MySQL Coalesce

In this section, you will learn about MySQL Coalesce. It selects the first non-null value of its arguments.

Syntax:
coalesce(value,..): It returns the first non NULL value in the list. If there are no non-NULL values then it returns NULL.

Table: employee

CREATE TABLE `employee` (
`emp_id` int(11) NOT NULL auto_increment,
`emp_name` varchar(100) character set utf8 NOT NULL, `emp_salary` int(11) NOT NULL,
`emp_startDate` datetime NOT NULL,
`dep_name` varchar(50) NOT NULL, PRIMARY KEY (`emp_id`)
)

employee table data:

Table: empleavedetails

CREATE TABLE `empleavedetails` (
`id` int(11) NOT NULL auto_increment,
`emp_id` int(11) NOT NULL,
`no_of_leave` int(11) NOT NULL,
PRIMARY KEY (`id`)
)

empleavedetails table data:

Query:

select e.emp_name as Name, l.no_of_leave as NOL from employee e left outer join empleavedetails l on e.emp_id=l.emp_id;

Output: The output contains NULL values in the result list as shown below:

The null values are eliminated from the list using COALESCE. For example:

Query:

select e.emp_name as Name,COALESCE(l.no_of_leave,0) as NOL from employee e left outer join empleavedetails l on e.emp_id=l.emp_id;

Output:

MySQL Coalesce

MySQL Coalesce

MySQL Coalesce

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