INSTR

Syntax

Description of the illustration instr.eps

Purpose

The INSTR functions search string for substring. The search operation is defined as comparing the substring argument with substrings of string of the same length for equality until a match is found or there are no more substrings left. Each consecutive compared substring of string begins one character to the right (for forward searches) or one character to the left (for backward searches) from the first character of the previous compared substring. If a substring that is equal to substring is found, then the function returns an integer indicating the position of the first character of this substring. If no such substring is found, then the function returns zero.

position is an nonzero integer indicating the character of string where Oracle Database begins the search—that is, the position of the first character of the first substring to compare with substring. If position is negative, then Oracle counts backward from the end of string and then searches backward from the resulting position.
occurrence is an integer indicating which occurrence of substring in string Oracle should search for. The value of occurrence must be positive. If occurrence is greater than 1, then the database does not return on the first match but continues comparing consecutive substrings of string, as described above, until match number occurrence has been found.

INSTR accepts and returns positions in characters as defined by the input character set, with the first character of string having position 1. INSTRB uses bytes instead of characters. INSTRC uses Unicode complete characters. INSTR2 uses UCS2 code points. INSTR4 uses UCS4 code points.

string can be any of the data types CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. The exceptions are INSTRC, INSTR2, and INSTR4, which do not allow string to be a CLOB or NCLOB.

substring can be any of the data types CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB.

The value returned is of NUMBER data type.

Both position and occurrence must be of data type NUMBER, or any data type that can be implicitly converted to NUMBER, and must resolve to an integer. The default values of both position and occurrence are 1, meaning Oracle begins searching at the first character of string for the first occurrence of substring. The return value is relative to the beginning of string, regardless of the value of position.

See Also:

Table 2-8 for more information on implicit conversion
Appendix C in Oracle Database Globalization Support Guide for the collation determination rules, which define the collation the INSTR functions use to compare the substring argument with substrings of string

Examples

The following example searches the string CORPORATE FLOOR, beginning with the third character, for the string "OR". It returns the position in CORPORATE FLOOR at which the second occurrence of "OR" begins:

SELECT INSTR('CORPORATE FLOOR','OR', 3, 2) "Instring"
  FROM DUAL;
 
  Instring
----------
        14

In the next example, Oracle counts backward from the last character to the third character from the end, which is the first O in FLOOR. Oracle then searches backward for the second occurrence of OR, and finds that this second occurrence begins with the second character in the search string :

SELECT INSTR('CORPORATE FLOOR','OR', -3, 2) "Reversed Instring"
  FROM DUAL;
 
Reversed Instring
-----------------
                2

The next example assumes a double-byte database character set.

SELECT INSTRB('CORPORATE FLOOR','OR',5,2) "Instring in bytes"
  FROM DUAL;

Instring in bytes
-----------------
               27