构建一个简单的数据库系列（八）B-tree叶子节点格式之二
英文原文链接：https://cstack.github.io/db_tutorial/parts/part8.html
如何向叶子节点插入数据
这一节我们只实现一个单节点树。回想下上节的内容，一颗树是从一颗空的叶子节点数开始演变的。
图 空树
键值对可以被一直添加直到叶子节点填满。
图 1个节点的B-tree
当第一次打开数据库时，数据库文件是一个空文件，我们初始化page=0，此时它是一个空的叶子节点也是一个空的根节点。
Table* db_open(const char* filename) {
Pager* pager = pager_open(filename);
- uint32_t num_rows = pager->file_length / ROW_SIZE;
Table* table = malloc(sizeof(Table));
table->pager = pager;
- table->num_rows = num_rows;
+ table->root_page_num = 0;
+
+ if (pager->num_pages == 0) {
+ // New database file. Initialize page 0 as leaf node.
+ void* root_node = get_page(pager, 0);
+ initialize_leaf_node(root_node);
+ }
return table;
}
下面我们要定义一个函数，实现向叶子节点插入数据。
/**
* 向叶子节点插入数据
*/
void leaf_node_insert(Cursor *cursor, uint32_t key, Row *value) {
void *node = get_page(cursor->table->pager, cursor->page_num);
uint32_t num_cells = *leaf_node_num_cells(node);
if (num_cells >= LEAF_NODE_MAX_CELLS) {
// Node full
printf("Need to implement splitting a leaf node.\n");
exit(EXIT_FAILURE);
}
if (cursor->cell_num < num_cells) {
// Make room for new cell 会有多个吗？有必要循环吗？TODO
for (uint32_t i = num_cells; i > cursor->cell_num; i--) {
memcpy(leaf_node_cell(node, i), leaf_node_cell(node, i - 1),
LEAF_NODE_CELL_SIZE);
}
}
//写入数据
*(leaf_node_num_cells(node)) += 1;
*(leaf_node_key(node, cursor->cell_num)) = key;
serialize_row(value, leaf_node_value(node, cursor->cell_num));
}我们还没有实现分割，所以node填满后，只能报错。下一步，
当前，我们假设只有1个node，execute_insert函数只是简单地调用这个函数：leaf_node_insert。
ExecuteResult execute_insert(Statement* statement, Table* table) {
- if (table->num_rows >= TABLE_MAX_ROWS) {
+ void* node = get_page(table->pager, table->root_page_num);
+ if ((*leaf_node_num_cells(node) >= LEAF_NODE_MAX_CELLS)) {
return EXECUTE_TABLE_FULL;
}
Row* row_to_insert = &(statement->row_to_insert);
Cursor* cursor = table_end(table);
- serialize_row(row_to_insert, cursor_value(cursor));
- table->num_rows += 1;
+ leaf_node_insert(cursor, row_to_insert->id, row_to_insert);
free(cursor);
通过这些修改，我们的数据库就可以像之前一样正常运行了，除了返回错误：“Table Full”。
打印系统参数命令
+/*打印系统参数*/
+void print_constants() {
+ printf("ROW_SIZE: %d\n", ROW_SIZE);
+ printf("COMMON_NODE_HEADER_SIZE: %d\n", COMMON_NODE_HEADER_SIZE);
+ printf("LEAF_NODE_HEADER_SIZE: %d\n", LEAF_NODE_HEADER_SIZE);
+ printf("LEAF_NODE_CELL_SIZE: %d\n", LEAF_NODE_CELL_SIZE);
+ printf("LEAF_NODE_SPACE_FOR_CELLS: %d\n", LEAF_NODE_SPACE_FOR_CELLS);
+ printf("LEAF_NODE_MAX_CELLS: %d\n", LEAF_NODE_MAX_CELLS);
+}
+
@@ -294,6 +376,14 @@ MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table) {
if (strcmp(input_buffer->buffer, ".exit") == 0) {
db_close(table);
exit(EXIT_SUCCESS);
+ } else if (strcmp(input_buffer->buffer, ".constants") == 0) {
+ printf("Constants:\n");
+ print_constants();
+ return META_COMMAND_SUCCESS;
} else {
return META_COMMAND_UNRECOGNIZED_COMMAND;
}树可视化
为了方便调试和可视化，添加一个元数据命令来打印btree。
+/*打印叶子节点*/
+void print_leaf_node(void* node) {
+ uint32_t num_cells = *leaf_node_num_cells(node);
+ printf("leaf (size %d)\n", num_cells);
+ for (uint32_t i = 0; i < num_cells; i++) {
+ uint32_t key = *leaf_node_key(node, i);
+ printf(" - %d : %d\n", i, key);
+ }
+}
+
@@ -294,6 +376,14 @@ MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table) {
if (strcmp(input_buffer->buffer, ".exit") == 0) {
db_close(table);
exit(EXIT_SUCCESS);
+ } else if (strcmp(input_buffer->buffer, ".btree") == 0) {
+ printf("Tree:\n");
+ print_leaf_node(get_page(table->pager, 0));
+ return META_COMMAND_SUCCESS;
} else if (strcmp(input_buffer->buffer, ".constants") == 0) {
printf("Constants:\n");
print_constants();
return META_COMMAND_SUCCESS;
} else {
return META_COMMAND_UNRECOGNIZED_COMMAND;
}测试执行
db > select
Executed.
db > insert 1 user1 [email protected]
Executed.
db > insert 2 user2 [email protected]
Executed.
db > insert 3 user3 [email protected]
Executed.
db > insert 4 user4 [email protected]
Executed.
db > insert 5 user5 [email protected]
Executed.
db > insert 6 user6 [email protected]
Executed.
db > insert 7 user7 [email protected]
Executed.
db > insert 8 user8 [email protected]
Executed.
db > insert 9 user9 [email protected]
Executed.
db > insert 10 user10 [email protected]
Executed.
db > insert 11 user11 [email protected]
Executed.
db > select
(1, user1, [email protected])
(2, user2, [email protected])
(3, user3, [email protected])
(4, user4, [email protected])
(5, user5, [email protected])
(6, user6, [email protected])
(7, user7, [email protected])
(8, user8, [email protected])
(9, user9, [email protected])
(10, user10, [email protected])
(11, user11, [email protected])
Executed.
db > insert 12 user12 [email protected]
Executed.
db > insert 13 user13 [email protected]
Executed.
db > insert 14 user14 [email protected]
Error: Table full.
db > .btree
Tree:
leaf (size 13)
- 0 : 1
- 1 : 2
- 2 : 3
- 3 : 4
- 4 : 5
- 5 : 6
- 6 : 7
- 7 : 8
- 8 : 9
- 9 : 10
- 10 : 11
- 11 : 12
- 12 : 13
db > .constants
Constants:
ROW_SIZE: 293
COMMON_NODE_HEADER_SIZE: 6
LEAF_NODE_HEADER_SIZE: 10
LEAF_NODE_CELL_SIZE: 297
LEAF_NODE_SPACE_FOR_CELLS: 4086
LEAF_NODE_MAX_CELLS: 13
db >查看数据库文件，正好是4K
至此最新代码：
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* 定义 元数据操作结果*/
enum MetaCommandResult_t {
META_COMMAND_SUCCESS,
META_COMMAND_UNRECOGNIZED_COMMAND
};
typedef enum MetaCommandResult_t MetaCommandResult;
/* 执行结果*/
enum ExecuteResult_t { EXECUTE_SUCCESS, EXECUTE_TABLE_FULL };
typedef enum ExecuteResult_t ExecuteResult;
/* sql解析结果 */
enum PrepareResult_t {
PREPARE_SUCCESS,
PREPARE_NEGATIVE_ID,
PREPARE_STRING_TOO_LONG,
PREPARE_SYNTAX_ERROR,
PREPARE_UNRECOGNIZED_STATEMENT
};
typedef enum PrepareResult_t PrepareResult;
/* 行定义，对应具体的业务 */
const uint32_t COLUMN_USERNAME_SIZE = 32;
const uint32_t COLUMN_EMAIL_SIZE = 255;
struct Row_t {
uint32_t id;
char username[COLUMN_USERNAME_SIZE + 1];
char email[COLUMN_EMAIL_SIZE + 1];
};
typedef struct Row_t Row;
/* sql type*/
enum StatementType_t{
STATEMENT_INSERT,
STATEMENT_SELECT
};
typedef enum StatementType_t StatementType;
struct Statement_t {
StatementType type;
Row row_to_insert; /* only used by insert statement */
};
typedef struct Statement_t Statement;
/**/
#define size_of_attribute(Struct, Attribute) sizeof(((Struct*)0)->Attribute)
const uint32_t ID_SIZE = size_of_attribute(Row, id);
const uint32_t USERNAME_SIZE = size_of_attribute(Row, username);
const uint32_t EMAIL_SIZE = size_of_attribute(Row, email);
const uint32_t ID_OFFSET = 0;
const uint32_t USERNAME_OFFSET = ID_OFFSET + ID_SIZE;
const uint32_t EMAIL_OFFSET = USERNAME_OFFSET + USERNAME_SIZE;
const uint32_t ROW_SIZE = ID_SIZE + USERNAME_SIZE + EMAIL_SIZE;
/* 大部分系统结构的页大小都是4K ，所以这里也定义为4K 这样就不用做转换 */
const uint32_t PAGE_SIZE = 4096;
const uint32_t TABLE_MAX_PAGES = 100;
/*
* 页和表定义
*/
struct Pager_t {
int file_descriptor;
uint32_t file_length;
uint32_t num_pages;
void *pages[TABLE_MAX_PAGES];
};
typedef struct Pager_t Pager;
struct Table_t {
Pager *pager; //Pager管理器
uint32_t root_page_num; //根节点page编号
};
typedef struct Table_t Table;
/**
* Cursor定义
*/
struct Cursor_t {
Table* table;
uint32_t page_num;
uint32_t cell_num;
bool end_of_table; // Indicates a position one past the last element
};
typedef struct Cursor_t Cursor;
enum NodeType_t {
NODE_INTERNAL, NODE_LEAF
};
typedef enum NodeType_t NodeType;
/*
* Common Node Header Layout
*/
const uint32_t NODE_TYPE_SIZE = sizeof(uint8_t);
const uint32_t NODE_TYPE_OFFSET = 0;
const uint32_t IS_ROOT_SIZE = sizeof(uint8_t);
const uint32_t IS_ROOT_OFFSET = NODE_TYPE_SIZE;
const uint32_t PARENT_POINTER_SIZE = sizeof(uint32_t);
const uint32_t PARENT_POINTER_OFFSET = IS_ROOT_OFFSET + IS_ROOT_SIZE;
const uint8_t COMMON_NODE_HEADER_SIZE =
NODE_TYPE_SIZE + IS_ROOT_SIZE + PARENT_POINTER_SIZE;
/*
* Leaf Node Header Layout
*/
const uint32_t LEAF_NODE_NUM_CELLS_SIZE = sizeof(uint32_t);
const uint32_t LEAF_NODE_NUM_CELLS_OFFSET = COMMON_NODE_HEADER_SIZE;
const uint32_t LEAF_NODE_HEADER_SIZE =
COMMON_NODE_HEADER_SIZE + LEAF_NODE_NUM_CELLS_SIZE;
/*
* Leaf Node Body Layout
*/
const uint32_t LEAF_NODE_KEY_SIZE = sizeof(uint32_t);
const uint32_t LEAF_NODE_KEY_OFFSET = 0;
const uint32_t LEAF_NODE_VALUE_SIZE = ROW_SIZE;
const uint32_t LEAF_NODE_VALUE_OFFSET =
LEAF_NODE_KEY_OFFSET + LEAF_NODE_KEY_SIZE;
const uint32_t LEAF_NODE_CELL_SIZE = LEAF_NODE_KEY_SIZE + LEAF_NODE_VALUE_SIZE;
const uint32_t LEAF_NODE_SPACE_FOR_CELLS = PAGE_SIZE - LEAF_NODE_HEADER_SIZE;
const uint32_t LEAF_NODE_MAX_CELLS =
LEAF_NODE_SPACE_FOR_CELLS / LEAF_NODE_CELL_SIZE;
/* 获取cell个数*/
uint32_t *leaf_node_num_cells(void *node) {
return (char *) node + LEAF_NODE_NUM_CELLS_OFFSET;
}
/* 根据cell编码获取相应的cell*/
void *leaf_node_cell(void *node, uint32_t cell_num) {
return (char *) node + LEAF_NODE_HEADER_SIZE + cell_num * LEAF_NODE_CELL_SIZE;
}
/* 根据cell编码获取key*/
uint32_t *leaf_node_key(void *node, uint32_t cell_num) {
return leaf_node_cell(node, cell_num);
}
/* 根据cell编码获取value*/
void *leaf_node_value(void *node, uint32_t cell_num) {
return leaf_node_cell(node, cell_num) + LEAF_NODE_KEY_SIZE;
}
/* 初始化叶子节点 */
void initialize_leaf_node(void *node) { *leaf_node_num_cells(node) = 0; }
/*
* 打印系统参数
*/
void print_constants() {
printf("ROW_SIZE: %d\n", ROW_SIZE);
printf("COMMON_NODE_HEADER_SIZE: %d\n", COMMON_NODE_HEADER_SIZE);
printf("LEAF_NODE_HEADER_SIZE: %d\n", LEAF_NODE_HEADER_SIZE);
printf("LEAF_NODE_CELL_SIZE: %d\n", LEAF_NODE_CELL_SIZE);
printf("LEAF_NODE_SPACE_FOR_CELLS: %d\n", LEAF_NODE_SPACE_FOR_CELLS);
printf("LEAF_NODE_MAX_CELLS: %d\n", LEAF_NODE_MAX_CELLS);
}
/*
* 叶子节点可视化
*/
void print_leaf_node(void *node) {
uint32_t num_cells = *leaf_node_num_cells(node);
printf("leaf (size %d)\n", num_cells);
for (uint32_t i = 0; i < num_cells; i++) {
uint32_t key = *leaf_node_key(node, i);
printf(" - %d : %d\n", i, key);
}
}
/* 序列化： 将row写到内存中 */
void serialize_row(Row* source, void* destination) {
memcpy(destination + ID_OFFSET, &(source->id), ID_SIZE);
memcpy(destination + USERNAME_OFFSET, &(source->username), USERNAME_SIZE);
memcpy(destination + EMAIL_OFFSET, &(source->email), EMAIL_SIZE);
}
/* 反序列化 */
void deserialize_row(void* source, Row* destination) {
memcpy(&(destination->id), source + ID_OFFSET, ID_SIZE);
memcpy(&(destination->username), source + USERNAME_OFFSET, USERNAME_SIZE);
memcpy(&(destination->email), source + EMAIL_OFFSET, EMAIL_SIZE);
}
/**
* 获取页num对应的页
* @param table
* @param row_num
* @return
*/
void *get_page(Pager *pager, uint32_t page_num)
{
if (page_num > TABLE_MAX_PAGES) {
printf("Tried to fetch page number out of bounds. %d > %d\n", page_num,
TABLE_MAX_PAGES);
exit(EXIT_FAILURE);
}
if (pager->pages[page_num] == NULL) {
// Cache miss. Allocate memory and load from file.
void *page = malloc(PAGE_SIZE);
uint32_t num_pages = pager->file_length / PAGE_SIZE;
// We might save a partial page at the end of the file
if (pager->file_length % PAGE_SIZE) {
num_pages += 1;
}
if (page_num <= num_pages) {
lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);
ssize_t bytes_read = read(pager->file_descriptor, page, PAGE_SIZE);
if (bytes_read == -1) {
printf("Error reading file: %d\n", errno);
exit(EXIT_FAILURE);
}
}
pager->pages[page_num] = page;
if (page_num >= pager->num_pages) {
pager->num_pages = page_num + 1;
}
}
return pager->pages[page_num];
}
/**
* 打开pager
* @param filename
* @return
*/
Pager *pager_open(const char *filename)
{
int fd = open(filename,
O_RDWR | // Read/Write mode
O_CREAT, // Create file if it does not exist
S_IWUSR | // User write permission
S_IRUSR // User read permission
);
if (fd == -1) {
printf("Unable to open file\n");
exit(EXIT_FAILURE);
}
off_t file_length = lseek(fd, 0, SEEK_END);
Pager *pager = malloc(sizeof(Pager));
pager->file_descriptor = fd;
pager->file_length = file_length;
pager->num_pages = (file_length / PAGE_SIZE);
if (file_length % PAGE_SIZE != 0) {
printf("Db file is not a whole number of pages. Corrupt file.\n");
exit(EXIT_FAILURE);
}
for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
pager->pages[i] = NULL;
}
return pager;
}
/**
* Cursor api
* @param row
*/
Cursor* table_start(Table* table) {
Cursor* cursor = malloc(sizeof(Cursor));
cursor->table = table;
cursor->page_num = table->root_page_num;
cursor->cell_num = 0;
void* root_node = get_page(table->pager, table->root_page_num);
uint32_t num_cells = *leaf_node_num_cells(root_node);
cursor->end_of_table = (num_cells == 0);
return cursor;
}
Cursor* table_end(Table* table) {
Cursor* cursor = malloc(sizeof(Cursor));
cursor->table = table;
cursor->page_num = table->root_page_num;
void* root_node = get_page(table->pager, table->root_page_num);
uint32_t num_cells = *leaf_node_num_cells(root_node);
cursor->cell_num = num_cells;
cursor->end_of_table = true;
return cursor;
}
/**
* 计算插入位置， 行插入槽
*/
void* cursor_value(Cursor* cursor)
{
uint32_t page_num = cursor->page_num;
void* page = get_page(cursor->table->pager, page_num);
return leaf_node_value(page, cursor->cell_num);
}
/**
* rownum 加1
* @param cursor
*/
void cursor_advance(Cursor* cursor)
{
uint32_t page_num = cursor->page_num;
void* node = get_page(cursor->table->pager, page_num);
cursor->cell_num += 1;
if (cursor->cell_num >= (*leaf_node_num_cells(node))) {
cursor->end_of_table = true;
}
}
void print_row(Row* row) {
printf("(%d, %s, %s)\n", row->id, row->username, row->email);
}
/**
* 打开数据库文件并建立连接
* @param filename
* @return
*/
Table *db_open(const char *filename)
{
Pager *pager = pager_open(filename);
Table *table = malloc(sizeof(Table));
table->pager = pager;
table->root_page_num = 0;
if (pager->num_pages == 0) {
// New database file. Initialize page 0 as leaf node.
void* root_node = get_page(pager, 0);
initialize_leaf_node(root_node);
}
return table;
}
/* 接收输入*/
struct InputBuffer_t {
char* buffer;
size_t buffer_length;
ssize_t input_length;
};
typedef struct InputBuffer_t InputBuffer;
/* 初始化buffer */
InputBuffer* new_input_buffer()
{
InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
input_buffer->buffer = NULL;
input_buffer->buffer_length = 0;
input_buffer->input_length = 0;
return input_buffer;
}
void print_prompt() { printf("db > "); }
/* 按行从标准输入读取 */
void read_input(InputBuffer* input_buffer)
{
ssize_t bytes_read =
getline(&(input_buffer->buffer), &(input_buffer->buffer_length), stdin);
if (bytes_read <= 0) {
printf("Error reading input\n");
exit(EXIT_FAILURE);
}
// Ignore trailing newline
input_buffer->input_length = bytes_read - 1;
input_buffer->buffer[bytes_read - 1] = 0;
}
/**
* 刷新页到文件（指定页号）
* @param pager
* @param page_num
* @param size
*/
void pager_flush(Pager *pager, uint32_t page_num)
{
if (pager->pages[page_num] == NULL) {
printf("Tried to flush null page\n");
exit(EXIT_FAILURE);
}
off_t offset = lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);
if (offset == -1) {
printf("Error seeking: %d\n", errno);
exit(EXIT_FAILURE);
}
ssize_t bytes_written =
write(pager->file_descriptor, pager->pages[page_num], PAGE_SIZE);
if (bytes_written == -1) {
printf("Error writing: %d\n", errno);
exit(EXIT_FAILURE);
}
}
/**
* 关闭数据连接
*/
void db_close(Table *table) {
Pager *pager = table->pager;
for (uint32_t i = 0; i < pager->num_pages; i++) {
if (pager->pages[i] == NULL) {
continue;
}
pager_flush(pager, i);
free(pager->pages[i]);
pager->pages[i] = NULL;
}
int result = close(pager->file_descriptor);
if (result == -1) {
printf("Error closing db file.\n");
exit(EXIT_FAILURE);
}
for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
void *page = pager->pages[i];
if (page) {
free(page);
pager->pages[i] = NULL;
}
}
free(pager);
}
/* 元数据命令处理 */
MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table)
{
if (strcmp(input_buffer->buffer, ".exit") == 0) {
db_close(table);
exit(EXIT_SUCCESS);
} else if (strcmp(input_buffer->buffer, ".btree") == 0) {
printf("Tree:\n");
print_leaf_node(get_page(table->pager, 0));
return META_COMMAND_SUCCESS;
} else if (strcmp(input_buffer->buffer, ".constants") == 0) {
printf("Constants:\n");
print_constants();
return META_COMMAND_SUCCESS;
} else {
return META_COMMAND_UNRECOGNIZED_COMMAND;
}
}
/* insert解析和校验*/
PrepareResult prepare_insert(InputBuffer *input_buffer, Statement *statement) {
statement->type = STATEMENT_INSERT;
char *keyword = strtok(input_buffer->buffer, " ");
char *id_string = strtok(NULL, " ");
char *username = strtok(NULL, " ");
char *email = strtok(NULL, " ");
if (id_string == NULL || username == NULL || email == NULL) {
return PREPARE_SYNTAX_ERROR;
}
int id = atoi(id_string);
if (id < 0) {
return PREPARE_NEGATIVE_ID;
}
if (strlen(username) > COLUMN_USERNAME_SIZE) {
return PREPARE_STRING_TOO_LONG;
}
if (strlen(email) > COLUMN_EMAIL_SIZE) {
return PREPARE_STRING_TOO_LONG;
}
statement->row_to_insert.id = id;
strcpy(statement->row_to_insert.username, username);
strcpy(statement->row_to_insert.email, email);
return PREPARE_SUCCESS;
}
/* sql解析 */
PrepareResult prepare_statement(InputBuffer* input_buffer,Statement* statement)
{
if (strncasecmp(input_buffer->buffer, "insert", 6) == 0) {
return prepare_insert(input_buffer, statement);
}
if (strncasecmp(input_buffer->buffer, "select", 6) == 0) {
statement->type = STATEMENT_SELECT;
return PREPARE_SUCCESS;
}
return PREPARE_UNRECOGNIZED_STATEMENT;
}
/**
* 向叶子节点插入数据
*/
void leaf_node_insert(Cursor *cursor, uint32_t key, Row *value) {
void *node = get_page(cursor->table->pager, cursor->page_num);
uint32_t num_cells = *leaf_node_num_cells(node);
if (num_cells >= LEAF_NODE_MAX_CELLS) {
// Node full
printf("Need to implement splitting a leaf node.\n");
exit(EXIT_FAILURE);
}
if (cursor->cell_num < num_cells) {
// Make room for new cell 会有多个吗？有必要循环吗？TODO
for (uint32_t i = num_cells; i > cursor->cell_num; i--) {
memcpy(leaf_node_cell(node, i), leaf_node_cell(node, i - 1),
LEAF_NODE_CELL_SIZE);
}
}
//写入数据
*(leaf_node_num_cells(node)) += 1;
*(leaf_node_key(node, cursor->cell_num)) = key;
serialize_row(value, leaf_node_value(node, cursor->cell_num));
}
/**
* 执行insert
*/
ExecuteResult execute_insert(Statement *statement, Table *table)
{
void* node = get_page(table->pager, table->root_page_num);
if ((*leaf_node_num_cells(node) >= LEAF_NODE_MAX_CELLS)) {
return EXECUTE_TABLE_FULL;
}
Row *row_to_insert = &(statement->row_to_insert);
Cursor* cursor = table_end(table);
leaf_node_insert(cursor, row_to_insert->id, row_to_insert);
free(cursor);
return EXECUTE_SUCCESS;
}
/* 执行查询*/
ExecuteResult execute_select(Statement *statement, Table *table)
{
Row row;
Cursor* cursor = table_start(table);
while (!(cursor->end_of_table)) {
deserialize_row(cursor_value(cursor), &row);
print_row(&row);
cursor_advance(cursor);
}
free(cursor);
return EXECUTE_SUCCESS;
}
/* sql执行*/
ExecuteResult execute_statement(Statement* statement , Table* table)
{
switch (statement->type)
{
case (STATEMENT_INSERT):
return execute_insert(statement, table);
case (STATEMENT_SELECT):
return execute_select(statement, table);
}
}
/* 主函数*/
int main(int argc, char* argv[])
{
if (argc < 2) {
printf("Must supply a database filename.\n");
exit(EXIT_FAILURE);
}
char *filename = argv[1];
Table *table = db_open(filename);
InputBuffer *input_buffer = new_input_buffer();
while (true)
{
print_prompt();
read_input(input_buffer);
if (input_buffer->buffer[0] == '.')
{
switch (do_meta_command(input_buffer,table))
{
case (META_COMMAND_SUCCESS):
continue;
case (META_COMMAND_UNRECOGNIZED_COMMAND):
printf("Unrecognized command '%s'\n", input_buffer->buffer);
continue;
}
}
Statement statement;
switch (prepare_statement(input_buffer, &statement))
{
case (PREPARE_SUCCESS):
break;
case (PREPARE_NEGATIVE_ID):
printf("ID must be positive.\n");
continue;
case (PREPARE_STRING_TOO_LONG):
printf("String is too long.\n");
continue;
case (PREPARE_SYNTAX_ERROR):
printf("Syntax error. Could not parse statement.\n");
continue;
case (PREPARE_UNRECOGNIZED_STATEMENT):
printf("Unrecognized keyword at start of '%s'.\n",
input_buffer->buffer);
continue;
}
switch (execute_statement(&statement, table))
{
case (EXECUTE_SUCCESS):
printf("Executed.\n");
break;
case (EXECUTE_TABLE_FULL):
printf("Error: Table full.\n");
break;
}
}
}