前段时间做了一个简单的内存数据库，需要提供点简单的SQL支持，在参考了《Lex与Yacc》和网上的相关资料后，以《Lex与Yacc》中的SQL解释器为基础，做了修改，最后生成了一个简单的SQL解释器。
这个SQL解释器由于本身内存数据库提供的功能限制，提供的SQL也有很多的限制：
1、select不支持按字段取值，一次查询获取所有字段
2、查询条件之间的关系只支持AND
3、UPDATE一次只更新一个字段
4、不支持函数
在SQL解释器中，关键是我们要构建我们的语法结构，也就是最终通过SQL解释器要生成的一个程序能识别的结构。负责的SQL支持对应负责的负责的结构，因为我们支持的SQL简单，所以相对应的结构也就很简单了。
主题程序由3个文件组成，sql_plan.h parser_lex.l parser_yacc.y。其中，sql_plan.h是语法结构的定义，parser_lex.l是词法解释和主程序入口部分，parser_yacc.y是语法解释部分。
#ifndef __SQL_DEFINE__
#define __SQL_DEFINE__
#define NAME_SIZE 24
#define MAX_BUFFER_SIZE 8192
typedef enum
{
SQL_SELECT = 1,
SQL_INSERT,
SQL_UPDATE,
SQL_DELETE,
SQL_COUNT_ALL
}sql_action;
typedef struct{
char field_name[NAME_SIZE];
char field_value[256];
}FieldNameValue;
typedef struct{
int list_len;
FieldNameValue fnv_par[5];
}FieldNameValue_List;
typedef struct{
int action;
char tab_name[256];
FieldNameValue_List w_fnv_list;
char u_field_name[256];
char u_field_value[256];
int pos;
char buffer[MAX_BUFFER_SIZE];
}SQL_PLAN;
extern SQL_PLAN sql_plan;
#endif
sql_plan.h
parser_lex.l%{
#include "parser_yacc.h"
#include "sql_define.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int lineno = 1;
void yyerror(char *s);
void TrimString(char *str)
{
char *copied, *tail = NULL;
if ( str == NULL )
return;
for( copied = str; *str; str++ )
{
if ( *str != ' ' && *str != '\t' && *str != '\n' &&
*str != '\r' && *str != '\'' && *str != ';')
{
*copied++ = *str;
tail = copied;
}
else
{
if ( tail )
*copied++ = *str;
}
}
if ( tail )
*tail = 0;
else
*copied = 0;
return;
}
char *_xInput;
int _xLen = 0;
int myinput(char *buff,int max)
{
if(!_xLen) return 0;
if(max > _xLen) max = _xLen ;
memcpy(buff,_xInput,max);
_xInput += max;
_xLen -= max;
return max;
}
#define YY_INPUT(b, r, m) (r = myinput(b, m))
%}
%%
and { return AND; }
CHAR(ACTER)? { return CHARACTER; }
CLOSE { return CLOSE; }
CREATE { return CREATE; }
CURRENT { return CURRENT; }
CURSOR { return CURSOR; }
count { return COUNT; }
DECLARE { return DECLARE; }
delete { return DELETE; }
DOUBLE { return DOUBLE; }
FETCH { return FETCH; }
FLOAT { return FLOAT; }
FOR { return FOR; }
from { return FROM; }
insert { return INSERT; }
INT(EGER)? { return INTEGER; }
into { return INTO; }
NOT { return NOT; }
NULL { return NULLX; }
NUMERIC { return NUMERIC; }
OF { return OF; }
OPEN { return OPEN; }
OR { return OR; }
REAL { return REAL; }
select { return SELECT; }
set { return SET; }
table { return TABLE; }
update { return UPDATE; }
values { return VALUES; }
where { return WHERE; }
/* punctuation */
"=" { return L_EQ; }
"<>" |
"<" |
">" |
"<=" |
">=" { return COMPARISON; }
[-+*/:(),.;] { return yytext[0]; }
/* names */
[A-Za-z][A-Za-z0-9_]* { strcpy(yylval.nameval,yytext); return NAME; }
/* numbers */
-?[0-9]+ { yylval.intval = atoi(yytext); return INTNUM; }
[0-9]+"."[0-9]* { yylval.floatval = atof(yytext); return FLOATNUM; }
[0-9]+[eE][+-]?[0-9]+ |
[0-9]+"."[0-9]*[eE][+-]?[0-9]+ |
"."[0-9]*[eE][+-]?[0-9]+ { return APPROXNUM; }
/* strings */
'[^'\n]*' { TrimString(yytext); strcpy(yylval.strval,yytext); return STRING; }
'[^\'\n]*$ { yyerror("Unterminated string"); }
\n lineno++;
[ \t\r]+ ; /* white space */
"--".*$ ; /* comment */
%%
void yyerror(char *s)
{
printf("%d: %s at %s\n", lineno, s, yytext);
}
int yywrap() {return 1;}
main(int argc, char **argv)
{
int pos;
int ret;
char *buffer;
char prompt_buffer[MAX_BUFFER_SIZE];
char last_prompt_buffer[MAX_BUFFER_SIZE];
int count;
while(1)
{
printf("mdbsql>>");
fgets(prompt_buffer, sizeof(prompt_buffer), stdin);
_xInput = prompt_buffer;
_xLen = strlen(prompt_buffer);
if (prompt_buffer[0]=='\\')
{
strcpy(prompt_buffer, last_prompt_buffer);
_xLen = strlen(prompt_buffer);
}
if (strncmp(prompt_buffer, "quit", 4)==0 ||
strncmp(prompt_buffer, "exit", 4)==0
)
{
break;
}
memset(&sql_plan, 0, sizeof(sql_plan) );
strcpy(last_prompt_buffer, prompt_buffer);
if(!yyparse())
{
if (sql_plan.action == SQL_SELECT)
{
printf("%d records are retrieved\n", count);
}
else if (sql_plan.action == SQL_DELETE)
{
printf("%d records are deleted\n", ret);
}
else if (sql_plan.action == SQL_UPDATE)
{
printf("%d records are updated\n", ret);
}
else if (sql_plan.action == SQL_INSERT)
{
if (ret>0) printf("1 record is inserted\n");
}
else if (sql_plan.action == SQL_COUNT_ALL)
{
if (ret>0) printf("1 record is retrieved\n");
}
}
else
{
printf("SQL parse failed\n");
}
}
}
parser_yacc.y%{
#include "parser_yacc.h"
#include "sql_define.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int lineno = 1;
void yyerror(char *s);
void TrimString(char *str)
{
char *copied, *tail = NULL;
if ( str == NULL )
return;
for( copied = str; *str; str++ )
{
if ( *str != ' ' && *str != '\t' && *str != '\n' &&
*str != '\r' && *str != '\'' && *str != ';')
{
*copied++ = *str;
tail = copied;
}
else
{
if ( tail )
*copied++ = *str;
}
}
if ( tail )
*tail = 0;
else
*copied = 0;
return;
}
char *_xInput;
int _xLen = 0;
int myinput(char *buff,int max)
{
if(!_xLen) return 0;
if(max > _xLen) max = _xLen ;
memcpy(buff,_xInput,max);
_xInput += max;
_xLen -= max;
return max;
}
#define YY_INPUT(b, r, m) (r = myinput(b, m))
%}
%%
and { return AND; }
CHAR(ACTER)? { return CHARACTER; }
CLOSE { return CLOSE; }
CREATE { return CREATE; }
CURRENT { return CURRENT; }
CURSOR { return CURSOR; }
count { return COUNT; }
DECLARE { return DECLARE; }
delete { return DELETE; }
DOUBLE { return DOUBLE; }
FETCH { return FETCH; }
FLOAT { return FLOAT; }
FOR { return FOR; }
from { return FROM; }
insert { return INSERT; }
INT(EGER)? { return INTEGER; }
into { return INTO; }
NOT { return NOT; }
NULL { return NULLX; }
NUMERIC { return NUMERIC; }
OF { return OF; }
OPEN { return OPEN; }
OR { return OR; }
REAL { return REAL; }
select { return SELECT; }
set { return SET; }
table { return TABLE; }
update { return UPDATE; }
values { return VALUES; }
where { return WHERE; }
/* punctuation */
"=" { return L_EQ; }
"<>" |
"<" |
">" |
"<=" |
">=" { return COMPARISON; }
[-+*/:(),.;] { return yytext[0]; }
/* names */
[A-Za-z][A-Za-z0-9_]* { strcpy(yylval.nameval,yytext); return NAME; }
/* numbers */
-?[0-9]+ { yylval.intval = atoi(yytext); return INTNUM; }
[0-9]+"."[0-9]* { yylval.floatval = atof(yytext); return FLOATNUM; }
[0-9]+[eE][+-]?[0-9]+ |
[0-9]+"."[0-9]*[eE][+-]?[0-9]+ |
"."[0-9]*[eE][+-]?[0-9]+ { return APPROXNUM; }
/* strings */
'[^'\n]*' { TrimString(yytext); strcpy(yylval.strval,yytext); return STRING; }
'[^\'\n]*$ { yyerror("Unterminated string"); }
\n lineno++;
[ \t\r]+ ; /* white space */
"--".*$ ; /* comment */
%%
void yyerror(char *s)
{
printf("%d: %s at %s\n", lineno, s, yytext);
}
int yywrap() {return 1;}
main(int argc, char **argv)
{
int pos;
int ret;
char *buffer;
char prompt_buffer[MAX_BUFFER_SIZE];
char last_prompt_buffer[MAX_BUFFER_SIZE];
int count;
while(1)
{
printf("mdbsql>>");
fgets(prompt_buffer, sizeof(prompt_buffer), stdin);
_xInput = prompt_buffer;
_xLen = strlen(prompt_buffer);
if (prompt_buffer[0]=='\\')
{
strcpy(prompt_buffer, last_prompt_buffer);
_xLen = strlen(prompt_buffer);
}
if (strncmp(prompt_buffer, "quit", 4)==0 ||
strncmp(prompt_buffer, "exit", 4)==0
)
{
break;
}
memset(&sql_plan, 0, sizeof(sql_plan) );
strcpy(last_prompt_buffer, prompt_buffer);
if(!yyparse())
{
if (sql_plan.action == SQL_SELECT)
{
printf("%d records are retrieved\n", count);
}
else if (sql_plan.action == SQL_DELETE)
{
printf("%d records are deleted\n", ret);
}
else if (sql_plan.action == SQL_UPDATE)
{
printf("%d records are updated\n", ret);
}
else if (sql_plan.action == SQL_INSERT)
{
if (ret>0) printf("1 record is inserted\n");
}
else if (sql_plan.action == SQL_COUNT_ALL)
{
if (ret>0) printf("1 record is retrieved\n");
}
}
else
{
printf("SQL parse failed\n");
}
}
}
mdbsql: parser_yacc.o parser_lex.o
gcc -o $@ parser_yacc.o parser_lex.o -lfl
parser_yacc.c parser_yacc.h: parser_yacc.y
yacc -vdt parser_yacc.y
mv y.tab.h parser_yacc.h
mv y.tab.c parser_yacc.c
mv y.output parser_yacc.out
parser_lex.o: parser_yacc.h parser_lex.c
parser_lex.c : parser_lex.l
flex $<
mv lex.yy.c $*.c
Makefile
上述程序在cygwin、redhat as5下测试过
