前端补0的三种方式。
select lpad(sal,8,'0') from emp;
select to_char(sal,'00000000') from emp;
select substr('00000000'||sal,-8) from emp;
关于LPAD函数（转自http://blog.chinaunix.net/u/25102/showart_285842.html）
Oracle/PLSQL: Lpad Function
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In Oracle/PLSQL, the lpad function pads the left-side of a string with a specific set of characters.
The syntax for the lpad function is:
lpad( string1, padded_length, [ pad_string ] )
string1 is the string to pad characters to (the left-hand side).
padded_length is the number of characters to return. If the padded_length is smaller than the original string, the lpad function will truncate the string to the size of padded_length.
pad_string is optional. This is the string that will be padded to the left-hand side of string1. If this parameter is omitted, the lpad function will pad spaces to the left-side of string1.
For example:
lpad('tech', 7); would return ' tech'
lpad('tech', 2); would return 'te'
lpad('tech', 8, '0'); would return '0000tech'
lpad('tech on the net', 15, 'z'); would return 'tech on the net'
lpad('tech on the net', 16, 'z'); would return 'ztech on the net'
lpad('tech', 2); would return 'te'
lpad('tech', 8, '0'); would return '0000tech'
lpad('tech on the net', 15, 'z'); would return 'tech on the net'
lpad('tech on the net', 16, 'z'); would return 'ztech on the net'
Oracle/PLSQL: Lpad Function
--------------------------------------------------------------------------------
In Oracle/PLSQL, the lpad function pads the left-side of a string with a specific set of characters.
The syntax for the lpad function is:
lpad( string1, padded_length, [ pad_string ] )
string1 is the string to pad characters to (the left-hand side).
padded_length is the number of characters to return. If the padded_length is smaller than the original string, the lpad function will truncate the string to the size of padded_length.
pad_string is optional. This is the string that will be padded to the left-hand side of string1. If this parameter is omitted, the lpad function will pad spaces to the left-side of string1.
For example:
lpad('tech', 7); would return ' tech'
lpad('tech', 2); would return 'te'
lpad('tech', 8, '0'); would return '0000tech'
lpad('tech on the net', 15, 'z'); would return 'tech on the net'
lpad('tech on the net', 16, 'z'); would return 'ztech on the net'
lpad('tech', 2); would return 'te'
lpad('tech', 8, '0'); would return '0000tech'
lpad('tech on the net', 15, 'z'); would return 'tech on the net'
lpad('tech on the net', 16, 'z'); would return 'ztech on the net'