SUBSTR

Syntax

substr::=

Description of the illustration substr.eps

Purpose

The SUBSTR functions return a portion of char, beginning at character position, substring_length characters long. SUBSTR calculates lengths using characters as defined by the input character set. SUBSTRB uses bytes instead of characters. SUBSTRC uses Unicode complete characters. SUBSTR2 uses UCS2 code points. SUBSTR4 uses UCS4 code points.

• If position is 0, then it is treated as 1.

• If position is positive, then Oracle Database counts from the beginning of char to find the first character.

• If position is negative, then Oracle counts backward from the end of char.

• If substring_length is omitted, then Oracle returns all characters to the end of char. If substring_length is less than 1, then Oracle returns null.

char can be any of the data types CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. The exceptions are SUBSTRC, SUBSTR2, and SUBSTR4, which do not allow char to be a CLOB or NCLOB. Both position and substring_length must be of data type NUMBER, or any data type that can be implicitly converted to NUMBER, and must resolve to an integer. The return value is the same data type as char, except that for a CHAR argument a VARCHAR2 value is returned, and for an NCHAR argument an NVARCHAR2 value is returned. Floating-point numbers passed as arguments to SUBSTR are automatically converted to integers.

See Also:

• For a complete description of character length see Oracle Database Globalization Support Guide and Oracle Database SecureFiles and Large Objects Developer's Guide

• Oracle Database Globalization Support Guide for more information about SUBSTR functions and length semantics in different locales

• Appendix C in Oracle Database Globalization Support Guide for the collation derivation rules, which define the collation assigned to the character return value of SUBSTR

Examples

The following example returns several specified substrings of "ABCDEFG":

SELECT SUBSTR('ABCDEFG',3,4) "Substring"
     FROM DUAL;
 
Substring
---------
CDEF

SELECT SUBSTR('ABCDEFG',-5,4) "Substring"
     FROM DUAL;

Substring
---------
CDEF

Assume a double-byte database character set:

SELECT SUBSTRB('ABCDEFG',5,4.2) "Substring with bytes"
     FROM DUAL;

Substring with bytes
--------------------
CD