LIKE operator

Syntax#

• Wild Card with % : SELECT * FROM [table] WHERE [column_name] Like ‘%Value%’

  Wild Card with _ : SELECT * FROM [table] WHERE [column_name] Like ‘V_n%’

  Wild Card with [charlist] : SELECT * FROM [table] WHERE [column_name] Like ‘V[abc]n%’

Remarks#

LIKE condition in WHERE clause is used to search for column values that matches the given pattern. Patterns are formed using following two wildcard characters

• % (Percentage Symbol) - Used for representing zero or more characters
• _ (Underscore) - Used for representing a single character

Match open-ended pattern

The % wildcard appended to the beginning or end (or both) of a string will allow 0 or more of any character before the beginning or after the end of the pattern to match.

Using ’%’ in the middle will allow 0 or more characters between the two parts of the pattern to match.

We are going to use this Employees Table:

SELECT * FROM Employees WHERE FName LIKE '%on%';

SELECT * FROM Employees WHERE PhoneNumber LIKE '246%';

Following statement matches all records having PhoneNumber ending with string ‘11’ from Employees.

SELECT * FROM Employees WHERE PhoneNumber LIKE '%11'

All records where Fname 3rd character is ‘n’ from Employees.

SELECT * FROM Employees WHERE FName LIKE '__n%';

(two underscores are used before ‘n’ to skip first 2 characters)

Single character match

To broaden the selections of a structured query language (SQL-SELECT) statement, wildcard characters, the percent sign (%) and the underscore (_), can be used.

The _ (underscore) character can be used as a wildcard for any single character in a pattern match.

Find all employees whose Fname start with ‘j’ and end with ‘n’ and has exactly 3 characters in Fname.

SELECT * FROM Employees WHERE FName LIKE 'j_n'

_ (underscore) character can also be used more than once as a wild card to match patterns.

For example, this pattern would match “jon”, “jan”, “jen”, etc.

These names will not be shown “jn”,“john”,“jordan”, “justin”, “jason”, “julian”, “jillian”, “joann” because in our query one underscore is used and it can skip exactly one character, so result must be of 3 character Fname.

For example, this pattern would match “LaSt”, “LoSt”, “HaLt”, etc.

SELECT * FROM Employees WHERE FName LIKE '_A_T'

Match by range or set

Match any single character within the specified range (e.g.: [a-f]) or set (e.g.: [abcdef]).

This range pattern would match “gary” but not “mary”:

SELECT * FROM Employees WHERE FName LIKE '[a-g]ary'

This set pattern would match “mary” but not “gary”:

SELECT * FROM Employees WHERE Fname LIKE '[lmnop]ary'

The range or set can also be negated by appending the ^ caret before the range or set:

This range pattern would not match “gary” but will match “mary”:

SELECT * FROM Employees WHERE FName LIKE '[^a-g]ary'

This set pattern would not match “mary” but will match”gary”:

SELECT * FROM Employees WHERE Fname LIKE '[^lmnop]ary'

Match ANY versus ALL

Match any:
Must match at least one string. In this example the product type must be either ‘electronics’, ‘books’, or ‘video’.

SELECT *
FROM   purchase_table
WHERE  product_type LIKE ANY ('electronics', 'books', 'video');

Match all (must meet all requirements).
In this example both ‘united kingdom’ and ‘london’ and ‘eastern road’ (including variations) must be matched.

SELECT *
FROM   customer_table
WHERE  full_address LIKE ALL ('%united kingdom%', '%london%', '%eastern road%');

Negative selection:
Use ALL to exclude all items.
This example yields all results where the product type is not ‘electronics’ and not ‘books’ and not ‘video’.

SELECT *
FROM   customer_table
WHERE  product_type NOT LIKE ALL ('electronics', 'books', 'video');

Search for a range of characters

Following statement matches all records having FName that starts with a letter from A to F from Employees Table.

SELECT * FROM Employees WHERE FName LIKE '[A-F]%'

ESCAPE statement in the LIKE-query

If you implement a text-search as LIKE-query, you usually do it like this:

SELECT * 
FROM T_Whatever 
WHERE SomeField LIKE CONCAT('%', @in_SearchText, '%') 

However, (apart from the fact that you shouldn’t necessarely use LIKE when you can use fulltext-search) this creates a problem when somebody inputs text like “50%” or “a_b”.

So (instead of switching to fulltext-search), you can solve that problem using the LIKE-escape statement:

SELECT * 
FROM T_Whatever 
WHERE SomeField LIKE CONCAT('%', @in_SearchText, '%') ESCAPE '\'

That means \ will now be treated as ESCAPE character. This means, you can now just prepend \ to every character in the string you search, and the results will start to be correct, even when the user enters a special character like % or _.

e.g.

string stringToSearch = "abc_def 50%";
string newString = "";
foreach(char c in stringToSearch) 
     newString += @"\" + c;
 
sqlCmd.Parameters.Add("@in_SearchText", newString); 
// instead of sqlCmd.Parameters.Add("@in_SearchText", stringToSearch);

Note: The above algorithm is for demonstration purposes only. It will not work in cases where 1 grapheme consists out of several characters (utf-8). e.g. string stringToSearch = "Les Mise\u0301rables"; You’ll need to do this for each grapheme, not for each character. You should not use the above algorithm if you’re dealing with Asian/East-Asian/South-Asian languages. Or rather, if you want correct code to begin with, you should just do that for each graphemeCluster.

See also https://stackoverflow.com/questions/1009689/reversestring-a-c-sharp-interview-question/36312251#36312251

Wildcard characters

wildcard characters are used with the SQL LIKE operator. SQL wildcards are used to search for data within a table.

Wildcards in SQL are:%, _, [charlist], [^charlist]

% - A substitute for zero or more characters

   Eg:  //selects all customers with a City starting with "Lo"
        SELECT * FROM Customers
        WHERE City LIKE 'Lo%';

       //selects all customers with a City containing the pattern "es"
      SELECT * FROM Customers
       WHERE City LIKE '%es%';

_ - A substitute for a single character

Eg://selects all customers with a City starting with any character, followed by "erlin"
SELECT * FROM Customers
WHERE City LIKE '_erlin';

[charlist] - Sets and ranges of characters to match

Eg://selects all customers with a City starting with "a", "d", or "l"
SELECT * FROM Customers
WHERE City LIKE '[adl]%';

//selects all customers with a City starting with "a", "d", or "l"
SELECT * FROM Customers
WHERE City LIKE '[a-c]%';

[^charlist] - Matches only a character NOT specified within the brackets

Eg://selects all customers with a City starting with a character that is not "a", "p", or "l"
SELECT * FROM Customers
WHERE City LIKE '[^apl]%';

or

SELECT * FROM Customers
WHERE City NOT LIKE '[apl]%' and city like '_%';