Advanced SQL Topics: ELT Function
Syntax
ELT(n, value1, value2, ..., valueN)
Example
Suppose we have a table named employees with the following columns: employee_id, first_name, last_name, and salary. The table contains the following data:
| employee_id | first_name | last_name | salary |
|---|---|---|---|
| 1 | John | Smith | 50000 |
| 2 | Jane | Doe | 60000 |
| 3 | Adam | Johnson | 70000 |
We can use the ELT function to select the first or nth value from a list:
SELECT ELT(1, first_name, last_name) as name, salary
FROM employees;
Output:
| name | salary |
|---|---|
| John | 50000 |
| Jane | 60000 |
| Adam | 70000 |
SELECT ELT(2, first_name, last_name) as name, salary
FROM employees;
Output:
| name | salary |
|---|---|
| Smith | 50000 |
| Doe | 60000 |
| Johnson | 70000 |
Explanation
The ELT function returns the nth value from a list of values. The first argument is the number of the value to return (an integer). The subsequent arguments are the values to select from. If the first argument is larger than the number of values in the list, the function returns NULL.
Use
The ELT function can be used to select data based on a specific condition or criteria. For example, we can use the ELT function to select the second highest salary from a table of employees:
SELECT last_name, salary
FROM employees
ORDER BY salary DESC
LIMIT 1, 1;
Output:
| last_name | salary |
|---|---|
| Doe | 60000 |
We can also use the ELT function to select values from different columns and concatenate them into a single output value.
Important Points
- The ELT function returns the nth value from a list of values.
- The first argument is the number of the value to return (an integer).
- The subsequent arguments are the values to select from.
- If the first argument is larger than the number of values in the list, the function returns NULL.
Summary
The ELT function is a useful tool in SQL that allows you to select specific values from a list based on position. It is particularly useful when you need to select data based on a specific condition or when you need to concatenate values from different columns into a single output.