Additional memory pool that is used by InnoDB to store metadata
# information.  If InnoDB requires more memory for this purpose it will
# start to allocate it from the OS.  As this is fast enough on most
# recent operating systems, you normally do not need to change this
# value. SHOW INNODB STATUS will display the current amount used.
innodb_additional_mem_pool_size=3M

# If set to 1, InnoDB will flush (fsync) the transaction logs to the
# disk at each commit, which offers full ACID behavior. If you are
# willing to compromise this safety, and you are running small
# transactions, you may set this to 0 or 2 to reduce disk I/O to the
# logs. Value 0 means that the log is only written to the log file and
# the log file flushed to disk approximately once per second. Value 2
# means the log is written to the log file at each commit, but the log
# file is only flushed to disk approximately once per second.
innodb_flush_log_at_trx_commit=1

# The size of the buffer InnoDB uses for buffering log data. As soon as
# it is full, InnoDB will have to flush it to disk. As it is flushed
# once per second anyway, it does not make sense to have it very large
# (even with long transactions).
innodb_log_buffer_size=2M

# InnoDB, unlike MyISAM, uses a buffer pool to cache both indexes and
# row data. The bigger you set this the less disk I/O is needed to
# access data in tables. On a dedicated database server you may set this
# parameter up to 80% of the machine physical memory size. Do not set it
# too large, though, because competition of the physical memory may
# cause paging in the operating system.  Note that on 32bit systems you
# might be limited to 2-3.5G of user level memory per process, so do not
# set it too high.
innodb_buffer_pool_size=107M

# Size of each log file in a log group. You should set the combined size
# of log files to about 25%-100% of your buffer pool size to avoid
# unneeded buffer pool flush activity on log file overwrite. However,
# note that a larger logfile size will increase the time needed for the
# recovery process.
innodb_log_file_size=54M

# Number of threads allowed inside the InnoDB kernel. The optimal value
# depends highly on the application, hardware as well as the OS
# scheduler properties. A too high value may lead to thread thrashing.
innodb_thread_concurrency=18

innodb_additional_mem_pool_size参数表示附加的内存池，用来存储InnoDB表的内容。

innodb_flush_log_at_trx_commit参数是设置提交日志的时机，若设置为1，InnoDB会在每次提交后将事务日志写到磁盘上。

innodb_log_buffer_size参数表示用来存储日志数据的缓存区的大小。

innodb_buffer_pool_size参数表示缓存的大小，InnoDB使用一个缓冲池类保存索引和原始数据。

innodb_log_file_size参数表示日志文件的大小。

innodb_thread_concurrency参数表示在InnoDB存储引擎容许的线程最大数。