number----char(to_char)

1,number----char(to_char) 一个数字在转成字符类型，在指定了格式时正数会多一个字节用来存储前面的‘+’ SQL> select length(23),length(-23) from dual; LENGTH(23) LENGTH(-23) ---------- -----------          2           3 SQL> select length(to_char(23)),length(to_char(-23)) from dual; LENGTH(TO_CHAR(23)) LENGTH(TO_CHAR(-23)) ------------------- --------------------                   2                    3 SQL> select length(to_char(23,'99')),length(to_char(-23,'99')) from dual; LENGTH(TO_CHAR(23,'99')) LENGTH(TO_CHAR(-23,'99')) ------------------------ -------------------------                        3                         3 多出的占位符用空格补充 SQL> select length(to_char(23,'S99')),length(to_char(0,'S99')) from dual; LENGTH(TO_CHAR(23,'STM9')) LENGTH(TO_CHAR(0,'S99')) -------------------------- ------------------------                          3                        3                          可以通过使用‘S’来显示‘+’ SQL> select to_char(23,'S99'),to_char(-23,'S99') from dual; TO_CHAR(23,'S99') TO_CHAR(-23,'S99') ----------------- ------------------ SQL> select length(to_char(23,'TM9')),length(to_char(-23,'TM9')) from dual; LENGTH(TO_CHAR(23,'TM9')) LENGTH(TO_CHAR(-23,'TM9')) ------------------------- --------------------------                         2                          3                          TM最小格式输出，会去掉空格以及前面的‘+’，同不带格式参数一样 SQL> select length(to_char(23,'TM9')),length(to_char(-23,'TM9')) from dual; LENGTH(TO_CHAR(23,'TM9')) LENGTH(TO_CHAR(-23,'TM9')) ------------------------- --------------------------                         2                          3