INSTR

The INSTR function in Oracle SQL is used to find the position of a substring within a string. It returns the position of the first occurrence of the substring, starting from a specified position in the string. If the substring is not found, it returns 0. The function is useful for string searching and can be combined with other string manipulation functions for more advanced text processing.

 

1. Syntax of the INSTR Function

The basic syntax of the INSTR function is:

INSTR(string, substring, start_position, match_occurance)

• string: The string or column to search within.
• substring: The substring to search for within the string.
• start_position (Optional): The position in the string to start searching from. The default value is 1, meaning it starts searching from the beginning of the string. If you want to start from the end, use a negative value.
• match_occurance (Optional): The occurrence of the substring to find. The default value is 1, meaning it searches for the first occurrence. If you want to find subsequent occurrences, specify the occurrence number.

 

2. Default Behavior of INSTR

The INSTR function returns the position of the first occurrence of the substring within the string. If the substring is found, it returns the starting position (1-based index). If the substring is not found, it returns 0.

Example:

SELECT INSTR('Hello World', 'World') FROM dual;

Output: 7
Explanation: The substring World starts at position 7 in the string Hello World.

 

3. Using INSTR with a Start Position

You can specify a starting position for the search. By default, it starts at the beginning of the string, but you can change this to start searching from a specific character.

Example:

SELECT INSTR('Hello World', 'o', 5) FROM dual;

Output: 8
Explanation: This searches for the first occurrence of o starting from position 5, which is at position 8 in Hello World.

 

4. Finding Multiple Occurrences Using INSTR

The match_occurance argument can be used to find the N-th occurrence of the substring.

Example:

SELECT INSTR('Hello World, Hello Universe', 'Hello', 1, 2) FROM dual;

Output: 14
Explanation: This searches for the second occurrence of Hello in the string Hello World, Hello Universe. The second occurrence starts at position 14.

 

5. Using Negative Start Position

You can also search from the end of the string by specifying a negative value for the start_position. This makes INSTR start searching from the right end of the string, which is useful for finding the last occurrence of a substring.

Example:

SELECT INSTR('Hello World, Hello Universe', 'Hello', -1) FROM dual;

Output: 14
Explanation: This searches for the last occurrence of Hello in the string, starting from the end. It finds Hello at position 14 in Hello Universe.

 

6. INSTR with Case Sensitivity

The INSTR function is case-sensitive. It will only match substrings that have the exact same case.

Example:

SELECT INSTR('Hello World', 'world') FROM dual;

Output: 0
Explanation: Since INSTR is case-sensitive and world is not the same as World, it returns 0, indicating that no match was found.

 

7. Using INSTR with NULL Values

If any of the arguments (string, substring, or start_position) are NULL, the INSTR function will return NULL.

Example:

SELECT INSTR(NULL, 'World') FROM dual;

Output: NULL
Explanation: The result is NULL because the first argument is NULL.

 

8. Performance Considerations

• Indexes: If you are using INSTR on a column in a table, the query might not take advantage of indexes, which can affect performance, especially for large datasets.
• Efficiency: While INSTR is a relatively fast function, applying it on large strings or columns with many rows might slow down the query performance. Indexing or more efficient data structures could be considered if performance becomes a concern.

 

9. Example Queries Using INSTR

• Example 1: Finding the position of a substring:

SELECT INSTR('Hello World', 'World') FROM dual;

Output: 7 (Position of World in the string Hello World).

• Example 2: Finding the position of a character starting from a specific position:

SELECT INSTR('Hello World', 'o', 5) FROM dual;

Output: 8 (Position of o after the 5th character in Hello World).

• Example 3: Finding the second occurrence of a substring:

SELECT INSTR('Hello World, Hello Universe', 'Hello', 1, 2) FROM dual;

Output: 14 (Position of the second occurrence of Hello).

• Example 4: Searching from the end of the string:

SELECT INSTR('Hello World, Hello Universe', 'Hello', -1) FROM dual;

Output: 14 (Last occurrence of Hello).

 

10. Combining INSTR with Other Functions

You can use INSTR in combination with other SQL functions such as SUBSTR, REPLACE, or REGEXP_INSTR for more complex string manipulations.

Example:

SELECT SUBSTR('Hello World', INSTR('Hello World', 'World')) FROM dual;

Output: World
Explanation: This extracts the substring starting from the position of World in the string Hello World.

 

11. Common Use Cases for INSTR

1.     Finding the position of a substring:

• It helps you locate where a substring starts within a string, which can be useful for string manipulation or data extraction.

2.     Determining if a substring exists:

• If INSTR returns 0, the substring doesn't exist in the string, which is helpful in conditional checks.

3.     Parsing Strings:

• By using the position of substrings, INSTR can help you extract or manipulate parts of a string (using SUBSTR, for example).

 

FAQs about the INSTR Function

1. Can INSTR be used to find the position of a character in a string?

• Yes, INSTR can be used to find the position of a single character, just as it is used for finding substrings. You can specify a single character in the substring argument, and INSTR will return the position of that character.

2. Can I find all occurrences of a substring with INSTR?

• No, INSTR only finds the first occurrence. However, by using the match_occurance parameter, you can find specific occurrences (e.g., the second or third occurrence). For all occurrences, you would need to repeatedly use INSTR or combine it with a loop or recursive query.

3. Is INSTR case-sensitive?

• Yes, INSTR is case-sensitive. To perform a case-insensitive search, you can either use UPPER or LOWER on both the string and substring arguments or use REGEXP_INSTR with the i flag for case-insensitivity.

4. What happens if the substring is not found?

• If the substring is not found, INSTR will return 0.

5. Can I use INSTR with wildcards or patterns?

• No, INSTR does not support wildcards or patterns. However, REGEXP_INSTR can be used to perform pattern matching with regular expressions.

 

12. Conclusion

The INSTR function in Oracle SQL is a powerful tool for finding the position of substrings within strings. It is useful for searching, parsing, and manipulating strings based on the positions of specific text patterns. By combining INSTR with other string functions like SUBSTR, REPLACE, and TRIM, you can perform complex string operations efficiently.