How to fix ERROR 1072: Key column doesn't exist in table in MySQL

DESCRIBE your_table_name;
-- or
SHOW COLUMNS FROM your_table_name;

-- Wrong - typo in column name
CREATE INDEX idx_email ON users(emial);

-- Correct - exact column name match
CREATE INDEX idx_email ON users(email);

-- First, add the missing column
ALTER TABLE your_table_name ADD COLUMN column_name VARCHAR(255);

-- Then, create the index or key
ALTER TABLE your_table_name ADD INDEX idx_name (column_name);

-- First, create the parent table
CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);

-- Then create the child table with the foreign key
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department_id INT,
  FOREIGN KEY (department_id) REFERENCES departments(id)
);

-- Correct - foreign key matches the index definition order
CREATE TABLE navigation (
  nav_location VARCHAR(100),
  user_id INT,
  PRIMARY KEY (nav_location, user_id)
);

CREATE TABLE user_navigation (
  nav_location VARCHAR(100),
  user_id INT,
  FOREIGN KEY (nav_location, user_id) REFERENCES navigation(nav_location, user_id)
);

-- Wrong - column order doesn't match
-- FOREIGN KEY (user_id, nav_location) would cause error if index is (nav_location, user_id)