MySql Query: Left Join

Question

I am new Sql Queries.I wanted to make a table from difference of two tables.
Here's my query:

SELECT * FROM `question` WHERE `relatedFields` = 'Math' LEFT JOIN  `answer` ON `question`.ques = `answer`.ques where `answer`.TeacherNumber=1111111111

Please help.

Answer 1

Move the first WHERE clause to the end, and move that other where condition to ON to get true LEFT JOIN:

SELECT *
FROM `question`
  LEFT JOIN  `answer` ON `question`.ques = `answer`.ques
     and `answer`.TeacherNumber=1111111111
where `question`.relatedFields = 'Math'

Alternative syntax:

SELECT *
FROM
    (select * from `question` WHERE `relatedFields` = 'Math') as q
LEFT JOIN
    (select * from `answer` where TeacherNumber = 1111111111) as a
  ON q.ques = a.ques

Answer 2

This post will help you to understand better the joins. It help me too.

Explanation about Joins click here.