MySQL左外部联接，右表中的列不是外键

Question

My understanding of left outer join is,

table1:
id(pk) name(unique_key) address phone

table2:
    new_id(pk) name(foreign key) company work-experience

1st table:
1 a x 123
2 b y 234
3 c z 345

2nd table
1 a aaa 2
2 a aab 3
3 b aab 3

if I will do,

select * from table1 left outer join table2 on table1.name=table2.name,

it will give me
1 a x 123 1 a aaa 2
1 a x 123 2 a aab 3
2 b y 345 3 b aab 3
3 c z 345 NULL NULL NULL NULL

Now instead of above result, I want to get all the rows where company is aab. Also , for any entry in 1st table, if there is no corresponding entry in 2nd table then it should give me NULL for all columns in 2nd table.

like this:

1 a x 123 aab 3
2 b y 234 aab 3
3 c z 345 NULL NULL

is the above result possible with left outer join ? If not, How can I get the above result ?

Answer 1

You can simply add the conditions for the second table (right-side table), in the ON part of LEFT JOIN .

SELECT * FROM table1 AS t1
LEFT OUTER JOIN table2 AS t2
  ON t1.name = t2.name AND 
     t2.company = 'aab'

Also, in case of multi-table queries, it is advisable to use Aliasing , for code clarity (enhanced readability), and avoiding unambiguous behaviour.

Answer 2

select t1.name,t1.address,t1.phoneNo,t2.comapnay,t2.workExperiance from table1 as t1 left outer join table2 as t2 on t1.name=t2.name AND t2.company = 'aab'