var
  Fld: TIBXSQLVAR;
begin
  IBSQL1.SQL.Text := 'SELECT t.id as new_id FROM mytable t';
  IBSQL1.Prepare;
  Fld := IBSQL1.Fields[0];
end;

    property XSqlVar : Pointer read GetSQLVAR write SetSQLVAR;
    property SqlType : Short read GetSqlType write SetSqlType;
    property SqlDef : Short read GetSqlDef;
    property SqlScale : Short read GetSqlScale write SetSqlScale;
    property SqlPrecision : Short read GetSqlPrecision write SetSqlPrecision;
    property SqlSubtype : Short read GetSqlSubtype write SetSqlSubtype;
    property SqlLen : Short read GetSqlLen write SetSqlLen;
    property SqlData : PByte read GetSqlData write SetSqlData;
    property SqlInd : PShort read GetSqlInd write SetSqlInd;

    property SqlName : String read GetSqlName write SetSqlName;
    property RelName : String read GetRelName write SetRelName;
    property OwnName : String read GetOwnName write SetOwnName;
    property AliasName : String read GetAliasName write SetAliasName;

  TXSQLVAR_V1 = record
    sqltype                     : Short;     (** datatype of field **)
    sqlscale                    : Short;     (** scale factor **)
    sqlsubtype                  : Short;     (** datatype subtype - BLOBs **)
					                                   (** & text types only **)
    sqllen                      : Short;     (** length of data area **)
    sqldata                     : PByte;     (** address of data **)
    sqlind                      : PShort;    (** address of indicator **)
                                             (** variable **)
    sqlname_length              : Short;     (** length of sqlname field **)
    (** name of field, name length + space for NULL **)
    sqlname                     : array[0..31] of Byte;
    relname_length              : Short;     (** length of relation name **)
    (** field's relation name + space for NULL **)
    relname                     : array[0..31] of Byte;
    ownname_length              : Short;     (** length of owner name **)
    (** relation's owner name + space for NULL **)
    ownname                     : array[0..31] of Byte;
    aliasname_length            : Short;     (** length of alias name **)
    (** relation's alias name + space for NULL **)
    aliasname                   : array[0..31] of Byte;
  end;  // TXSQLVAR_V1

typedef struct
{
        ISC_SHORT       sqltype;                        
        ISC_SHORT       sqlscale;                       
        ISC_SHORT       sqlsubtype;                     
        ISC_SHORT       sqllen;                         
        ISC_SCHAR*      sqldata;                        
        ISC_SHORT*      sqlind;                         
        ISC_SHORT       sqlname_length;         
        ISC_SCHAR       sqlname[32];            
        ISC_SHORT       relname_length;         
        ISC_SCHAR       relname[32];            
        ISC_SHORT       ownname_length;         
        ISC_SCHAR       ownname[32];            
        ISC_SHORT       aliasname_length;       
        ISC_SCHAR       aliasname[32];          
} XSQLVAR;