LIKE Operator FAQS

1. What is the purpose of the LIKE operator in Oracle?

• The LIKE operator is used to search for a specified pattern in a column. 
• It allows partial string matching in a query, enabling users to search for strings that match a specific format, rather than exact values.

 

2. How do wildcards work with the LIKE operator?

• The LIKE operator uses two main wildcards:
• %: Represents zero, one, or multiple characters.
• _: Represents a single character.

Examples:

• LIKE 'S%' matches any string starting with "S".
• LIKE '_r_wn' matches any string with four characters where the second character is "r" and the third is "w".

 

3. Is the LIKE operator case-sensitive?

• By default, the LIKE operator in Oracle is case-insensitive.
• However, if you need to perform case-sensitive searches, you can use the UPPER or LOWER functions to ensure consistency.

Example (case-insensitive):

SELECT * FROM employees

WHERE last_name LIKE 'smith';  -- This matches 'Smith', 'SMITH', etc.

Example (case-sensitive):

SELECT * FROM employees

WHERE UPPER(last_name) LIKE 'SMITH';  -- Matches only 'SMITH'

 

4. Can I use LIKE with numbers?

• Yes, you can use LIKE with numeric columns by converting them to strings.
• For instance, you can match numeric values that follow a certain pattern.

Example:

SELECT * FROM orders

WHERE order_number LIKE '100%';  -- Matches order numbers starting with '100'

 

5. What is the difference between LIKE and REGEXP_LIKE?

• While LIKE provides basic pattern matching (with % and _), REGEXP_LIKE allows more advanced regular expression pattern matching, which provides greater flexibility and complexity in search patterns.

Example:

SELECT * FROM employees

WHERE REGEXP_LIKE(last_name, '^S.*h$');  -- Matches names that start with 'S' and end with 'h'

 

6. Can I use LIKE with dates?

• Yes, you can use LIKE with dates, but you'll need to convert the date to a string using the TO_CHAR function.

Example:

SELECT * FROM orders

WHERE TO_CHAR(order_date, 'YYYY-MM-DD') LIKE '2021-08%';  -- Matches orders from August 2021

 

7. How do I perform a negated LIKE search?

• To search for rows where the column value does not match a specified pattern, use NOT LIKE.

Example:

SELECT * FROM employees

WHERE last_name NOT LIKE 'S%';  -- Returns employees whose last name does not start with 'S'

 

8. Can I use LIKE with partial strings?

• Yes, the LIKE operator is commonly used for partial string matching.
• It is useful when you want to find rows that contain a specific sequence of characters anywhere in a string.

Example:

SELECT * FROM products

WHERE product_name LIKE '%phone%';  -- Matches product names containing 'phone'

 

9. Can LIKE be used with multiple patterns?

• Oracle does not support combining multiple patterns directly within a single LIKE condition.
• However, you can use the OR operator to combine multiple LIKE conditions.

Example:

SELECT * FROM employees

WHERE last_name LIKE 'S%' OR last_name LIKE 'J%';  -- Matches names starting with 'S' or 'J'

 

10. What are some performance considerations with the LIKE operator?

• Using the LIKE operator with a leading % (e.g., LIKE '%word%') can cause performance issues, as it prevents the database from using indexes efficiently.
• This leads to full table scans. Try to avoid % at the start of the pattern if possible.
• Indexes and performance: The LIKE operator is faster when the pattern starts with a fixed string (e.g., LIKE 'abc%'), as it can use indexes to speed up the search.

 

11. How do I use LIKE with wildcard characters in a string?

• If you need to search for the wildcard characters (% or _) as part of the string (not as wildcards), you can escape them using the ESCAPE keyword.

Example:

SELECT * FROM products

WHERE product_name LIKE '%\%%' ESCAPE '\';  -- Matches product names containing the '%' character

 

12. Can I use LIKE for pattern matching on multiple columns?

• While the LIKE operator works for individual columns, if you want to match patterns across multiple columns, you would typically use multiple LIKE conditions combined with AND or OR.

Example:

SELECT * FROM employees

WHERE first_name LIKE 'A%' AND last_name LIKE 'S%';  -- Matches first name starting with 'A' and last name starting with 'S'

 

13. Does LIKE support regex or regular expressions?

• No, LIKE is not as powerful as regular expressions.
• If you need more complex pattern matching, consider using REGEXP_LIKE in Oracle, which allows for regular expressions to match a pattern with more flexibility.

 

14. Can LIKE be used for numeric columns?

• Although LIKE is primarily designed for string matching, it can be used with numeric columns by converting them into strings.
• However, for performance reasons, it's better to avoid using LIKE with large numeric values.

Example:

SELECT * FROM employees

WHERE TO_CHAR(salary) LIKE '500%';  -- Matches salaries starting with '500'

 

15. Is LIKE case-sensitive in Oracle by default?

• No, LIKE is case-insensitive by default in Oracle. If you want a case-sensitive search, you can use the UPPER or LOWER function to standardize the case.

Example (case-insensitive):

SELECT * FROM employees

WHERE last_name LIKE 'smith';  -- Matches 'Smith', 'SMITH', 'smIth', etc.

Example (case-sensitive):

SELECT * FROM employees

WHERE UPPER(last_name) LIKE 'SMITH';  -- Matches only 'SMITH'