mysql 5.7版本 only_full_group_by 1055錯誤及 sql_mode 解析

以前項目的數據庫是5.5版本的，以後升級到了5.6.沒有什麼問題。可是最近由於實施部環境的時候，直接給用成了mysql5.7版本，結果項目啓動直接就出問題了。最終把問題解決以後，在我本地環境也進行了設置，如今把過程記錄一下：

最開始報出來的結果是：

錯誤代碼1055。不過看了Expression裏面的緣由描述，我基本知道怎麼回事了。緣由是由於mysql中對 group by 用法的規定。嚴格意義上說，就是group by以後。select 的字段只能是group by的字段。或者須要加聚合函數的。在 oracle 中，一直有這項約定。因此直接就會報錯。可是mysql 直到 5.7 版本以後才把這個要求明確限制起來。

很明顯，這種問題兩種思路：第一修改sql。按照規定的規範重寫項目中全部有問題的sql。很明顯代價太大。風險很高；第二種那就是把這種限制去掉，讓功能繼續像5.7以前的樣子同樣能跑。我果斷選擇了第二種。由於第一種代價太大。

解決辦法：

1. 首先如何查看當前數據庫使用的sql_mode：

select @@sql_mode; 

2. 修改mysql的配置文件，刪掉only_full_group_by這一項

注意：Mac：Mysql默認安裝在/usr/local目錄下，這個目錄能夠經過command+shift+G進入：以下圖

windows下是的配置文件是my.ini，本身能夠找一下。

問題解決完了，而後剩下兩個問題：

1. mysql裏面的 sql_mode 一共有哪些，而且mode的值各自表明什麼含義。在網上查詢了一下，結果以下：

MySQL5.0以上版本支持三種sql_mode模式：ANSI、TRADITIONAL和STRICT_TRANS_TABLES
一、ANSI模式：寬鬆模式，更改語法和行爲，使其更符合標準SQL。對插入數據進行校驗，若是不符合定義類型或長度，對數據類型調整或截斷保存，報warning警告。對於本文開頭中提到的錯誤，能夠先把sql_mode設置爲ANSI模式，這樣即可以插入數據，而對於除數爲0的結果的字段值，數據庫將會用NULL值代替。
將當前數據庫模式設置爲ANSI模式：切換到mysql命令下執行：set @@sql_mode=ANSI;  

二、TRADITIONAL模式：嚴格模式，當向mysql數據庫插入數據時，進行數據的嚴格校驗，保證錯誤數據不能插入，報error錯誤，而不只僅是警告。用於事物時，會進行事物的回滾。 註釋：一旦發現錯誤當即放棄INSERT/UPDATE。若是你使用非事務存儲引擎，這種方式不是你想要的，由於出現錯誤前進行的數據更改不會「滾動」，結果是更新「只進行了一部分」。
將當前數據庫模式設置爲TRADITIONAL模式：切換到mysql命令下執行：set @@sql_mode=TRADITIONAL; 

三、STRICT_TRANS_TABLES模式：嚴格模式，進行數據的嚴格校驗，錯誤數據不能插入，報error錯誤。若是不能將給定的值插入到事務表中，則放棄該語句。對於非事務表，若是值出如今單行語句或多行語句的第1行，則放棄該語句。
將當前數據庫模式設置爲STRICT_TRANS_TABLES模式：切換到mysql命令下執行：set @@sql_mode=STRICT_TRANS_TABLES;  

mode值的含義：
  ONLY_FULL_GROUP_BY：對於GROUP BY聚合操做，若是在SELECT中的列，沒有在GROUP BY中出現，那麼將認爲這個SQL是不合法的，由於列不在GROUP BY從句中

  STRICT_TRANS_TABLES：在該模式下，若是一個值不能插入到一個事務表中，則中斷當前的操做，對非事務表不作任何限制

  NO_ZERO_IN_DATE：在嚴格模式，不接受月或日部分爲0的日期。若是使用IGNORE選項，咱們爲相似的日期插入'0000-00-00'。在非嚴格模式，能夠接受該日期，但會生成警告。

  NO_ZERO_DATE：在嚴格模式，不要將 '0000-00-00'作爲合法日期。你仍然能夠用IGNORE選項插入零日期。在非嚴格模式，能夠接受該日期，但會生成警告

  ERROR_FOR_DIVISION_BY_ZERO：在嚴格模式，在INSERT或UPDATE過程當中，若是被零除(或MOD(X，0))，則產生錯誤(不然爲警告)。若是未給出該模式，被零除時MySQL返回NULL。若是用到INSERT IGNORE或UPDATE IGNORE中，MySQL生成被零除警告，但操做結果爲NULL。

  NO_AUTO_CREATE_USER：防止GRANT自動建立新用戶，除非還指定了密碼。

  NO_ENGINE_SUBSTITUTION：若是須要的存儲引擎被禁用或未編譯，那麼拋出錯誤。不設置此值時，用默認的存儲引擎替代，並拋出一個異常

2. 順便找到 mysql 的配置文件了，裏面的配置項分別表明什麼含義呢。也查詢了一下，結果以下：

#
# 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


如下是參數的簡介：

port參數也是表示數據庫的端口。

basedir參數表示MySQL的安裝路徑。

datadir參數表示MySQL數據文件的存儲位置，也是數據庫表的存放位置。

default-character-set參數表示默認的字符集，這個字符集是服務器端的。

default-storage-engine參數默認的存儲引擎。

sql-mode參數表示SQL模式的參數，經過這個參數能夠設置檢驗SQL語句的嚴格程度。

max_connections參數表示容許同時訪問MySQL服務器的最大鏈接數，其中一個鏈接是保留的，留給管理員專用的。

query_cache_size參數表示查詢時的緩存大小，緩存中能夠存儲之前經過select語句查詢過的信息，再次查詢時就能夠直接從緩存中拿出信息。

table_cache參數表示全部進程打開表的總數。

tmp_table_size參數表示內存中臨時表的總數。

thread_cache_size參數表示保留客戶端線程的緩存。

myisam_max_sort_file_size參數表示MySQL重建索引時所容許的最大臨時文件的大小。

myisam_sort_buffer_size參數表示重建索引時的緩存大小。

key_buffer_size參數表示關鍵詞的緩存大小。

read_buffer_size參數表示MyISAM表全表掃描的緩存大小。

read_rnd_buffer_size參數表示將排序好的數據存入該緩存中。

sort_buffer_size參數表示用於排序的緩存大小

上面是mysql服務器的一些參數，此外，參數中還有關於InnoDB存儲引擎使用的參數，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參數表示附加的內存池，用來存儲InnoDB表的內容。

innodb_flush_log_at_trx_commit參數是設置提交日誌的時機，若設置爲1，InnoDB會在每次提交後將事務日誌寫到磁盤上。

innodb_log_buffer_size參數表示用來存儲日誌數據的緩存區的大小。

innodb_buffer_pool_size參數表示緩存的大小，InnoDB使用一個緩衝池類保存索引和原始數據。

innodb_log_file_size參數表示日誌文件的大小。

innodb_thread_concurrency參數表示在InnoDB存儲引擎容許的線程最大數。