SQL> select to_char(0.003) from dual;

TO_CHAR(
--------
.003

小数转化成字符的时候，前面的0总是没有。
====================================================================================
SQL> select to_char(0.1,'fm9999990.9') from dual;

TO_CHAR(0.1,'FM99999
--------------------
0.1


SQL> select to_char(0.11111,'fm9999990.9') from dual;

TO_CHAR(0.11111,'FM9
--------------------
0.1

恍然大悟，原来to_char也是需要format的。

====================================================================================
SQL> select to_char(123456789.16,'fm9999990.9') from dual;

TO_CHAR(123456789.16
--------------------
##########

SQL> select to_char(1234567.16,'fm9999990.9') from dual;

TO_CHAR(1234567.16,'
--------------------
1234567.2

SQL> select to_char(12345678.16,'fm9999990.9') from dual;

TO_CHAR(12345678.16,
--------------------
##########

to_char的format，小数点前最大是7位，多余7位是#号。

小数点后面的位数和fm小数点的位数相匹配。

====================================================================================
SQL> select to_char(0.16,'fm9999990.9') from dual;

TO_CHAR(0.16,'FM9999
--------------------
0.2

小数点超过format位数的时候，进行四舍五入。

====================================================================================