LIKE pattern matching in MySQL - Step-by-Step Execution

Concept Flow - LIKE pattern matching

Start with string to match

↓

Apply LIKE pattern

↓

Check each character

↓

Continue

↓

End of string?

↓

Match

The LIKE pattern matching checks a string against a pattern with wildcards, character by character, to find if it matches or not.

Execution Sample

MySQL

SELECT * FROM employees WHERE name LIKE 'J%n';

This query finds all employees whose names start with 'J' and end with 'n', with any characters in between.

Execution Table

Step	String Checked	Pattern Part	Match Result	Action
1	'John'	'J%n'	J matches J	Continue
2	'ohn'	'%n'	% matches 'oh'	Continue
3	'n'	'n'	n matches n	Continue
4	End of string	End of pattern	Full match	Return row
5	'Jason'	'J%n'	J matches J	Continue
6	'ason'	'%n'	% matches 'aso'	Continue
7	'n'	'n'	n matches n	Continue
8	End of string	End of pattern	Full match	Return row
9	'Jim'	'J%n'	J matches J	Continue
10	'im'	'%n'	% matches 'im'	Continue
11	End of string	'n'	No match	Skip row

💡 Stop when string or pattern ends or no match found

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	After Step 9	After Step 10	After Step 11	Final
Current String Position	0	1	3	4	End	0	1	3	4	0	1	End	End
Current Pattern Position	0	1	2	3	End	0	1	2	3	0	1	2	End
Match Status	Pending	Match	Match	Match	Full match	Pending	Match	Match	Full match	Pending	Match	No match	No match

Key Moments - 2 Insights

Why does the '%' wildcard match multiple characters?

Because '%' can match zero or more characters, it allows the pattern to skip over any number of characters in the string, as shown in steps 2 and 6 where '%n' matches 'oh' and 'aso'.

Why does the pattern fail to match 'Jim'?

At step 11, the pattern expects 'n' at the end, but the string ends with 'm', so the match fails as shown in the execution_table row 11.

Visual Quiz - 3 Questions

Look at the execution table, what is the match result at step 6 for string 'Jason'?

A '%n' matches 'as'

B '%n' matches 'son'

C '%n' matches 'aso'

D '%n' matches 'on'

💡 Hint

Check the 'Pattern Part' and 'Match Result' columns at step 6 in the execution_table.

At which step does the pattern fail to match the string 'Jim'?

A Step 9

B Step 11

C Step 10

D Step 12

💡 Hint

Look at the 'Match Result' and 'Action' columns for 'Jim' in the execution_table.

If the pattern was 'J%n' and the string was 'Jan', what would happen at step 2?

A '%n' matches 'an'

B '%n' matches '' (empty string)

C '%n' matches 'a'

D No match

💡 Hint

Remember '%' matches zero or more characters; check how it matched 'ohn' and 'ason' in previous examples.

Concept Snapshot

LIKE pattern matching in SQL:
- '%' matches zero or more characters
- '_' matches exactly one character
- Pattern is matched left to right
- Returns rows where string fits pattern
- Useful for flexible text search

Full Transcript

The LIKE pattern matching in MySQL checks if a string fits a pattern that can include wildcards. The '%' wildcard matches any number of characters, including none, while '_' matches exactly one character. The matching process compares the string and pattern character by character, moving forward when characters match or when '%' allows skipping characters. If the entire pattern matches the string, the row is returned. If a mismatch occurs, the row is skipped. For example, the pattern 'J%n' matches names starting with 'J' and ending with 'n', with anything in between. This is useful for searching text flexibly in databases.