PostgreSQL - Wildcards

The PostgreSQL wildcard character is used to specify one or more character in a string. It is used with LIKE clause and WHERE clause to search for a specified pattern.

Wildcard Characters in PostgreSQL

Symbol	Description	Example
%	Represents zero, one or multiple characters.	'J%' represents a value that start with "J", for example - John, Jo and Jack etc.
_	Represents one character.	'_o%' represents a value that have "o" in the second position, for example - John, Jo and Journey etc.
ESCAPE	Allow test for literal instances of a wildcard character such as % or _	'J%!%' ESCAPE '!' represents a value that starts with J and ends in %, for example - John%, Jo% and Journey% etc.

The table below describes patterns which is used with LIKE operator and uses (%) and (_).

Pattern	Description
'J%'	A value that start with "J".
'%n'	A value that end with "n".
'%oh%'	A value that have "oh" in any position.
'_o%'	A value that have "o" in the second position.
'J_%'	A value that start with "J" and have at least 2 characters.
'J__%'	A value that start with "J" and have at least 3 characters.
'J%n'	A value that start with "J" and ends with "n".

Example:

Consider a database containing a table called Employee with the following records:

EmpID	Name	City	Age	Salary
1	John	London	25	3000
2	Marry	New York	24	2750
3	Jo	Paris	27	2800
4	Kim	Amsterdam	30	3100
5	Ramesh	New Delhi	28	3000
6	Huang	Beijing	28	2800

Using the % Wildcard : To select all records of the Employee table with Name starting with 'Jo', the query is given below.
```
SELECT * FROM Employee
WHERE Name LIKE 'Jo%';
```
This will produce the result as shown below:

EmpID Name City Age Salary

1 John London 25 3000

3 Jo Paris 27 2800
Using the % Wildcard with NOT LIKE operator: NOT LIKE operator is used as the negation of LIKE operator. For example, to select all records of the Employee table with Name not starting with 'Jo', the following query can be used:
```
SELECT * FROM Employee
WHERE Name NOT LIKE 'Jo%';
```
This will produce the result as shown below:

EmpID Name City Age Salary

2 Marry New York 24 2750

4 Kim Amsterdam 30 3100

5 Ramesh New Delhi 28 3000

6 Huang Beijing 28 2800
Using the _ Wildcard : To select all records of the Employee table with Name containing 'o' as second character, the query is mentioned below.
```
SELECT * FROM Employee
WHERE Name LIKE '_o%';
```
The result of the above code will be:

EmpID Name City Age Salary

1 John London 25 3000

3 Jo Paris 27 2800