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Http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions181.htm#i87066

Substr syntax:

The substr function returns the part of the character, starting with postition, and returns the optional character length substring_length. Substr calculates the length based on the number of bytes in the char character set. Substrb is calculated using digits bytes, substrc through unicode,substr2 through UCS2 code, substr4 through UCS4

If postition is positioned at 0, the effect is the same as 1.

If postition is positioned as a positive number, the Oracle database starts with the first letter of the char character set

If postition is positioned as a negative number, the Oracle database starts with the last letter of the char character set

If substring_length is omitted, Oracle returns all characters positioned from position to the end of the character set. If substring_length

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