This occurs when a column is used in an incorrect context in an SQL query. This error is common when a column name is mistakenly used as a value in an INSERT statement or a constant in a SELECT clause. Here are some possible reasons for this error and ways to solve it with example codes.
1. Using a column name instead of a value in an INSERT
Incorrect Code:
INSERT INTO employees (employee_id, first_name, last_name)
VALUES (employee_id, 'John', 'Doe');Correct Code:
INSERT INTO employees (employee_id, first_name, last_name)
VALUES (1, 'John', 'Doe');Replace the column name (employee_id) with a valid value (1) in the VALUES clause.
2. Using a column name as a constant in a SELECT
Incorrect Code:
SELECT employee_id, first_name, last_name, salary * 1.1 AS new_salary
FROM employees
WHERE salary > employee_id;Correct Code:
SELECT employee_id, first_name, last_name, salary * 1.1 AS new_salary
FROM employees
WHERE salary > 1000;Replace the column name (employee_id) with a valid constant value (1000) in the WHERE clause.
3. Using an invalid alias in a SELECT
Incorrect Code:
SELECT e.employee_id, d.department_name
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_name = department_name;Correct Code:
SELECT e.employee_id, d.department_name
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_name = 'Sales';Replace the column name (department_name) with a valid value (‘Sales’) in the WHERE clause.
4. Using column names in place of expressions in a GROUP BY
Incorrect Code:
SELECT department_id, COUNT(employee_id)
FROM employees
GROUP BY department_id HAVING COUNT(employee_id) > employee_id;Correct Code:
SELECT department_id, COUNT(employee_id)
FROM employees
GROUP BY department_id HAVING COUNT(employee_id) > 5;Replace the column name (employee_id) with a valid value (5) in the HAVING clause.
In summary, always double-check your SQL queries for proper use of column names and constants, and ensure you are using them in the correct context.