mysql query and illegal scalar sub-queries

#where or behind HAVING:
# scalar query (single subquery)
# column subquery (multiple-row subqueries)
# subquery row (rows and columns)

Features: subquery placed in parentheses, the general conditions on the right side, a single row with general scalar query operator using
a single line operator: <>> = <= <>
column subquery: Usually a plurality of rows with the operator using
multi-line operator: in, any, some, all

# Scalar subquery
# Case: Who wages higher than the employee information ABEL

SELECT *
FROM  employees
WHERE salary>(

    SELECT salary
    FROM employees
    WHERE last_name='Abel'
);

Case #: job_id returned with the same number of 141 employees, salary of employees more than the employee's name No. 143, job_id and wages

SELECT
    last_name,job_id,salary
FROM employees
WHERE job_id=(
    SELECT job_id
    FROM employees
    WHERE employee_id=141
)
AND salary>(
    SELECT salary
    FROM employees
    WHERE employee_id=143
);

Case #: return last_name minimum wage employees, job_id, and salary

SELECT  last_name,job_id,salary
FROM employees
WHERE   salary=(
    SELECT MIN(salary)
    FROM employees
);

Case #: Query No. 50 is greater than the minimum wage sector minimum wage and the minimum wage department id

SELECT department_id,MIN(salary)
FROM employees
GROUP BY department_id
HAVING  MIN(salary)>(
    SELECT MIN(salary)
    FROM employees
    WHERE department_id=50
);

# Unlawful use of standard quantum query

SELECT department_id,MIN(salary)
FROM employees
GROUP BY department_id
HAVING  MIN(salary)>(
    SELECT salary   #单行操作符只能搭配标量子查询，而这是列子查询
    FROM employees
    WHERE department_id=50
);