oracle查询不显示小数点前的0

1.问题起源 
      oracle 数据库字段值为小于1的小数时，使用char类型处理，会丢失小数点前面的0 
      例如0.35就变成了.35 
2.解决办法:用to_char函数格式化数字显示 
      select     to_char(0.338,'fm9999999990.00') from dual; 
     结果:0.34 
     这里重点要看 fm9999999999.99,表示整数部分最多10位,小数部分2位,fm表示去 掉转位字符串后前面的空格,不加fm,0.34前面会有空格的.

3.with的使用 
WITH TMP1 AS ( 
     SELECT 1 AS A, 2 AS B FROM DUAL 
     UNION 
     SELECT 1 AS A, 3 AS B FROM DUAL 
     UNION 
     SELECT 1 AS A, 4 AS B FROM DUAL 
), 
TMP2 AS ( 
     SELECT 1 AS A, 2 AS B FROM DUAL 
     UNION 
     SELECT 1 AS A, 3 AS B FROM DUAL 
     UNION 
     SELECT 2 AS A, 4 AS B FROM DUAL 
) 
SELECT TMP1.*,TMP2.* 
FROM TMP1 JOIN TMP2 
ON TMP1.A = TMP2.A

作者“努力向前”

经过测试，怀疑是number转为char时，舍去了小数点前面的0

1. SQL> select to_char(num,'999999999.999999999') from ml_test;
2. TO_CHAR(NUM,'999999999.9999999
3. ------------------------------
4. .421240000
5. .421246543
6. 65432.421243240
7. 4.621240000
8. SQL> select to_char(num) from ml_test;
9. TO_CHAR(NUM)
10. ----------------------------------------
11. .42124
12. .4212465434
13. 65432.42124324
14. 4.62124
15. SQL> select to_char(0.99) from dual;
16. TO_CHAR(0.99)
17. -------------
18. .99

--4.怎么解决，解决方案如下

（1）

1. SQL>  select to_nmber(to_char(0.99)) from dual;
2. TO_NUMBER(TO_CHAR(0.99))
3. ------------------------
4. 0.99
5. SQL>  select to_char(num,'fm999999990.999999999') from ml_test;
6. TO_CHAR(NUM,'FM999999990.99999
7. ------------------------------
8. 0.42124
9. 0.421246543
10. 65432.42124324
11. 4.62124

（2）使用case when 或 decode函数，取第一位是否为".", 补0 ，就ok了

1. SQL> select to_char(num,'999999999.999999999') from ml_test;
2. TO_CHAR(NUM,'999999999.9999999
3. ------------------------------
4. .421240000
5. .421246543
6. 65432.421243240
7. 4.621240000
8. SQL> select to_char(num) from ml_test;
9. TO_CHAR(NUM)
10. ----------------------------------------
11. .42124
12. .4212465434
13. 65432.42124324
14. 4.62124
15. SQL> select to_char(0.99) from dual;
16. TO_CHAR(0.99)
17. -------------
18. .99