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sql字段解析器的实现示例

程序员文章站 2022-06-18 14:29:51
目录用例: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,...

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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