6df0cb92fb
* Included use of underscore wildcard character Included the use and example of wildcard character underscore which can be used with LIKE operator * fix(guide): minor typos and grammar
127 lines
5.8 KiB
Markdown
127 lines
5.8 KiB
Markdown
---
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title: SQL LIKE Operator
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---
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## SQL LIKE Operator
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### LIKE Operator defined
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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
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### ILIKE Opeartor
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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`.
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For Example,
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```sql
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FullName LIKE 'monique%' // --you will face error because the name saved in Database is 'Monique'.
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FullName ILIKE 'monique%' // --you will not see any error now.
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```
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### This guide will demonstrate:
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* Determining if a string starts or ends with a given string pattern
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* Determining if a pattern exists in the middle of the string
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* Determining if a string is not contained in the string
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* Determining if a string is has specified letter at any position in the string
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### A column starts or ends with a given string pattern
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This SQL will select students that have `FullName` starting with "Monique" or ending with "Greene".
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Here **%** means that it can be replaced by any number of characters.
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```sql
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SELECT studentID, FullName, sat_score, rcd_updated
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FROM student
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WHERE
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FullName LIKE 'Monique%' OR -- note the % at the end but not the beginning
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FullName LIKE '%Greene'; -- note the % at the beginning but not the end
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```
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```text
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+-----------+---------------+-----------+---------------------+
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| studentID | FullName | sat_score | rcd_updated |
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+-----------+---------------+-----------+---------------------+
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| 1 | Monique Davis | 400 | 2017-08-16 15:34:50 |
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| 5 | Alvin Greene | 1200 | 2017-08-16 15:34:50 |
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+-----------+---------------+-----------+---------------------+
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2 rows in set (0.00 sec)
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```
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### A string pattern is in the middle of the column
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This SQL will select students that have "ree" anywhere in the name.
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```sql
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SELECT studentID, FullName, sat_score, rcd_updated
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FROM student
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WHERE FullName LIKE '%ree%'; -- note the % at the beginning AND at the end
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```
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```text
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+-----------+----------------+-----------+---------------------+
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| studentID | FullName | sat_score | rcd_updated |
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+-----------+----------------+-----------+---------------------+
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| 5 | Alvin Greene | 1200 | 2017-08-16 15:34:50 |
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| 6 | Sophie Freeman | 1200 | 2017-08-16 15:34:50 |
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+-----------+----------------+-----------+---------------------+
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2 rows in set (0.00 sec)
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```
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### A string is NOT in the column
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You can place "NOT" before LIKE to exclude the rows with the string pattern instead of selecting them.
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This SQL excludes records that contain "cer Pau" and "Ted" in the FullName column.
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```sql
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SELECT studentID, FullName, sat_score, rcd_updated
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FROM student
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WHERE FullName NOT LIKE '%cer Pau%' AND FullName NOT LIKE '%"Ted"%';
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```
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```text
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+-----------+----------------------+-----------+---------------------+
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| studentID | FullName | sat_score | rcd_updated |
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+-----------+----------------------+-----------+---------------------+
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| 1 | Monique Davis | 400 | 2017-08-16 15:34:50 |
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| 2 | Teri Gutierrez | 800 | 2017-08-16 15:34:50 |
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| 4 | Louis Ramsey | 1200 | 2017-08-16 15:34:50 |
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| 5 | Alvin Greene | 1200 | 2017-08-16 15:34:50 |
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| 6 | Sophie Freeman | 1200 | 2017-08-16 15:34:50 |
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| 8 | Donald D. Chamberlin | 2400 | 2017-08-16 15:35:33 |
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| 9 | Raymond F. Boyce | 2400 | 2017-08-16 15:35:33 |
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+-----------+----------------------+-----------+---------------------+
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7 rows in set (0.00 sec)
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```
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### A string has a specific letter say o in the second position
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This SQL shows records having **o** as the alphabet in second position in the FullName column.
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Here **_** means that it can be replaced by only a single character.
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```sql
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SELECT studentID, FullName, sat_score, rcd_updated
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FROM student
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WHERE FullName LIKE '_o%';
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```
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```text
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+-----------+----------------------+-----------+---------------------+
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| studentID | FullName | sat_score | rcd_updated |
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+-----------+----------------------+-----------+---------------------+
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| 1 | Monique Davis | 400 | 2017-08-16 15:34:50 |
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| 4 | Louis Ramsey | 1200 | 2017-08-16 15:34:50 |
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| 6 | Sophie Freeman | 1200 | 2017-08-16 15:34:50 |
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| 8 | Donald D. Chamberlin | 2400 | 2017-08-16 15:35:33 |
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+-----------+----------------------+-----------+---------------------+
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4 rows in set (0.00 sec)
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```
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*Here is the current full student list to compare to the where clause result sets above.*
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```sql
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SELECT studentID, FullName, sat_score, rcd_updated FROM student;
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```
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```text
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+-----------+------------------------+-----------+---------------------+
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| studentID | FullName | sat_score | rcd_updated |
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+-----------+------------------------+-----------+---------------------+
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| 1 | Monique Davis | 400 | 2017-08-16 15:34:50 |
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| 2 | Teri Gutierrez | 800 | 2017-08-16 15:34:50 |
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| 3 | Spencer Pautier | 1000 | 2017-08-16 15:34:50 |
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| 4 | Louis Ramsey | 1200 | 2017-08-16 15:34:50 |
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| 5 | Alvin Greene | 1200 | 2017-08-16 15:34:50 |
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| 6 | Sophie Freeman | 1200 | 2017-08-16 15:34:50 |
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| 7 | Edgar Frank "Ted" Codd | 2400 | 2017-08-16 15:35:33 |
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| 8 | Donald D. Chamberlin | 2400 | 2017-08-16 15:35:33 |
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| 9 | Raymond F. Boyce | 2400 | 2017-08-16 15:35:33 |
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+-----------+------------------------+-----------+---------------------+
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9 rows in set (0.00 sec)
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