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SQL LIKE Operator

SQL LIKE Operator

LIKE Operator defined

The LIKE operator is used in a WHERE or HAVING (as part of the GROUP BY) to limit the selected rows to the items when a column has a certain pattern of characters contained in it. It is used along with two wildcard characters namely underscore _ and percent % symbol

ILIKE Opeartor

The 'ILIKE' works same as 'LIKE' but it ignores case-sensitivity in the string. The provided pattern string should be the case-sensitive else you will get an error. To avoid these errors, just write ILIKE instead of LIKE. For Example,

FullName LIKE 'monique%'                   // --you will face error because the name saved in Database is 'Monique'.
FullName ILIKE 'monique%'                  // --you will not see any error now.

This guide will demonstrate:

Determining if a string starts or ends with a given string pattern
Determining if a pattern exists in the middle of the string
Determining if a string is not contained in the string
Determining if a string is has specified letter at any position in the string

A column starts or ends with a given string pattern

This SQL will select students that have FullName starting with "Monique" or ending with "Greene". Here % means that it can be replaced by any number of characters.

SELECT studentID, FullName, sat_score, rcd_updated
FROM student 
WHERE 
FullName LIKE 'Monique%' OR -- note the % at the end but not the beginning
FullName LIKE '%Greene'; -- note the % at the beginning but not the end

+-----------+---------------+-----------+---------------------+
| studentID | FullName      | sat_score | rcd_updated         |
+-----------+---------------+-----------+---------------------+
|         1 | Monique Davis |       400 | 2017-08-16 15:34:50 |
|         5 | Alvin Greene  |      1200 | 2017-08-16 15:34:50 |
+-----------+---------------+-----------+---------------------+
2 rows in set (0.00 sec)

A string pattern is in the middle of the column

This SQL will select students that have "ree" anywhere in the name.

SELECT studentID, FullName, sat_score, rcd_updated
FROM student 
WHERE FullName LIKE '%ree%'; -- note the % at the beginning AND at the end

+-----------+----------------+-----------+---------------------+
| studentID | FullName       | sat_score | rcd_updated         |
+-----------+----------------+-----------+---------------------+
|         5 | Alvin Greene   |      1200 | 2017-08-16 15:34:50 |
|         6 | Sophie Freeman |      1200 | 2017-08-16 15:34:50 |
+-----------+----------------+-----------+---------------------+
2 rows in set (0.00 sec)

A string is NOT in the column

You can place "NOT" before LIKE to exclude the rows with the string pattern instead of selecting them. This SQL excludes records that contain "cer Pau" and "Ted" in the FullName column.

SELECT studentID, FullName, sat_score, rcd_updated
FROM student 
WHERE FullName NOT LIKE '%cer Pau%' AND FullName NOT LIKE '%"Ted"%';

+-----------+----------------------+-----------+---------------------+
| studentID | FullName             | sat_score | rcd_updated         |
+-----------+----------------------+-----------+---------------------+
|         1 | Monique Davis        |       400 | 2017-08-16 15:34:50 |
|         2 | Teri Gutierrez       |       800 | 2017-08-16 15:34:50 |
|         4 | Louis Ramsey         |      1200 | 2017-08-16 15:34:50 |
|         5 | Alvin Greene         |      1200 | 2017-08-16 15:34:50 |
|         6 | Sophie Freeman       |      1200 | 2017-08-16 15:34:50 |
|         8 | Donald D. Chamberlin |      2400 | 2017-08-16 15:35:33 |
|         9 | Raymond F. Boyce     |      2400 | 2017-08-16 15:35:33 |
+-----------+----------------------+-----------+---------------------+
7 rows in set (0.00 sec)

A string has a specific letter say o in the second position

This SQL shows records having o as the alphabet in second position in the FullName column. Here _ means that it can be replaced by only a single character.

SELECT studentID, FullName, sat_score, rcd_updated
FROM student 
WHERE FullName LIKE '_o%';

+-----------+----------------------+-----------+---------------------+
| studentID | FullName             | sat_score | rcd_updated         |
+-----------+----------------------+-----------+---------------------+
|         1 | Monique Davis        |       400 | 2017-08-16 15:34:50 |
|         4 | Louis Ramsey         |      1200 | 2017-08-16 15:34:50 |
|         6 | Sophie Freeman       |      1200 | 2017-08-16 15:34:50 |
|         8 | Donald D. Chamberlin |      2400 | 2017-08-16 15:35:33 |
+-----------+----------------------+-----------+---------------------+
4 rows in set (0.00 sec)

Here is the current full student list to compare to the where clause result sets above.

SELECT studentID, FullName, sat_score, rcd_updated FROM student;

+-----------+------------------------+-----------+---------------------+
| studentID | FullName               | sat_score | rcd_updated         |
+-----------+------------------------+-----------+---------------------+
|         1 | Monique Davis          |       400 | 2017-08-16 15:34:50 |
|         2 | Teri Gutierrez         |       800 | 2017-08-16 15:34:50 |
|         3 | Spencer Pautier        |      1000 | 2017-08-16 15:34:50 |
|         4 | Louis Ramsey           |      1200 | 2017-08-16 15:34:50 |
|         5 | Alvin Greene           |      1200 | 2017-08-16 15:34:50 |
|         6 | Sophie Freeman         |      1200 | 2017-08-16 15:34:50 |
|         7 | Edgar Frank "Ted" Codd |      2400 | 2017-08-16 15:35:33 |
|         8 | Donald D. Chamberlin   |      2400 | 2017-08-16 15:35:33 |
|         9 | Raymond F. Boyce       |      2400 | 2017-08-16 15:35:33 |
+-----------+------------------------+-----------+---------------------+
9 rows in set (0.00 sec)

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