oracle 小数点前零丢失的问题
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