MySQL FIRST_VALUE Function

 

MySQL FIRST_VALUE Function


Summary: in this tutorial, you will learn how to use the MySQL FIRST_VALUE() function to get the first row of a frame, partition, or result set.

Overview of the FIRST_VALUE() function

The FIRST_VALUE() is a window function that allows you to select the first row of a window frame, partition, or result set.

The following illustrates the syntax of the FIRST_VALUE() function:

FIRST_VALUE (expression) OVER ( [partition_clause] [order_clause] [frame_clause] )

In this syntax:

expression

The FIRST_VALUE() the function returns the value of the expression from the first row of the window frame.

The OVER clause consists of three clauses: partition_clauseorder_clause, and frame_clause.

partition_clause

The partition_clause clause divides the rows of the result sets into partitions to which the function applies independently. The partition_clause has the following syntax:

PARTITION BY expr1, expr2, ...

order_clause

The order_clause the clause specifies the logical order of rows in each partition on which the FIRST_VALUE() function operates. The following shows the syntax of the order_clause:

ORDER BY expr1 [ASC|DESC], expr2 [ASC|DESC], ...

frame_clause

The frame_clause defines the subset (or frame) of the current partition. For detailed information on the frame clause syntax, check out the window functions tutorial.

MySQL FIRST_VALUE() function examples

The following statements create a new table named overtime and insert sample data for the demonstration:

CREATE TABLE overtime ( employee_name VARCHAR(50) NOT NULL, department VARCHAR(50) NOT NULL, hours INT NOT NULL, PRIMARY KEY (employee_name , department) ); INSERT INTO overtime(employee_name, department, hours) VALUES('Diane Murphy','Accounting',37), ('Mary Patterson','Accounting',74), ('Jeff Firrelli','Accounting',40), ('William Patterson','Finance',58), ('Gerard Bondur','Finance',47), ('Anthony Bow','Finance',66), ('Leslie Jennings','IT',90), ('Leslie Thompson','IT',88), ('Julie Firrelli','Sales',81), ('Steve Patterson','Sales',29), ('Foon Yue Tseng','Sales',65), ('George Vanauf','Marketing',89), ('Loui Bondur','Marketing',49), ('Gerard Hernandez','Marketing',66), ('Pamela Castillo','SCM',96), ('Larry Bott','SCM',100), ('Barry Jones','SCM',65);

1) Using MySQL FIRST_VALUE() function over the whole query result set example

The following statement gets the employee name, overtime, and the employee who has the least overtime:

SELECT employee_name, hours, FIRST_VALUE(employee_name) OVER ( ORDER BY hours ) least_over_time FROM overtime;

Here is the output:

MySQL FIRST_VALUE Function Example

In this example, the ORDER BY clause ordered the rows in the result set by hours and the FIRST_VALUE() picked the first row indicating the employee who had the least over time.

2) Using MySQL FIRST_VALUE() over the partitioning example

The following statement finds the employee who has the least overtime in every department:

SELECT employee_name, department, hours, FIRST_VALUE(employee_name) OVER ( PARTITION BY department ORDER BY hours ) least_over_time FROM overtime;

The output is:

In this example:

  • First, the PARTITION BY clause divided the employees into partitions by departments. In other words, each partition consists of employees who belong to the same department.
  • Second, the ORDER BY clause specified the orders of rows in each partition.
  • Third, the FIRST_VALUE() operates on each partition sorted by the hours. It returned the first row in each partition which is the employee who has the least overtime within the department.

In this tutorial, you have learned how to use the MySQL FIRST_VALUE() function to get the first row of a window frame.

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