MySQL Source parser

The SQL request is sent to the server side, and the internal data structure object needs to be generated by the parser to facilitate optimization and generation of execution plans. Parser mainly do two things, lexical analysis and grammar analysis. lexical and syntactic analysis: MySQL uses the lex lexical analyzer, YACC parser for parsing, and finally saves it in the Lex object structure. For example: Select ID, name from xpchild where Id=11. Use Lex_start to initialize the Thd->lex object in the Mysql_parse function, and then invoke the Mysqlparse function in YACC for lexical and syntactic analysis. sql_yacc.cc is a source file generated by YACC after compiling, and a large number of syntax rules are defined in the Sql_yacc.yy file. The syntax definition for select is found below.2. Syntax parsing section:　　Based on the parsing results of the lexical analyzer, the following syntax rules are applied　　

%token Select_symSelect: select_init {LEX*lex=Lex; Lex->sql_command=Sqlcom_select;     }; Select_item_list:select_item_list','Select_item|Select_item|'*'{THD*thd=YYTHD; Item*item=New(Thd->mem_root) Item_field (&thd->lex->current_select->context,null, NULL,"*"); if(Item = =NULL)            Mysql_yyabort; if(Add_item_to_list (THD, item)) Mysql_yyabort; (THD->lex->current_select->with_wild) + +; };where_clause:/*Empty*/{select->where=0; } |WHERE {Select->parsing_place=In_where; } expr {Select_lex*Select=Select; Select-where= $3; Select->parsing_place=No_matter; if($3)              $3-Top_level_item (); };

You can see that the above SQL statement is parsed out of several parts: (saved in the lex structure) 1.     Sql_command=sqlcom_select; 2. WHERE clause: Select_lex->where 3. Table list: Select_lex->table_list 4.　　Field List: Select_lex->item_list specific content: 1. Table_list

     (gdb) Print select_lex->table_list       $= {            <Sql_alloc> = {<no data Fields>},                 members of Sql_i_list <TABLE_LIST>:                 1,                  0x8ca04818 ,                  0x8ca04818

only one table, db = 0x8ca04bc8 "Test", table_name = 0x8ca047f0 "Xpchild"　2. Where

          (gdb) Print select_lex->where-type ()                    $=  item::func_item          (GDB) p Select_lex,where)->args),type ()                    $=  item::field_item          (GDB) p Select_lex,where)->args++),type ()                    $= Item :: Int_item

The structure is as follows:

where     | --         func_item|-->field_item ("ID")         |-->int_item ( 1)

3. Item_list

          (GDB) print * (item_field*) (select_lex->item_list->first->info)                         0x8ca04758"  ID",          * (item_field*) (select_lex->item_list->first->next->  info)                          0x8cb047f8"name"

The structure is as follows:

item_list:     | -->item_field ("ID")     |-->item_field ("name") )