to_char(1210.73, \'9999.9\') would return \'1210.7\'

　　to_char(1210.73, \'9,999.99\') would return \'1,210.73\'

　　to_char(1210.73, \'$9,999.00\') would return \'$1,210.73\'

　　to_char(21, \'000099\') would return \'000021\'

　　The following is a list of valid parameters when the to_char function is used to convert a date to a string. These parameters can be used in many combinations.

　　Parameter Explanation

　　YEAR Year, spelled out

　　YYYY 4-digit year

　　YYY

　　YY

　　Y Last 3, 2, or 1 digit(s) of year.

　　IYY

　　IY

　　I Last 3, 2, or 1 digit(s) of ISO year.

　　IYYY 4-digit year based on the ISO standard

　　Q Quarter of year (1, 2, 3, 4; JAN-MAR = 1).

　　MM Month (01-12; JAN = 01).

　　MON Abbreviated name of month.

　　MONTH Name of month, padded with blanks to length of 9 characters.

　　RM Roman numeral month (I-XII; JAN = I).

　　WW Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.

　　W Week of month (1-5) where week 1 starts on the first day of the month and ends on the seventh.

　　IW Week of year (1-52 or 1-53) based on the ISO standard.

　　D Day of week (1-7).

　　DAY Name of day.

　　DD Day of month (1-31).

　　DDD Day of year (1-366).

　　DY Abbreviated name of day.

　　J Julian day; the number of days since January 1, 4712 BC.

　　HH Hour of day (1-12).

　　HH12 Hour of day (1-12).

　　HH24 Hour of day (0-23).

　　MI Minute (0-59).

　　SS Second (0-59).

　　SSSSS Seconds past midnight (0-86399).

　　FF Fractional seconds.

　　The following are date examples for the to_char function.

　　to_char(sysdate, \'yyyy/mm/dd\'); would return \'2003/07/09\'

　　to_char(sysdate, \'Month DD, YYYY\'); would return \'July 09, 2003\'

　　to_char(sysdate, \'FMMonth DD, YYYY\'); would return \'July 9, 2003\'

　　to_char(sysdate, \'MON DDth, YYYY\'); would return \'JUL 09TH, 2003\'

　　to_char(sysdate, \'FMMON DDth, YYYY\'); would return \'JUL 9TH, 2003\'

　　to_char(sysdate, \'FMMon ddth, YYYY\'); would return \'Jul 9th, 2003\'

　　You will notice that in some examples, the format_mask parameter begins with \"FM\". This means that zeros and blanks are suppressed. This can be seen in the examples below.

　　to_char(sysdate, \'FMMonth DD, YYYY\'); would return \'July 9, 2003\'

　　to_char(sysdate, \'FMMON DDth, YYYY\'); would return \'JUL 9TH, 2003\'

　　to_char(sysdate, \'FMMon ddth, YYYY\'); would return \'Jul 9th, 2003\'

　　The zeros have been suppressed so that the day component shows as \"9\" as opposed to \"09\".

　　Oracle函数to_char转化数字型指定小数点位数的用法

　　to_char，函数功能，就是将数值型或者日期型转化为字符型。

　　比如最简单的应用：

　　/*1.0123--->\'1.0123\'*/

　　Select TO_CHAR(1.0123) FROM DUAL

　　/*123--->\'123\'*/

　　Select TO_CHAR(123) FROM DUAL

　　接下来再看看下面：

　　/*0.123 ---> \'.123\' */

　　SELEC TO_CHAR(0.123) FROM DUAL

　　上面的结果 \'.123\' 在大多数情况下都不是我们想要的结果，我们想要的应该是 \'0.123\'。

　　我们来看一下to_char函数的具体用法：

　　TO_CHAR ( n [, fmt [, \'nlsparam\']] )

　　该函数将NUMBER类型的n按数值格式fmt转换成VARCHAR2类型的值。\'nlsparams\'指定由数值格式的元素返回的字符,包括:

　　．小数点字符

　　．组分隔符

　　．本地钱币符号

　　．国际钱币符号

　　变元的形式为：

　　\'NLS_NUMERIC_CHARACTERS=\"dg\" NLS_CURRENCY=\"tcxt\" NLS_ISO_CURRENCY=territory\'

　　其中d为小数点字符,g为组分隔符。

　　例 :TO_CHAR (17145,\'L099G999\',\'NLS_NUMERIC_CHARACTERS=\".,\" NLS_CURRENCY=\"NUD\"\')=NUD017,145

　　通过上面的了解，再查看fmt的一些格式，我们可以用以下表达式得到\'0.123\'的值：

　　/*0.123 ---> \' 0.123\' */

　　Select TO_CHAR(0.123,\'0.999\') FROM DUAL

　　/*100.12 ---> \'######\' */

　　Select TO_CHAR(100.12,\'0.999\') F