C++ 写法sqlserver 检查数据是否存

可以使用以下代码片段来检查 SQL Server 数据库中是否存在指定数据：

#include <iostream>
#include <windows.h>
#include <sqltypes.h>
#include <sql.h>
#include <sqlext.h>

using namespace std;

int main() {
    SQLHENV henv; // Environment handle
    SQLHDBC hdbc; // Connection handle
    SQLHSTMT hstmt; // Statement handle
    SQLRETURN retcode; // Return code

    // Allocate an environment handle
    retcode = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);

    // Set the ODBC version environment attribute to 3 (ODBC 3.0)
    retcode = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3, SQL_IS_INTEGER);

    // Allocate a connection handle
    retcode = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);

    // Connect to the database
    SQLCHAR* dsn = (SQLCHAR*)"your_dsn_name"; // Data source name
    SQLCHAR* user = (SQLCHAR*)"your_username"; // User name
    SQLCHAR* pass = (SQLCHAR*)"your_password"; // Password
    retcode = SQLConnect(hdbc, dsn, SQL_NTS, user, SQL_NTS, pass, SQL_NTS);

    // Allocate a statement handle
    retcode = SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt);

    // Execute the query to check if data exists
    SQLCHAR* query = (SQLCHAR*)"SELECT COUNT(*) FROM your_table_name WHERE your_condition";
    retcode = SQLExecDirect(hstmt, query, SQL_NTS);

    // Fetch the result
    SQLLEN count;
    retcode = SQLFetch(hstmt);
    if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO) {
        SQLGetData(hstmt, 1, SQL_C_LONG, &count, 0, NULL);
    }

    // Check if the count is greater than zero
    if (count > 0) {
        cout << "Data exists!" << endl;
    } else {
        cout << "Data does not exist!" << endl;
    }

    // Free the statement handle
    retcode = SQLFreeHandle(SQL_HANDLE_STMT, hstmt);

    // Disconnect from the database
    retcode = SQLDisconnect(hdbc);

    // Free the connection handle
    retcode = SQLFreeHandle(SQL_HANDLE_DBC, hdbc);

    // Free the environment handle
    retcode = SQLFreeHandle(SQL_HANDLE_ENV, henv);

    return 0;
}

在以上代码中，你需要将 `your_dsn_name`、`your_username`、`your_password`、`your_table_name` 和 `your_condition` 替换为你的实际值。如果查询到的结果大于零，说明数据存在于数据库中，否则数据不存在。