It's about "LEFT JOIN" in SQL query.
I would like to blog it by 4 steps:

1. What's Left Join?
2. How to implement?
3. Common errors.
4. Some practise.

If you are seeking for an answer from internet for what’s going wrong with your SQL left join, you may try luck by directly go to item 3. If you would like learn something about left join, let’s start from the beginning.

1. What's Left Join?
Firstly explain it to a 10 years old boy about what’s left join.
Class you in, some mates have white paper on hands; The next class have some color pens on hands.
Now the teacher is asking you to: find out how many mates in your class with paper already find their partners with a pen, so they can play painting and how many mates left don’t have paper on hands so the teacher could get for them.
Now what are you going to say:
Hey, all of the us please stand in a queue, all of the next door buddies with pens on hands please come here find you partners with paper on hand.
Look, the words you are saying is exactly the “left join” command in SQL try to do, to match staffs from different places.

Secondly explain in programming:
"Select" in SQL is pretty much a function in programming language, with the indicated data sources generate into one & only one output.
The role left join plays here is to ...

tags: sql coding

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