查询和修改数据

1.概述

本章节介绍如何使用 ODBC 驱动接入集群并执行各种 SQL 查询。

ODBC 驱动支持 DML（数据修改语言），即用户可以使用 ODBC 连接修改数据。

2.创建表

使用 ODBC 驱动创建表的最简单方法是使用 DDL 语句：

SQLHENV env;

// Allocate an environment handle
SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env);

// Use ODBC ver 3.8
SQLSetEnvAttr(env, SQL_ATTR_ODBC_VERSION, reinterpret_cast<void*>(SQL_OV_ODBC3_80), 0);

SQLHDBC dbc;

// Allocate a connection handle
SQLAllocHandle(SQL_HANDLE_DBC, env, &dbc);

// Prepare the connection string
SQLCHAR connectStr[] = "Driver={Apache Ignite 3};ADDRESS=localhost:10800;SCHEMA=PUBLIC;";

// Connecting to the Cluster.
SQLDriverConnect(dbc, NULL, connectStr, SQL_NTS, NULL, 0, NULL, SQL_DRIVER_COMPLETE);

SQLHSTMT stmt;

// Allocate a statement handle
SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

SQLCHAR query1[] = "CREATE TABLE Person ( "
    "id LONG PRIMARY KEY, "
    "firstName VARCHAR, "
    "lastName VARCHAR, "
    "salary FLOAT)";

SQLExecDirect(stmt, query1, SQL_NTS);

SQLCHAR query2[] = "CREATE TABLE Organization ( "
    "id LONG PRIMARY KEY, "
    "name VARCHAR)";

SQLExecDirect(stmt, query2, SQL_NTS);

SQLCHAR query3[] = "CREATE INDEX idx_organization_name ON Organization (name)";

SQLExecDirect(stmt, query3, SQL_NTS);

3.处理错误

下面会介绍如何使用 ODBC 处理可能出现的错误，在此示例中会处理接入集群的问题：

SQLHENV env;
// Connecting to Ignite Cluster.
SQLRETURN ret = SQLDriverConnect(dbc, NULL, connectStr, SQL_NTS, NULL, 0, NULL, SQL_DRIVER_COMPLETE);

if (!SQL_SUCCEEDED(ret))
{
  SQLCHAR sqlstate[7] = { 0 };
  SQLINTEGER nativeCode;

  SQLCHAR errMsg[BUFFER_SIZE] = { 0 };
  SQLSMALLINT errMsgLen = static_cast<SQLSMALLINT>(sizeof(errMsg));

  SQLGetDiagRec(SQL_HANDLE_DBC, dbc, 1, sqlstate, &nativeCode, errMsg, errMsgLen, &errMsgLen);

  std::cerr << "Failed to connect to Ignite: "
            << reinterpret_cast<char*>(sqlstate) << ": "
            << reinterpret_cast<char*>(errMsg) << ", "
            << "Native error code: " << nativeCode
            << std::endl;

  // Releasing allocated handles.
  SQLFreeHandle(SQL_HANDLE_DBC, dbc);
  SQLFreeHandle(SQL_HANDLE_ENV, env);

  return;
}

4.查询数据

都准备好之后，就可以使用 ODBC API 执行 SELECT：

SQLHSTMT stmt;

// Allocate a statement handle
SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

SQLCHAR query[] = "SELECT firstName, lastName, salary, Organization.name FROM Person "
  "INNER JOIN Organization ON Person.orgId = Organization.id"
SQLSMALLINT queryLen = static_cast<SQLSMALLINT>(sizeof(queryLen));

SQLRETURN ret = SQLExecDirect(stmt, query, queryLen);

if (!SQL_SUCCEEDED(ret))
{
  SQLCHAR sqlstate[7] = { 0 };
  SQLINTEGER nativeCode;

  SQLCHAR errMsg[BUFFER_SIZE] = { 0 };
  SQLSMALLINT errMsgLen = static_cast<SQLSMALLINT>(sizeof(errMsg));

  SQLGetDiagRec(SQL_HANDLE_DBC, dbc, 1, sqlstate, &nativeCode, errMsg, errMsgLen, &errMsgLen);

  std::cerr << "Failed to perform SQL query: "
            << reinterpret_cast<char*>(sqlstate) << ": "
            << reinterpret_cast<char*>(errMsg) << ", "
            << "Native error code: " << nativeCode
            << std::endl;
}
else
{
  // Printing the result set.
  struct OdbcStringBuffer
  {
    SQLCHAR buffer[BUFFER_SIZE];
    SQLLEN resLen;
  };

  // Getting a number of columns in the result set.
  SQLSMALLINT columnsCnt = 0;
  SQLNumResultCols(stmt, &columnsCnt);

  // Allocating buffers for columns.
  std::vector<OdbcStringBuffer> columns(columnsCnt);

  // Binding columns. For simplicity we are going to use only
  // string buffers here.
  for (SQLSMALLINT i = 0; i < columnsCnt; ++i)
    SQLBindCol(stmt, i + 1, SQL_C_CHAR, columns[i].buffer, BUFFER_SIZE, &columns[i].resLen);

  // Fetching and printing data in a loop.
  ret = SQLFetch(stmt);
  while (SQL_SUCCEEDED(ret))
  {
    for (size_t i = 0; i < columns.size(); ++i)
      std::cout << std::setw(16) << std::left << columns[i].buffer << " ";

    std::cout << std::endl;

    ret = SQLFetch(stmt);
  }
}

// Releasing statement handle.
SQLFreeHandle(SQL_HANDLE_STMT, stmt);

列绑定

在上面的示例中，所有列都绑定到SQL_C_CHAR列上，即查询时所有值都将转换为字符串，这只是为了方便演示。查询时的类型转换可能非常慢，因此最好是直接使用实际存储时的数据类型。

5.插入数据

使用SQL的INSERT语句可以插入新的数据：

SQLHSTMT stmt;

// Allocate a statement handle
SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

SQLCHAR query[] =
	"INSERT INTO Person (id, orgId, firstName, lastName, resume, salary) "
	"VALUES (?, ?, ?, ?, ?, ?)";

SQLPrepare(stmt, query, static_cast<SQLSMALLINT>(sizeof(query)));

// Binding columns.
int64_t key = 0;
int64_t orgId = 0;
char name[1024] = { 0 };
SQLLEN nameLen = SQL_NTS;
double salary = 0.0;

SQLBindParameter(stmt, 1, SQL_PARAM_INPUT, SQL_C_SLONG, SQL_BIGINT, 0, 0, &key, 0, 0);
SQLBindParameter(stmt, 2, SQL_PARAM_INPUT, SQL_C_SLONG, SQL_BIGINT, 0, 0, &orgId, 0, 0);
SQLBindParameter(stmt, 3, SQL_PARAM_INPUT, SQL_C_CHAR, SQL_VARCHAR,	sizeof(name), sizeof(name), name, 0, &nameLen);
SQLBindParameter(stmt, 4, SQL_PARAM_INPUT, SQL_C_DOUBLE, SQL_DOUBLE, 0, 0, &salary, 0, 0);

// Filling cache.
key = 1;
orgId = 1;
strncpy(name, "John", sizeof(name));
salary = 2200.0;

SQLExecute(stmt);
SQLMoreResults(stmt);

++key;
orgId = 1;
strncpy(name, "Jane", sizeof(name));
salary = 1300.0;

SQLExecute(stmt);
SQLMoreResults(stmt);

++key;
orgId = 2;
strncpy(name, "Richard", sizeof(name));
salary = 900.0;

SQLExecute(stmt);
SQLMoreResults(stmt);

++key;
orgId = 2;
strncpy(name, "Mary", sizeof(name));
salary = 2400.0;

SQLExecute(stmt);

// Releasing statement handle.
SQLFreeHandle(SQL_HANDLE_STMT, stmt);

下面的示例，将不使用预编译的SQL语句：

SQLHSTMT stmt;

// Allocate a statement handle
SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

SQLCHAR query1[] = "INSERT INTO Organization (id, name) VALUES (1L, 'Some company')";

SQLExecDirect(stmt, query1, static_cast<SQLSMALLINT>(sizeof(query1)));

SQLFreeStmt(stmt, SQL_CLOSE);

SQLCHAR query2[] = "INSERT INTO Organization (id, name) VALUES (2L, 'Some other company')";

  SQLExecDirect(stmt, query2, static_cast<SQLSMALLINT>(sizeof(query2)));

// Releasing statement handle.
SQLFreeHandle(SQL_HANDLE_STMT, stmt);

错误检查

为简单起见，上面的示例代码未检查错误返回代码，在生产中需要进行错误检查。

6.更新数据

下面是使用 UPDATE 语句更新数据的示例：

void AdjustSalary(SQLHDBC dbc, int64_t key, double salary)
{
  SQLHSTMT stmt;

  // Allocate a statement handle
  SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

  SQLCHAR query[] = "UPDATE Person SET salary=? WHERE id=?";

  SQLBindParameter(stmt, 1, SQL_PARAM_INPUT,
      SQL_C_DOUBLE, SQL_DOUBLE, 0, 0, &salary, 0, 0);

  SQLBindParameter(stmt, 2, SQL_PARAM_INPUT, SQL_C_SLONG,
      SQL_BIGINT, 0, 0, &key, 0, 0);

  SQLExecDirect(stmt, query, static_cast<SQLSMALLINT>(sizeof(query)));

  // Releasing statement handle.
  SQLFreeHandle(SQL_HANDLE_STMT, stmt);
}

...
AdjustSalary(dbc, 3, 1200.0);
AdjustSalary(dbc, 1, 2500.0);

7.删除数据

最后，会使用 DELETE 语句删除一些数据：

void DeletePerson(SQLHDBC dbc, int64_t key)
{
  SQLHSTMT stmt;

  // Allocate a statement handle
  SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);

  SQLCHAR query[] = "DELETE FROM Person WHERE id=?";

  SQLBindParameter(stmt, 1, SQL_PARAM_INPUT, SQL_C_SLONG, SQL_BIGINT,
      0, 0, &key, 0, 0);

  SQLExecDirect(stmt, query, static_cast<SQLSMALLINT>(sizeof(query)));

  // Releasing statement handle.
  SQLFreeHandle(SQL_HANDLE_STMT, stmt);
}

...
DeletePerson(dbc, 1);
DeletePerson(dbc, 4);

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