解析HiveQL的ALTER TABLE ADD/REPLACE COLUMNS语句

阅读以下ALTER TABLE的ADD/REPLACE COLUMNS语句的语法，用C#编写解析函数，一个一个字符解析，所有关键字不区分大小写，一个或多个空格、Tab和换行的组合都可以是关键词之间的分隔，表名和字段名可能包含空格和Tab，语句中可以用`包裹表名和字段名，解析以下HiveQL语句在所有可能的参数组合下的所有参数信息，并存储到一个类的成员属性中，然后打印输出，如果语句符合以下ALTER TABLE的ADD/REPLACE COLUMNS语句的语法则函数返回true，否则返回false，同时需要考虑单行注释和多行注释的情况，同时要优化解析算法，以及编写所有可能语句类型的测试用例。
Add/Replace Columns

ALTER TABLE table_name [PARTITION partition_spec] – (Note: Hive 0.14.0 and later)
ADD|REPLACE COLUMNS (col_name data_type [COMMENT col_comment], …) [CASCADE|RESTRICT]
– (Note: Hive 1.1.0 and later)

ADD COLUMNS lets you add new columns to the end of the existing columns but before the partition columns. This is supported for Avro backed tables as well, for Hive 0.14 and later.

REPLACE COLUMNS removes all existing columns and adds the new set of columns. This can be done only for tables with a native SerDe (DynamicSerDe, MetadataTypedColumnsetSerDe, LazySimpleSerDe and ColumnarSerDe). Refer to Hive SerDe for more information. REPLACE COLUMNS can also be used to drop columns. For example, “ALTER TABLE test_change REPLACE COLUMNS (a int, b int);” will remove column ‘c’ from test_change’s schema.

The PARTITION clause is available in Hive 0.14.0 and later; see Upgrading Pre-Hive 0.13.0 Decimal Columns for usage.

The CASCADE|RESTRICT clause is available in Hive 1.1.0. ALTER TABLE ADD|REPLACE COLUMNS with CASCADE command changes the columns of a table’s metadata, and cascades the same change to all the partition metadata. RESTRICT is the default, limiting column changes only to table metadata.

ALTER TABLE ADD or REPLACE COLUMNS CASCADE will override the table partition’s column metadata regardless of the table or partition’s protection mode. Use with discretion.The column change command will only modify Hive’s metadata, and will not modify data. Users should make sure the actual data layout of the table/partition conforms with the metadata definition.

解析流程与解决方案

1. 语法分析：根据HiveQL语法规范，逐部分解析语句
2. 注释处理：支持单行(–)和多行(/* */)注释
3. 灵活分隔符：处理任意空白符组合（空格、Tab、换行）
4. 命名处理：支持反引号包裹的包含特殊字符的标识符
5. 状态跟踪：使用基于指针的解析方式逐个字符处理输入
6. 错误处理：快速失败机制，遇到错误立即终止解析

核心实现代码

using System;
using System.Collections.Generic;
using System.Text;

public enum CascadeOption {
    None, Cascade, Restrict }

public class ColumnInfo
{
   
    public string Name {
    get; set; }
    public string DataType {
    get; set; }
    public string Comment {
    get; set; }
}

public class AlterTableInfo
{
   
    public string TableName {
    get; set; }
    public string PartitionSpec {
    get; set; }
    public bool IsReplace {
    get; set; }
    public List<ColumnInfo> Columns {
    get; } = new List<ColumnInfo>();
    public CascadeOption CascadeOption {
    get; set; }

    public void Print()
    {
   
        Console.WriteLine($"Table: {
     TableName}");
        Console.WriteLine($"Operation: {
     (IsReplace ? "REPLACE" : "ADD")} COLUMNS");
        if (!string.IsNullOrEmpty(PartitionSpec))
            Console.WriteLine($"Partition: {
     PartitionSpec}");
        Console.WriteLine("Columns:");
        foreach (var col in Columns)
        {
   
            Console.WriteLine($"  {
     col.Name} {
     col.DataType}" + 
                (col.Comment != null ? $" COMMENT '{
     col.Comment}'" : ""));
        }
        Console.WriteLine($"Cascade Option: {
     CascadeOption}");
    }
}

public class HiveAlterTableParser
{
   
    private string _input;
    private int _pos;
    private AlterTableInfo _result;
    private bool _hasError;

    public bool TryParse(string sql, out AlterTableInfo result)
    {
   
        _input = sql;
        _pos = 0;
        _result = new AlterTableInfo();
        _hasError = false;

        try
        {
   
            ParseAlterTable();
            result = _hasError ? null : _result;
            return !_hasError;
        }
        catch
        {
   
            result = null;
            return false;
        }
    }

    private void ParseAlterTable()
    {
   
        SkipWhitespaceAndComments();
        if (!MatchKeyword("ALTER")) Fail();