手写一个简单的ElasticSearch SQL转换器(一)

一.前言

之前有个需求，是使ElasticSearch支持使用SQL进行简单查询，较新版本的ES已经支持该特性(不过貌似还是实验性质的？) ，而且git上也有elasticsearch-sql

插件，之所以决定手写一个，主要有两点原因：

1. 目前用的ES版本较老

2. elasticsearch-sql虽好，但比较复杂，代码也不易维护

3. 练练手

 二.技术选型

目前主流软件中通常使用ANTLR做词法语法分析，诸如著名的Hibernate，Spark，Hive等项目，之前因为工作原因也有所接触，不过如果只是解析标准SQL的话，

其实还有更好的选择，如使用Hibernate或阿里巴巴的数据库Druid(Druid采用了手写词法语法分析器的方案，这种方式当然比自动ANTLR生成的解析器性能高得多), 这里

我选择了第二种方案。

开始之前先看下我们可以通过Druid拿到的SQL语言的抽象语法树：

图片：https://www.jianshu.com/p/437aa22ea3ca

三.技术实现

首先我们创建一个SqlParser类，主流程都在parse方法中，该方法负责将一个SQL字符串解析(顺便说一句，Druid支持多种SQL方言，这里我选择了MySQL)，

并返回SearchSourceBuilder对象，这是一个ElasticSearch提供的DSL构建器，以该对象作为参数，ES client端即可发起对ES 服务端搜索请求。

 /**
  *
  * @author fred
  *
  */
 public class SqlParser {
     private final static String dbType = JdbcConstants.MYSQL;
     private final static Logger logger = LoggerFactory.getLogger(SqlParser.class);
     private SearchSourceBuilder builder;

     public SqlParser(SearchSourceBuilder builder) {
         this.builder = builder;
     }
     /**
      * 将SQL解析为ES查询
      */
     public SearchSourceBuilder parse(String sql) throws Exception {
         if (Objects.isNull(sql)) {
             throw new IllegalArgumentException("输入语句不得为空");
         }
         sql = sql.trim().toLowerCase();
         List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, dbType);
         if (Objects.isNull(stmtList) || stmtList.size() != 1) {
             throw new IllegalArgumentException("必须输入一句查询语句");
         }
         // 使用Parser解析生成AST
         SQLStatement stmt = stmtList.get(0);
         if (!(stmt instanceof SQLSelectStatement)) {
             throw new IllegalArgumentException("输入语句须为Select语句");
         }
         SQLSelectStatement sqlSelectStatement = (SQLSelectStatement) stmt;
         SQLSelectQuery sqlSelectQuery = sqlSelectStatement.getSelect().getQuery();
         SQLSelectQueryBlock sqlSelectQueryBlock = (SQLSelectQueryBlock) sqlSelectQuery;

         SQLExpr whereExpr = sqlSelectQueryBlock.getWhere();

         // 生成ES查询条件
         BoolQueryBuilder bridge = QueryBuilders.boolQuery();
         bridge.must();

         QueryBuilder whereBuilder = whereHelper(whereExpr); // 处理where
         bridge.must(whereBuilder);
         SQLOrderBy orderByExpr = sqlSelectQueryBlock.getOrderBy(); // 处理order by
         if (Objects.nonNull(orderByExpr)) {
             orderByHelper(orderByExpr, bridge);
         }
         builder.query(bridge);
         return builder;
     }

主流程很简单，拿到SQL字符串后，直接通过Druid API将其转换为抽象语法树，我们要求输入语句必须为Select语句。接下来是对where语句和order by语句的处理，

目前的难点其实主要在于如何将where语句映射到ES查询中。

先从简单的看起，如何处理order by呢？SQL语句中 order by显然可以允许用户根据多字段排序，所以排序字段肯定是一个List<排序字段>，我们要做的就是将这个List映射到

SearchSourceBuilder对象中。见下面代码：

     /**
      * 处理所有order by字段
      *
      * @param orderByExpr
      */
     private void orderByHelper(SQLOrderBy orderByExpr, BoolQueryBuilder bridge) {
         List<SQLSelectOrderByItem> orderByList = orderByExpr.getItems(); // 待排序的列
         for (SQLSelectOrderByItem sqlSelectOrderByItem : orderByList) {
             if (sqlSelectOrderByItem.getType() == null) {
                 sqlSelectOrderByItem.setType(SQLOrderingSpecification.ASC); // 默认升序
             }
             String orderByColumn = sqlSelectOrderByItem.getExpr().toString();
             builder.sort(orderByColumn,
                     sqlSelectOrderByItem.getType().equals(SQLOrderingSpecification.ASC) ? SortOrder.ASC
                             : SortOrder.DESC);
         }
     }

通过Druid的API，我们很容易拿到了SQL语句中所有的排序字段，我们逐个遍历这些字段，拿到排序的列名字面量和顺序，传递给SearchSourceBuilder的sort方法，需注意的

是， 如果原始SQL中没有指定字段是顺序，我们默认升序。

接下来我们处理稍微有点麻烦的where语句，因为SQL语句被解析成了语法树，很自然的我们想到使用递归方式进行处理。 而通常在处理递归问题的时候，

我习惯于从递归的base case开始考虑，where语句中的运算符根据Druid API中的定义主要分为以下三种：

1. 简单二元运算符：包括逻辑处理，如and, or 和大部分关系运算(后续会详细讲)

2. between或not between运算符：我们可以简单的将其映射成ES中的Range Query

3. in, not in 运算符: 可以简单的映射成ES中的Term Query

通过Druid，我们可以很方便的获取每种运算中的运算符与操作数

 /**
      * 递归遍历“where”子树
      *
      * @return
      */
     private QueryBuilder whereHelper(SQLExpr expr) throws Exception {
         if (Objects.isNull(expr)) {
             throw new NullPointerException("节点不能为空!");
         }
         BoolQueryBuilder bridge = QueryBuilders.boolQuery();
         if (expr instanceof SQLBinaryOpExpr) { // 二元运算
             SQLBinaryOperator operator = ((SQLBinaryOpExpr) expr).getOperator(); // 获取运算符
             if (operator.isLogical()) { // and,or,xor
                 return handleLogicalExpr(expr);
             } else if (operator.isRelational()) { // 具体的运算,位于叶子节点
                 return handleRelationalExpr(expr);
             }
         } else if (expr instanceof SQLBetweenExpr) { // between运算
             SQLBetweenExpr between = ((SQLBetweenExpr) expr);
             boolean isNotBetween = between.isNot(); // between or not between ?
             String testExpr = between.testExpr.toString();
             String fromStr = formatSQLValue(between.beginExpr.toString());
             String toStr = formatSQLValue(between.endExpr.toString());
             if (isNotBetween) {
                 bridge.must(QueryBuilders.rangeQuery(testExpr).lt(fromStr).gt(toStr));
             } else {
                 bridge.must(QueryBuilders.rangeQuery(testExpr).gte(fromStr).lte(toStr));
             }
             return bridge;
         } else if (expr instanceof SQLInListExpr) { // SQL的 in语句，ES中对应的是terms
             SQLInListExpr siExpr = (SQLInListExpr) expr;
             boolean isNotIn = siExpr.isNot(); // in or not in?
             String leftSide = siExpr.getExpr().toString();
             List<SQLExpr> inSQLList = siExpr.getTargetList();
             List<String> inList = new ArrayList<>();
             for (SQLExpr in : inSQLList) {
                 String str = formatSQLValue(in.toString());
                 inList.add(str);
             }
             if (isNotIn) {
                 bridge.mustNot(QueryBuilders.termsQuery(leftSide, inList));
             } else {
                 bridge.must(QueryBuilders.termsQuery(leftSide, inList));
             }
             return bridge;
         }
         return bridge;
     }

上述第一种情况比较复杂，首先我们先看看运算符是逻辑运算的情况：

如下面的代码所示，如果运算符是逻辑运算符，我们需要对左右操作数分别递归，然后根据运算符类型归并结果：or可以映射成ES 中的Should，而and则映射成Must.

    /**
     * 逻辑运算符，目前支持and,or
     *
     * @return
     * @throws Exception
     */
    private QueryBuilder handleLogicalExpr(SQLExpr expr) throws Exception {
        BoolQueryBuilder bridge = QueryBuilders.boolQuery();
        SQLBinaryOperator operator = ((SQLBinaryOpExpr) expr).getOperator(); // 获取运算符
        SQLExpr leftExpr = ((SQLBinaryOpExpr) expr).getLeft();
        SQLExpr rightExpr = ((SQLBinaryOpExpr) expr).getRight();

        // 分别递归左右子树，再根据逻辑运算符将结果归并
        QueryBuilder leftBridge = whereHelper(leftExpr);
        QueryBuilder rightBridge = whereHelper(rightExpr);
        if (operator.equals(SQLBinaryOperator.BooleanAnd)) {
            bridge.must(leftBridge).must(rightBridge);
        } else if (operator.equals(SQLBinaryOperator.BooleanOr)) {
            bridge.should(leftBridge).should(rightBridge);
        }
        return bridge;
    }

下面来讨论下第一种情况中，如果运算符是关系运算符的情况，我们知道，SQL中的关系运算主要就是一些比较运算符，诸如大于，小于，等于，Like等，这里我还加上了

正则搜索(不过貌似性能比较差，ES对正则搜索的限制颇多，不太建议使用)。

/**
     * 大于小于等于正则
     *
     * @param expr
     * @return
     */
    private QueryBuilder handleRelationalExpr(SQLExpr expr) {
        SQLExpr leftExpr = ((SQLBinaryOpExpr) expr).getLeft();
        if (Objects.isNull(leftExpr)) {
            throw new NullPointerException("表达式左侧不得为空");
        }
        String leftExprStr = leftExpr.toString();
        String rightExprStr = formatSQLValue(((SQLBinaryOpExpr) expr).getRight().toString()); // TODO:表达式右侧可以后续支持方法调用
        SQLBinaryOperator operator = ((SQLBinaryOpExpr) expr).getOperator(); // 获取运算符
        QueryBuilder queryBuilder;
        switch (operator) {
        case GreaterThanOrEqual:
            queryBuilder = QueryBuilders.rangeQuery(leftExprStr).gte(rightExprStr);
            break;
        case LessThanOrEqual:
            queryBuilder = QueryBuilders.rangeQuery(leftExprStr).lte(rightExprStr);
            break;
        case Equality:
            queryBuilder = QueryBuilders.boolQuery();
            TermQueryBuilder eqCond = QueryBuilders.termQuery(leftExprStr, rightExprStr);
            ((BoolQueryBuilder) queryBuilder).must(eqCond);
            break;
        case GreaterThan:
            queryBuilder = QueryBuilders.rangeQuery(leftExprStr).gt(rightExprStr);
            break;
        case LessThan:
            queryBuilder = QueryBuilders.rangeQuery(leftExprStr).lt(rightExprStr);
            break;
        case NotEqual:
            queryBuilder = QueryBuilders.boolQuery();
            TermQueryBuilder notEqCond = QueryBuilders.termQuery(leftExprStr, rightExprStr);
            ((BoolQueryBuilder) queryBuilder).mustNot(notEqCond);
            break;
        case RegExp: // 对应到ES中的正则查询
            queryBuilder = QueryBuilders.boolQuery();
            RegexpQueryBuilder regCond = QueryBuilders.regexpQuery(leftExprStr, rightExprStr);
            ((BoolQueryBuilder) queryBuilder).mustNot(regCond);
            break;
        case NotRegExp:
            queryBuilder = QueryBuilders.boolQuery();
            RegexpQueryBuilder notRegCond = QueryBuilders.regexpQuery(leftExprStr, rightExprStr);
            ((BoolQueryBuilder) queryBuilder).mustNot(notRegCond);
            break;
        case Like:
            queryBuilder = QueryBuilders.boolQuery();
            MatchPhraseQueryBuilder likeCond = QueryBuilders.matchPhraseQuery(leftExprStr,
                    rightExprStr.replace("%", ""));
            ((BoolQueryBuilder) queryBuilder).must(likeCond);
            break;
        case NotLike:
            queryBuilder = QueryBuilders.boolQuery();
            MatchPhraseQueryBuilder notLikeCond = QueryBuilders.matchPhraseQuery(leftExprStr,
                    rightExprStr.replace("%", ""));
            ((BoolQueryBuilder) queryBuilder).mustNot(notLikeCond);
            break;
        default:
            throw new IllegalArgumentException("暂不支持该运算符!" + operator.toString());
        }
        return queryBuilder;
    }

到这里我们就完成了SQL转ES DSL的功能了(其实只是简单查询的转换)，下面我们写几个Junit测试一下吧：

首先是简单的比较运算：

public void normalSQLTest() {
        String sql = "select * from test where time>= 1";
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
         try {
             searchSourceBuilder = new SqlParser(searchSourceBuilder).parse(sql);
        } catch (Exception e) {
            e.printStackTrace();
        }
         System.out.println(searchSourceBuilder);
         SearchSourceBuilder builderToCompare = new SearchSourceBuilder();
         QueryBuilder whereBuilder = QueryBuilders.rangeQuery("time").gte("");
         BoolQueryBuilder briage = QueryBuilders.boolQuery();
         briage.must();
         briage.must(whereBuilder);
         builderToCompare.query(briage);
         assertEquals(searchSourceBuilder,builderToCompare);
    }

下面是输出的ES 查询语句：

{
  "query" : {
    "bool" : {
      "must" : [
        {
          "range" : {
            "time" : {
              "from" : "",
              "to" : null,
              "include_lower" : true,
              "include_upper" : true,
              "boost" : 1.0
            }
          }
        }
      ],
      "disable_coord" : false,
      "adjust_pure_negative" : true,
      "boost" : 1.0
    }
  }
}

再来个带排序的：

    @Test
    public void normalSQLWithOrderByTest() {
        String sql = "select * from test where time>= 1 order by time desc";
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
         try {
             searchSourceBuilder = new SqlParser(searchSourceBuilder).parse(sql);
        } catch (Exception e) {
            e.printStackTrace();
        }
         System.out.println(searchSourceBuilder);
         SearchSourceBuilder builderToCompare = new SearchSourceBuilder();
         QueryBuilder whereBuilder = QueryBuilders.rangeQuery("time").gte("1");
         BoolQueryBuilder briage = QueryBuilders.boolQuery();
         briage.must();
         briage.must(whereBuilder);
         builderToCompare.sort("time",SortOrder.DESC);
         builderToCompare.query(briage);
         assertEquals(searchSourceBuilder,builderToCompare);
    }

between, in这些没什么区别，就不贴代码了，最后看看稍微复杂点儿，带逻辑运算的查询：

@Test
    public void sqlLogicTest() {
        String sql = "select * from test where raw_log not like"+"'%aaa' && b=1 or c=0";
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
         try {
             searchSourceBuilder = new SqlParser(searchSourceBuilder).parse(sql);
        } catch (Exception e) {
            e.printStackTrace();
        }
         System.out.println(searchSourceBuilder);
         SearchSourceBuilder builderToCompare = new SearchSourceBuilder();
         QueryBuilder builder =QueryBuilders.matchPhraseQuery("raw_log","aaa"); 

         BoolQueryBuilder briage1 = QueryBuilders.boolQuery();//raw log not like
         briage1.mustNot(builder);  

         BoolQueryBuilder briage2 = QueryBuilders.boolQuery();  //b=1
         briage2.must(QueryBuilders.termQuery("b","1"));

         BoolQueryBuilder briage3 = QueryBuilders.boolQuery();   // not like and b=1
         briage3.must(briage1).must(briage2);

         BoolQueryBuilder briage4 = QueryBuilders.boolQuery();    //c =0
         briage4.must(QueryBuilders.termQuery("c","0"));

         BoolQueryBuilder briage5 = QueryBuilders.boolQuery();  // not like and b =1 or c =0
         briage5.should(briage3).should(briage4);

         BoolQueryBuilder briage6 = QueryBuilders.boolQuery();
         briage6.must();
         briage6.must(briage5);
         builderToCompare.query(briage6);
         assertEquals(searchSourceBuilder,builderToCompare);
    }

下面是生成的查询语句：

{
  "query" : {
    "bool" : {
      "must" : [
        {
          "bool" : {
            "should" : [
              {
                "bool" : {
                  "must" : [
                    {
                      "bool" : {
                        "must_not" : [
                          {
                            "match_phrase" : {
                              "raw_log" : {
                                "query" : "aaa",
                                "slop" : 0,
                                "boost" : 1.0
                              }
                            }
                          }
                        ],
                        "disable_coord" : false,
                        "adjust_pure_negative" : true,
                        "boost" : 1.0
                      }
                    },
                    {
                      "bool" : {
                        "must" : [
                          {
                            "term" : {
                              "b" : {
                                "value" : "1",
                                "boost" : 1.0
                              }
                            }
                          }
                        ],
                        "disable_coord" : false,
                        "adjust_pure_negative" : true,
                        "boost" : 1.0
                      }
                    }
                  ],
                  "disable_coord" : false,
                  "adjust_pure_negative" : true,
                  "boost" : 1.0
                }
              },
              {
                "bool" : {
                  "must" : [
                    {
                      "term" : {
                        "c" : {
                          "value" : "0",
                          "boost" : 1.0
                        }
                      }
                    }
                  ],
                  "disable_coord" : false,
                  "adjust_pure_negative" : true,
                  "boost" : 1.0
                }
              }
            ],
            "disable_coord" : false,
            "adjust_pure_negative" : true,
            "boost" : 1.0
          }
        }
      ],
      "disable_coord" : false,
      "adjust_pure_negative" : true,
      "boost" : 1.0
    }
  }
}

四.总结

本篇文章主要讲述了如何使用Druid实现SQL语句转换ES DSL进行搜索的功能，后续文章中会陆续完善这个功能，实现诸如聚合查询，分页查询等功能。