如何给MySQL添加自定义语法的方法示例

create table t1 (
  id int primary key,
  name varchar(100)
) global_partition by hash(id) partitions 10; //global_partition by为新增语法，global_partition为新增token

sql/lex.h //token
sql/parse_tree_nodes.cc
sql/parse_tree_nodes.h
sql/parse_tree_partitions.cc
sql/parse_tree_partitions.h
sql/parser_yystype.h
sql/sql_yacc.yy

static const SYMBOL symbols[] = {
    /*
     Insert new SQL keywords after that commentary (by alphabetical order):
    */
    //省略部分代码
    {SYM("GLOBAL_PARTITION", GLOBAL_PARTITION_SYM)}, //注意按照字典序进行添加。
    //省略部分代码
};
  

%token<lexer.keyword> GLOBAL_PARTITION_SYM 1309            /* seancheer */  //### 声明上一步添加的token，声明了才可以使用，编号1309选择一个未使用的就行
%type <global_partition_clause> global_partition_clause //### 声明新增加的数据结构，后面会介绍

create_table_stmt:
          CREATE opt_temporary TABLE_SYM opt_if_not_exists table_ident
          '(' table_element_list ')' opt_create_table_options_etc //最后一个标记在YYSTYPE中对应的是create_table_tail， 后面会介绍
          {
            $$= NEW_PTN PT_create_table_stmt(YYMEM_ROOT, $1, $2, $4, $5,
                                             $7,
                                             $9.opt_create_table_options,
                                             $9.opt_partitioning,
                                             $9.opt_global_partitioning, //### 赋值给对应参数，该构造函数需要新增，后面会介绍
                                             $9.on_duplicate,
                                             $9.opt_query_expression);
          }
        | CREATE opt_temporary TABLE_SYM opt_if_not_exists table_ident
          opt_create_table_options_etc
          {
            $$= NEW_PTN PT_create_table_stmt(YYMEM_ROOT, $1, $2, $4, $5,
                                             NULL,
                                             $6.opt_create_table_options,
                                             $6.opt_partitioning,
                                             $6.opt_global_partitioning, //### 赋值给对应参数，该构造函数需要新增，后面会介绍
                                             $6.on_duplicate,
                                             $6.opt_query_expression);
//partition相关的语法                                             
opt_create_partitioning_etc:
          partition_clause opt_duplicate_as_qe //这里是原生的partition表语法
          {
            $$= $2;
            $$.opt_partitioning= $1;
          }
        | global_partition_clause opt_duplicate_as_qe //### 此处是新增的global_partition语法，
          {
            $$= $2;
            $$.opt_global_partitioning= $1;
          }
        | opt_duplicate_as_qe
        ;

//### 下面为重点，新增的global_partition语法，可以看到，用到了新增的token
global_partition_clause:
          GLOBAL_PARTITION_SYM BY part_type_def opt_num_parts
          {
            $$= NEW_PTN PT_global_partition($3, @4, $4);
          }
        ;

union YYSTYPE {
  PT_sub_partition *opt_sub_part;
  PT_part_type_def *part_type_def;
  PT_partition *partition_clause;
  PT_global_partition *global_partition_clause; //新加数据结构
  
  struct {
    Mem_root_array<PT_create_table_option *> *opt_create_table_options;
    PT_partition *opt_partitioning;
    PT_global_partition *opt_global_partitioning; //同时注意添加到create_table_tail里面，因为create table语法会有该操作
    On_duplicate on_duplicate;
    PT_query_primary *opt_query_expression;
  } create_table_tail;
};
static_assert(sizeof(YYSTYPE) <= 40, "YYSTYPE is too big"); //因为struct里面添加了一个成员变量，所以该union需要的空间也会变大，因此注意修改这一行

/**
新增数据结构
*/
class PT_global_partition : public Parse_tree_node {
    typedef Parse_tree_node super;

    PT_part_type_def *const part_type_def;
    const POS part_defs_pos;
    uint num_parts;
public:
    partition_info part_info;
public:
    PT_global_partition(PT_part_type_def *part_type_def, const POS &part_defs_pos,
                        uint opt_num_parts)
            : part_type_def(part_type_def),
              part_defs_pos(part_defs_pos),
              num_parts(opt_num_parts) {}
    bool contextualize(Parse_context *pc) override;
};

//模仿其原生的实现方式即可
bool PT_global_partition::contextualize(Parse_context *pc) {
    if (super::contextualize(pc)) return true;

    Partition_parse_context part_pc(pc->thd, &part_info, false);
    if (part_type_def->contextualize(&part_pc)) return true;

    if (part_info.part_type != partition_type::HASH) {
        //only support hash partition for shard key
        my_error(ER_PARTITIONS_MUST_BE_DEFINED_ERROR, MYF(0), "NOT HASH");
        return true;
    }

    uint count_curr_parts = part_info.partitions.elements;

    if (part_info.num_parts != 0) {
        if (part_info.num_parts != count_curr_parts) {
            error(&part_pc, part_defs_pos,
                  ER_THD(pc->thd, ER_PARTITION_WRONG_NO_PART_ERROR));
            return true;
        }
    } else if (count_curr_parts > 0)
        part_info.num_parts = count_curr_parts;
    return false;
}

class PT_create_table_stmt final : public PT_table_ddl_stmt_base {
  PT_partition *opt_partitioning;
  PT_global_partition *opt_global_partitioning; //添加成员变量
  PT_create_table_stmt(
    MEM_ROOT *mem_root, PT_hint_list *opt_hints, bool is_temporary,
    bool only_if_not_exists, Table_ident *table_name,
    const Mem_root_array<PT_table_element *> *opt_table_element_list,
    const Mem_root_array<PT_create_table_option *> *opt_create_table_options,
    PT_partition *opt_partitioning,
    PT_global_partition *opt_global_partitioning, On_duplicate on_duplicate,
    PT_query_primary *opt_query_expression)
    : PT_table_ddl_stmt_base(mem_root),
  m_opt_hints(opt_hints),
  is_temporary(is_temporary),
  only_if_not_exists(only_if_not_exists),
  table_name(table_name),
  opt_table_element_list(opt_table_element_list),
  opt_create_table_options(opt_create_table_options),
  opt_partitioning(opt_partitioning),
  opt_global_partitioning(opt_global_partitioning), //添加构造函数，主要是为了增加对PT_global_partition的赋值操作
  on_duplicate(on_duplicate),
  opt_query_expression(opt_query_expression),
  opt_like_clause(nullptr) {}
  
//在其对应的函数中增加相关逻辑，调用对应的初始化函数contextualize
Sql_cmd *PT_create_table_stmt::make_cmd(THD *thd) {
    if (opt_global_partitioning){
        if (opt_global_partitioning->contextualize(&pc)) return nullptr;
        lex->part_info = &opt_global_partitioning->part_info;
    }
}