mycat sql解析

mycat借助于druid提供的sql解析工具，把client端传入的sql语句解析成一棵AST语法树
AST语法树如下所示:

image.png

example1:
select * from table1 where c1 = 100 order by id desc, name asc limit 0, 10
解析后可以获得如下信息:
from table: table1
select list:[*]
where: c1 (Equality) 100
order by: id DESC
order by: name ASC
limit: offset = 0 count = 10

example2:
select c1, c2, c3 from table1 where c1 = 'v1' and c2 >= 100 order by id desc limit 0, 10
解析后可以获得如下信息:
from table: table1
select list:[c1, c2, c3]
where: c1 = 'v1' (BooleanAnd) c2 >= 100
order by: id DESC
limit: offset = 0 count = 10

另外还可以针对函数场景，多表join场景，带子查询场景，select-for-update等多种场景进行解析，功能非常强大，而且性能上似乎也比较快

使用之前需要在pom中增加对druid包的依赖

<dependency>
         <groupId>com.alibaba</groupId>
         <artifactId>druid</artifactId>
         <version>1.1.11</version>
 </dependency>

使用demo

public static void selectParse(String sql) {
        System.out.println("start parse sql:" + sql);
        MySqlStatementParser parser = new MySqlStatementParser(sql);
        SQLSelectStatement statement = (SQLSelectStatement) parser.parseStatement();
        SQLSelectQuery query = statement.getSelect().getQuery();
        if (query instanceof MySqlSelectQueryBlock) {
            MySqlSelectQueryBlock queryBlock = (MySqlSelectQueryBlock) query;
            System.out.println("from table:" + queryBlock.getFrom());
            System.out.println("select list:" + queryBlock.getSelectList());
            //System.out.println("where: " + queryBlock.getWhere());
            //System.out.println(queryBlock.getWhere().getClass().getName());
            SQLBinaryOpExpr where = (SQLBinaryOpExpr) queryBlock.getWhere();
            if (where != null) {
                System.out.println("where: " + where.getLeft() + " (" + where.getOperator() + ") " + where.getRight());
            }
            SQLOrderBy orderBy =  queryBlock.getOrderBy();
            if (orderBy != null) {
                for (SQLSelectOrderByItem item : queryBlock.getOrderBy().getItems()) {
                    System.out.println("order by:" + item.getExpr() + " " + item.getType());
                }
            }

            MySqlSelectQueryBlock.Limit limit = queryBlock.getLimit();
            if (limit != null) {
                System.out.println("limit:  offset = " + limit.getOffset() + " count = " + limit.getRowCount());

            }
        }
        System.out.println();

    }