表中字段追加问题，请高手指导帮助！

CLOSE DATABASES
SELECT * FROM 需追加字段表 INTO CURSOR t1
AFIELDS(aStr)
SELECT * FROM 原表 INTO CURSOR t2 READWRITE && 不喜欢对基础表操作，故用临时表替代
FOR ln = 1 TO ALEN(aStr, 1)
    IF TYPE("t2." + aStr[ln, 1]) == "U"
        ALTER TABLE t2 ADD &aStr[ln, 1] &aStr[ln, 2] (aStr[ln, 3], aStr[ln, 4])
    ENDIF
ENDFOR
MODIFY STRUCTURE