Question

如果表（由其架构和表定义）具有自动序列属性（AKA标识属性）的列，是否有办法知道使用C ++和ODBC API？

提前致谢

Answer 1

您可以使用TreeMap aTreeMap = new TreeMap(); //call another method to doSonthing woth map doSomeThing(aTreeMap)功能。它提供了一个列表，这些列在事务更新行中的任何值时自动更新。

Answer 2

您可以将SQLColAttribute与字段标识符参数SQL_DESC_AUTO_UNIQUE_VALUE一起使用就像该功能

int fetch_identity(const std::string& sql, int& is_identity)
    {
      SQLHSTMT hstmt;
      is_identity = 0;
      SQLCHAR         colname[32];        // column name
      SQLSMALLINT     coltype;            // column type
      SQLSMALLINT     colnamelen;         // length of column name
      SQLSMALLINT     nullable;           // whether column can have NULL value
      SQLULEN         collen;             // column length
      SQLSMALLINT     decimaldigits;      // no of digits if column is numeric
      SQLLEN          auto_unique_value;;
      SQLINTEGER      idx;
      SQLSMALLINT     nbr_cols;

      if (!SQL_SUCCEEDED(SQLAllocHandle(SQL_HANDLE_STMT, query.m_hdbc, &hstmt)))
      {
      }

      if (!SQL_SUCCEEDED(SQLPrepare(hstmt, (SQLCHAR*)sql.c_str(), SQL_NTS)))
      {
        extract_error(hstmt, SQL_HANDLE_STMT);
      }

      // Get number of nbr_cols from prepared statement
      if (!SQL_SUCCEEDED(SQLNumResultCols(hstmt, &nbr_cols)))
      {
        extract_error(hstmt, SQL_HANDLE_STMT);
      }

      for (idx = 0; idx < nbr_cols; idx++)
      {
        // for each column from the prepared statement in hstmt, get the
        // column name, type, column size, decimal digits, and nullability
        if (!SQL_SUCCEEDED(SQLDescribeCol(hstmt,
          (SQLUSMALLINT)idx + 1,
          colname,
          sizeof(colname),
          &colnamelen,
          &coltype,
          &collen,
          &decimaldigits,
          &nullable)))
        {
          extract_error(hstmt, SQL_HANDLE_STMT);
        }

        auto_unique_value = 0;

        //SQL_DESC_AUTO_UNIQUE_VALUE
        //FieldIdentifier parameter returned in NumericAttributePtr
        //SQL_TRUE if the column is an autoincrementing column.
        //SQL_FALSE if the column is not an autoincrementing column or is not numeric.

        if (!SQL_SUCCEEDED(SQLColAttribute(hstmt,
          (SQLUSMALLINT)idx + 1,
          SQL_DESC_AUTO_UNIQUE_VALUE,
          NULL,
          0,
          NULL,
          &auto_unique_value)))
        {
          extract_error(hstmt, SQL_HANDLE_STMT);
        }
        if (auto_unique_value == 1)
        {
          is_identity = 1;
        }
      }

      SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
      return 0;
    }

此处描述了变量m_hdbc

https://github.com/pedro-vicente/lib_odbc

检查列是否使用ODBC自动递增？

2 个答案: