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[SQL Server] sql字段解析器的实现示例

数据库 数据库 发布于:2021-08-03 13:28 | 阅读数:560 | 评论:0

目录

  • 1. 解题思路
  • 2. 具体解析实现
  • 3. 单元测试
用例:有一段sql语句,我们需要从中截取出所有字段部分,以便进行后续的类型推断或者别名字段抽取定义,请给出此解析方法。
想来很简单吧,因为 sql 中的字段列表,使用方式有限,比如 a as b, a, a b...

1. 解题思路

如果不想做复杂处理,最容易想到的,就是直接用某个特征做分割即可。比如,先截取出 字段列表部分,然后再用逗号',' 分割,就可以得到一个个的字段了。然后再要细分,其实只需要用 as 进行分割就可以了。
看起来好像可行,但是存在许多漏洞,首先,这里面有太多的假设:各种截取部分要求必须符合要求,必须没有多余的逗号,必须要有as 等等。这明显不符合要求了。
其二,我们可以换一种转换方式。比如先截取到field部分,然后先以 as 分割,再以逗号分割,然后取最后一个词作为field。
看起来好像更差了,截取到哪里已经完全不知道了。即原文已经被破坏殆尽,而且同样要求要有 as 转换标签,而且对于函数觊觎有 as 的场景,就完全错误了。
其三,最好还是自行一个个单词地解析,field 字段无外乎几种情况,1. 普通字段如 select a; 2. 带as的普通字段如 select a as b; 3. 带函数的字段如 select coalesce(a, b); 4. 带函数且带as的字段如 select coalesce(a, b) ab; 5. 函数内带as的字段如 select cast(a as string) b; ...   我们只需依次枚举对应的情况,就可以将字段解析出来了。
看起来是个不错的想法。但是具体实现如何?

2. 具体解析实现

主要分两个部分,1. 需要定义一个解析后的结果数据结构,以便清晰描述字段信息; 2. 分词解析sql并以结构体返回;
我们先来看看整个算法核心:
/**
 * 功能描述: 简单sql字段解析器
 *
 *    样例如1:
 *      select COALESCE(t1.xno, t2.xno, t3.xno) as xno,
 *       case when t1.no is not null then 1 else null end as xxk001,
 *       case when t2.no is not null then 1 else null end as xxk200,
 *       case when t3.xno is not null then 1 else null end as xx3200
 *       from xxk001 t1
 *         full join xxkj100 t2 on t1.xno = t2.xno
 *         full join xxkj200 t3 on t1.xno = t3.xno;
 *
 *    样例如2:
 *      select cast(a as string) as b from ccc;
 *
 *    样例如3:
 *      with a as(select cus,x1 from b1), b as (select cus,x2 from b2)
 *        select a.cus as a_cus from a join b on a.cus=b.cus where xxx;
 *
 *    样例如4:
 *     select a.xno,b.xx from a_tb as a join b_tb as b on a.id = b.id
 *
 *    样例如5:
 *      select cast  \t(a as string) a_str, cc (a as double) a_double from x
 *
 */
public class SimpleSqlFieldParser {
  /**
   * 解析一段次标签sql 中的字段列表
   *
   * @param sql 原始sql, 需如 select xx from xxx join ... 格式
   * @return 字段列表
   */
  public static List<SelectFieldClauseDescriptor> parse(String sql) {
    String columnPart = adaptFieldPartSql(sql);
    int deep = 0;
    List<StringBuilder> fieldTokenSwap = new ArrayList<>();
    StringBuilder currentTokenBuilder = new StringBuilder();
    List<SelectFieldClauseDescriptor> fieldList = new ArrayList<>();
    fieldTokenSwap.add(currentTokenBuilder);
    int len = columnPart.length();
    char[] columnPartChars = columnPart.toCharArray();
    for(int i = 0; i < len; i++) {
      // 空格忽略,换行忽略,tab忽略
      // 字符串相接
      // 左(号入栈,++deep;
      // 右)号出栈,--deep;
      // deep>0 忽略所有其他直接拼接
      // as 则取下一个值为fieldName
      // case 则直接取到end为止;
      //,号则重置token,构建结果集
      char currentChar = columnPartChars[i];
      switch (currentChar) {
        case '(':
          ++deep;
          currentTokenBuilder.append(currentChar);
          break;
        case ')':
          --deep;
          currentTokenBuilder.append(currentChar);
          break;
        case ',':
          if(deep == 0) {
            addNewField(fieldList, fieldTokenSwap, true);
            fieldTokenSwap = new ArrayList<>();
            currentTokenBuilder = new StringBuilder();
            fieldTokenSwap.add(currentTokenBuilder);
            break;
          }
          currentTokenBuilder.append(currentChar);
          break;
        case ' ':
        case '\t':
        case '\r':
        case '\n':
          if(deep > 0) {
            currentTokenBuilder.append(currentChar);
            continue;
          }
          if(currentTokenBuilder.length() == 0) {
            continue;
          }
          // original_name as   --> alias
          if(i + 1 < len) {
            int j = i + 1;
            // 收集连续的空格
            StringBuilder spaceHolder = new StringBuilder();
            boolean isNextLeftBracket = false;
            do {
              char nextChar = columnPart.charAt(j++);
              if(nextChar == ' ' || nextChar == '\t'
                  || nextChar == '\r' || nextChar == '\n') {
                spaceHolder.append(nextChar);
                continue;
              }
              if(nextChar == '(') {
                isNextLeftBracket = true;
              }
              break;
            } while (j < len);
            if(isNextLeftBracket) {
              currentTokenBuilder.append(currentChar);
            }
            if(spaceHolder.length() > 0) {
              currentTokenBuilder.append(spaceHolder);
              i += spaceHolder.length();
            }
            if(isNextLeftBracket) {
              // continue next for, function begin
              continue;
            }
          }
          if(fieldTokenSwap.size() == 1) {
            if(fieldTokenSwap.get(0).toString().equalsIgnoreCase("case")) {
              String caseWhenPart = CommonUtil.readSplitWord(
                  columnPartChars, i, " ", "end");
              currentTokenBuilder.append(caseWhenPart);
              if(caseWhenPart.length() <= 0) {
                throw new BizException("语法错误,未找到case..when的结束符");
              }
              i += caseWhenPart.length();
            }
          }
          addNewField(fieldList, fieldTokenSwap, false);
          currentTokenBuilder = new StringBuilder();
          fieldTokenSwap.add(currentTokenBuilder);
          break;
          // 空格忽略
        default:
          currentTokenBuilder.append(currentChar);
          break;
      }
    }
    // 处理剩余尚未存储的字段信息
    addNewField(fieldList, fieldTokenSwap, true);
    return fieldList;
  }
  /**
   * 新增一个字段描述
   *
   * @param fieldList 字段容器
   * @param fieldTokenSwap 候选词
   */
  private static void addNewField(List<SelectFieldClauseDescriptor> fieldList,
                  List<StringBuilder> fieldTokenSwap,
                  boolean forceAdd) {
    int ts = fieldTokenSwap.size();
    if(ts == 1 && forceAdd) {
      // db.original_name,
      String fieldName = fieldTokenSwap.get(0).toString();
      String alias = fieldName;
      if(fieldName.contains(".")) {
        alias = fieldName.substring(fieldName.lastIndexOf('.') + 1);
      }
      fieldList.add(new SelectFieldClauseDescriptor(fieldName, alias));
      return;
    }
    if(ts < 2) {
      return;
    }
    if(ts == 2) {
      // original_name alias,
      if(fieldTokenSwap.get(1).toString().equalsIgnoreCase("as")) {
        return;
      }
      fieldList.add(new SelectFieldClauseDescriptor(
          fieldTokenSwap.get(0).toString(),
          fieldTokenSwap.get(1).toString()));
    }
    else if(ts == 3) {
      // original_name as alias,
      fieldList.add(new SelectFieldClauseDescriptor(
          fieldTokenSwap.get(0).toString(),
          fieldTokenSwap.get(2).toString()));
    }
    else {
      throw new BizException("字段语法解析错误,超过3个以字段描述信息:" + ts);
    }
  }
  // 截取适配 field 字段信息部分
  private static String adaptFieldPartSql(String fullSql) {
    int start = fullSql.lastIndexOf("select ");
    int end = fullSql.lastIndexOf(" from");
    String columnPart = fullSql.substring(start + "select ".length(), end);
    return columnPart.trim();
  }
}
应该说是比较简单的,一个for, 一个 switch ,就搞定了。其他的,更多的是逻辑判定。
下面我们来看看字段描述类的写法,其实就是两个字段,源字段和别名。
/**
 * 功能描述: sql字段描述 select 字段描述类
 *
 */
public class SelectFieldClauseDescriptor {
  private String fieldName;
  private String alias;
  public SelectFieldClauseDescriptor(String fieldName, String alias) {
    this.fieldName = fieldName;
    this.alias = alias;
  }
  public String getFieldName() {
    return fieldName;
  }
  public String getAlias() {
    return alias;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    SelectFieldClauseDescriptor that = (SelectFieldClauseDescriptor) o;
    return Objects.equals(fieldName, that.fieldName) &&
        Objects.equals(alias, that.alias);
  }
  @Override
  public int hashCode() {
    return Objects.hash(fieldName, alias);
  }
  @Override
  public String toString() {
    return "SelectFieldClauseDescriptor{" +
        "fieldName='" + fieldName + '\'' +
        ", alias='" + alias + '\'' +
        '}';
  }
}
它存在的意义,仅仅是为了使用方更方便取值,以为更进一步的解析提供了依据。

3. 单元测试

其实像写这种工具类,单元测试最是方便简单。因为最初的结果,我们早已预料,以测试驱动开发最合适不过了。而且,基本上一出现不符合预期的值时,很快速就定位问题了。
/**
 * 功能描述: sql字段解析器测试
 **/
public class SimpleSqlFieldParserTest {
  @Test
  public void testParse() {
    String sql;
    List<SelectFieldClauseDescriptor> parsedFieldList;
    sql = "select COALESCE(t1.xno, t2.xno, t3.xno) as xno,\n" +
        "   case when t1.xno is not null then 1 else null end as xxk001,\n" +
        "   case when t2.xno is not null then 1 else null end as xxk200,\n" +
        "   case when t3.xno is not null then 1 else null end as xx3200\n" +
        "   from xxk001 t1\n" +
        "   full join xxkj100 t2 on t1.xno = t2.xno\n" +
        "   full join xxkj200 t3 on t1.xno = t3.xno;";
    parsedFieldList = SimpleSqlFieldParser.parse(sql);
    System.out.println("result:");
    parsedFieldList.forEach(System.out::println);
    Assert.assertEquals("字段个数解析不正确",
        4, parsedFieldList.size());
    Assert.assertEquals("字段别名解析不正确",
        "xno", parsedFieldList.get(0).getAlias());
    Assert.assertEquals("字段别名解析不正确",
        "xx3200", parsedFieldList.get(3).getAlias());
    sql = "select cast(a as string) as b from ccc;";
    parsedFieldList = SimpleSqlFieldParser.parse(sql);
    System.out.println("result:");
    parsedFieldList.forEach(System.out::println);
    Assert.assertEquals("字段个数解析不正确",
        1, parsedFieldList.size());
    Assert.assertEquals("字段别名解析不正确",
        "b", parsedFieldList.get(0).getAlias());
    sql = "with a as(select cus,x1 from b1), b as (select cus,x2 from b2)\n" +
        "  select a.cus as a_cus, cast(a \nas string) as a_cus2, " +
        "b.x2 b2 from a join b on a.cus=b.cus where xxx;";
    parsedFieldList = SimpleSqlFieldParser.parse(sql);
    System.out.println("result:");
    parsedFieldList.forEach(System.out::println);
    Assert.assertEquals("字段个数解析不正确",
        3, parsedFieldList.size());
    Assert.assertEquals("字段别名解析不正确",
        "a_cus", parsedFieldList.get(0).getAlias());
    Assert.assertEquals("字段别名解析不正确",
        "b2", parsedFieldList.get(2).getAlias());
    sql = "select a.xno,b.xx,qqq from a_tb as a join b_tb as b on a.id = b.id";
    parsedFieldList = SimpleSqlFieldParser.parse(sql);
    System.out.println("result:");
    parsedFieldList.forEach(System.out::println);
    Assert.assertEquals("字段个数解析不正确",
        3, parsedFieldList.size());
    Assert.assertEquals("字段别名解析不正确",
        "xno", parsedFieldList.get(0).getAlias());
    Assert.assertEquals("字段别名解析不正确",
        "qqq", parsedFieldList.get(2).getAlias());
    sql = "select cast (a.a_int as string) a_str, b.xx, coalesce  \n( a, b, c) qqq from a_tb as a join b_tb as b on a.id = b.id";
    parsedFieldList = SimpleSqlFieldParser.parse(sql);
    System.out.println("result:");
    parsedFieldList.forEach(System.out::println);
    Assert.assertEquals("字段个数解析不正确",
        3, parsedFieldList.size());
    Assert.assertEquals("字段别名解析不正确",
        "a_str", parsedFieldList.get(0).getAlias());
    Assert.assertEquals("字段原始名解析不正确",
        "cast (a.a_int as string)", parsedFieldList.get(0).getFieldName());
    Assert.assertEquals("字段别名解析不正确",
        "qqq", parsedFieldList.get(2).getAlias());
    Assert.assertEquals("字段原始名解析不正确",
        "coalesce  \n( a, b, c)", parsedFieldList.get(2).getFieldName());
  }
}
至此,一个简单的字段解析器完成。小工具,供参考!

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