SQL語句執行過程
編碼原則：對於已有的代碼，我們要做到 對擴展開放，對修改關閉。
select <1> from <2> where <3> group by <4> having <5> order by <6> limit <7>
WHERE過濾→分組→聚合函數
******SQL的執行順序如下******
–第一步：執行 from
–第二步：分組前的條件過濾 where
–第三步：分組 group by
–第四步：執行投影列 select
–第五步：分組後的條件過濾 having
–第六步：執行排序 order by
–第七步：執行選擇幾行輸出 limit
MySQL學習路線
0、MySQL菜鳥教程
https://www.runoob.com/mysql/mysql-install.html
1、Mac上安裝MySQL
https://www.jianshu.com/p/0c701a4e7976
/usr/local/mysql/bin
(1)Use Strong Passord Encryption: MySQL root user pd=admin000111
(2)Use Legacy Passord Encryption: MySQL root user pd=admin0001112
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home
export PATH=$PATH:$JAVA_HOME/bin
export M2_HOME=/Library/maven/apache-maven-3.5.3
export PATH=$PATH:$M2_HOME/bin
export MYSQL_HOME=/usr/local/mysql
export PATH=$PATH:$MYSQL_HOME/bin
//登陸步驟：
source ~/.bash_profile
mysql -u root -p
密：admin0001112
2、解決MAC下每次都要執行soource ~/.bash_profile配置環境變量才能生效的問題
MySQL客戶端SequelPro連接數據庫失敗：https://www.jianshu.com/p/6b4fa7b87547
（1）官網：https://dev.mysql.com/downloads/mysql/、https://blog.csdn.net/RunIntoLove/article/details/51422787
（2）參考：https://jingyan.baidu.com/article/fa4125ac0e3c2928ac709204.html