高大上技术之sql解析

Question: 为何sql解析和高大上有关系？
Answer：因为数据库永远都是系统的核心，CRUD如此深入码农的内心。。。如果能把CRUD改造成高大上技术，如此不是造福嘛。。。

CRUD就是Create, Read, Update, Delete，转换成sql语句就是insert, select, update, delete

普通场景下，insert也就是一个insert了，没什么高深。。。
高并发场景下，insert就不是一个insert了，而是千千万万个insert。。。可以用到的技术有排队、分表、分区、分仓、缓存同步

普通场景下，select也就是一个select了，没什么高深。。。
高并发场景下，select就不是一个select了，而是千千万万，再千千万万个select。。。可以用到的技术有缓存、普通读写分离、深入读写分离、不锁、past锁、还有分表、分区、分仓。。。

你说这么多东西，是全部在一个sql中全部自动化掉好呢，还是让我们码农一个一个考虑，再一个一个写成代码逻辑的好？

肯定两种声音都有，还肯定有第三种声音。。。所以我还是照着我自己的思路来说吧，你们随便发挥想象。。。

我要让一个sql全部解决上面的效果，或者接近上面的效果

如何解决，那就是，以SELECT语句为例

1. 解析SELECT语句
2. 解析牵涉到的表、字段、主键
3. 解析是否用到了自己扩展的dsl函数
4. 找到相应表的分区函数
5. 找到相应表的缓存配置
6. 找到dsl函数对应的真实函数
7. 其他

比如有2个SELECT语句：

1. SELECT UserID, UserName, Age FROM Users WHERE UserID='某个guid'
2. SELECT COUNT(1) FROM Users

很简单的两句sql，可是Users是个虚拟表，真实表有16个表：Users.[A-F], Users.[0-9],分表策略为根据主键ID的第一个字母来分表, 因此：

• 第一句sql需要先解析where条件中UserID='guid'这个UserID是否为pkid，以及这个'guid'的值，然后根据guid的值调用分表策略函数得到相应的分表后缀，然后用类似下面这个sql来真实查询：SELECT UserID, UserName, Age FROM [Users.A] WHERE UserID='axxxxx-xxxxx-xxxx-xx'
• 第二句sql其实是最终变成了16条sql来得到各个分表的count值，然后在程序中累加这些分表的count值

其他：

• 其他类似缓存、队列、自定义的扩展函数，都类似于上可以得到解决。

由于只是个demo，所以没有实现上述全部功能，我们只说下关键原理、和代码。。。

我们用antlr来做词法解析、语法解析，然后再用tree walker把antlr解析出来的东西转换为我们要的数据结构，比如：SelectTerms, TableName, WhereClause, OrderByClause等

奥，我们还得写一个规则文件让Antlr吃进去，然后antlr就能调用tree walker生成我们要的数据结构了

（大家赶紧补下编译原理之类的基础知识以及ANTLR知识） 

grammar SelectSQL;

/*
 * Parser Rules
 */

compileUnit
    :    start
    ;

/*
 * Lexer Rules
 */

WS
    :    [ 	

]+ -> skip
    ;



COMMA:',';
SELECT: 'SELECT';
STAR:'*';
FROM:'FROM';
WHERE:'WHERE';
ORDERBY:'ORDER BY';
DIRECTION:'ASC'|'DESC';
CHAR: 'a'..'z'|'A'..'Z';
NUM: '0'..'9';
STRING:''' .*? ''';
LB:'(';
RB:')';
LBRACE:'[';
RBRACE:']';
CONDITIONS_OPERATOR    
    :'AND'
    |'OR'
    ;
CONDITION_OPERATOR    
    :'='
    |'>'
    |'<'
    |'<>'
    |'!='
    |'>='
    |'<='
    ;
FCOUNT:'COUNT';


start
    :statement_list
    ;

statement_list
    :statement statement*
    ;

statement
    :selectStatement
    ;


selectStatement
    :selectStmt fromStmt whereStmt? orderbyStmt?
    ;

selectStmt
    :SELECT columns
    ;

columns
    :column (COMMA column)*
    ;

column
    : identifier
    | LBRACE identifier RBRACE
    | functionStmt
    | STAR
    ;

functionStmt
    :function LB (parameters) RB
    ;
    
function
    :FCOUNT
    ;

parameters
    : parameter (COMMA parameter)*
    ;

parameter
    : identifier
    | integer
    | string
    | STAR
    ;

fromStmt
    :FROM table
    ;

table
    : identifier
    | LBRACE identifier RBRACE
    ;


whereStmt
    : WHERE conditions
    ;
    
conditions
    : condition (CONDITIONS_OPERATOR condition)* 
    ;

condition
    :left CONDITION_OPERATOR right
    ;
    
left
    : parameter
    ;
    
right
    : parameter
    ;
    
orderbyStmt
    :ORDERBY sortStmt
    ;

sortStmt
    : sortCondition (COMMA sortCondition)*
    ;
    
sortCondition
    :sortColumn DIRECTION
    ;

sortColumn
    : identifier
    | LBRACE identifier RBRACE
    ;

identifier
    :CHAR (CHAR|NUM)*
    ;
integer
    :NUM+
    ;
string
    : STRING
    ;

 真心呼唤广大开发人员深入编译原理之类的基础技术！

在eclipse中输入解析sql文本后，会被解析成tree

 开源世界真强大啊，有yacc, flex, bison, antlr这些现成的解析工具。

 我们先在eclipse中把规则测试通过后，再把这个.g4规则文件拷贝到我们的visual studio中，如下：

然后只要这个g4文件一保存，antlr的vs插件就会自动根据规则文件生成相关名称的词法解析类、文法解析类、以及我们即将要改写的TreeListener

SelectSQLBaseListener：就是antlr插件自动生成的抽象类，我们的改动都是基于这个类，来做override改写（针对规则的enter/exit） 

EnterXXXXX/ExitXXXX: 对应规则文件中的规则名称，Enter/Exit代表进入规则以及离开规则之前的行为动作

demo控制台程序运行输出效果：

输入SQL:

                    SELECT * FROM users
                    SELECT userId, userName FROM users
                    SELECT COUNT(1) FROM users
                    SELECT COUNT(*) FROM users
                    SELECT userId, userName FROM users ORDER BY userName DESC
                    SELECT userId, userName FROM users WHERE userId='1212121' ORDER BY userName DESC

输出SQL:
          select * from [users.0]
          select * from [users.1]
          select * from [users.2]
          select * from [users.3]
          select * from [users.4]
          select * from [users.5]
          select * from [users.6]
          select * from [users.7]
          select * from [users.8]
          select * from [users.9]
          select * from [users.a]
          select * from [users.b]
          select * from [users.c]
          select * from [users.d]
          select * from [users.e]
          select * from [users.f]
          select userId, userName from [users.0]
          select userId, userName from [users.1]
          select userId, userName from [users.2]
          select userId, userName from [users.3]
          select userId, userName from [users.4]
          select userId, userName from [users.5]
          select userId, userName from [users.6]
          select userId, userName from [users.7]
          select userId, userName from [users.8]
          select userId, userName from [users.9]
          select userId, userName from [users.a]
          select userId, userName from [users.b]
          select userId, userName from [users.c]
          select userId, userName from [users.d]
          select userId, userName from [users.e]
          select userId, userName from [users.f]
          select COUNT(1) from [users.0]
          select COUNT(1) from [users.1]
          select COUNT(1) from [users.2]
          select COUNT(1) from [users.3]
          select COUNT(1) from [users.4]
          select COUNT(1) from [users.5]
          select COUNT(1) from [users.6]
          select COUNT(1) from [users.7]
          select COUNT(1) from [users.8]
          select COUNT(1) from [users.9]
          select COUNT(1) from [users.a]
          select COUNT(1) from [users.b]
          select COUNT(1) from [users.c]
          select COUNT(1) from [users.d]
          select COUNT(1) from [users.e]
          select COUNT(1) from [users.f]
          select COUNT(*) from [users.0]
          select COUNT(*) from [users.1]
          select COUNT(*) from [users.2]
          select COUNT(*) from [users.3]
          select COUNT(*) from [users.4]
          select COUNT(*) from [users.5]
          select COUNT(*) from [users.6]
          select COUNT(*) from [users.7]
          select COUNT(*) from [users.8]
          select COUNT(*) from [users.9]
          select COUNT(*) from [users.a]
          select COUNT(*) from [users.b]
          select COUNT(*) from [users.c]
          select COUNT(*) from [users.d]
          select COUNT(*) from [users.e]
          select COUNT(*) from [users.f]
          select userId, userName from [users.0]  order by userName DESC
          select userId, userName from [users.1]  order by userName DESC
          select userId, userName from [users.2]  order by userName DESC
          select userId, userName from [users.3]  order by userName DESC
          select userId, userName from [users.4]  order by userName DESC
          select userId, userName from [users.5]  order by userName DESC
          select userId, userName from [users.6]  order by userName DESC
          select userId, userName from [users.7]  order by userName DESC
          select userId, userName from [users.8]  order by userName DESC
          select userId, userName from [users.9]  order by userName DESC
          select userId, userName from [users.a]  order by userName DESC
          select userId, userName from [users.b]  order by userName DESC
          select userId, userName from [users.c]  order by userName DESC
          select userId, userName from [users.d]  order by userName DESC
          select userId, userName from [users.e]  order by userName DESC
          select userId, userName from [users.f]  order by userName DESC
          select userId, userName from [users.0] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.1] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.2] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.3] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.4] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.5] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.6] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.7] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.8] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.9] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.a] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.b] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.c] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.d] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.e] WHERE userId='1212121' order by userName DESC
          select userId, userName from [users.f] WHERE userId='1212121' order by userName DESC

希望大家能对基础技术真正感兴趣，赶紧学习编译原理、antlr吧。

很抱歉没能提供详细原理说明，大家baidubaidu就都有了。

代码下载 http://files.cnblogs.com/files/aarond/SQLParser_Select.rar