Comparison of Mysql’s Left Join and Left Outer Join

The > and < operators, as well as the + and - operators, along with numerous logical operators, function similarly. However, the effectiveness of each operator likely varies depending on factors such as data characteristics, accessible indexes, and other relevant factors.


Solution 1:

Like any other performance-related query, it is important to evaluate the outcomes on your specific data and systems. The functions

union

and

left join

have distinct functionalities, and determining which one is superior largely depends on the specific characteristics of your data, the presence of indexes, and other relevant factors.

Nevertheless, by utilizing the

union

technique within

update

, a subquery is all that is required.

update t join
       (select t.id, t1.foo . . .
        union . . . 
        select t.id, t2.foo
       ) tt
       on t.id = tt.id
    set t.foo = 'foo'
    where . . .;

Consider utilizing the

union

approach for increased efficiency, while dividing the update into multiple distinct

update

statements.


Solution 2:


The inclusion of

UNION

is possible in inserts.

INSERT INTO `table`
SELECT * FROM   
(
    SELECT '1'
    UNION
    SELECT '2'
) x

Same goes for updates:

UPDATE `table1` t1
JOIN (
    SELECT '1' as col1
    UNION
    SELECT '2'
) x ON x.col1 = t1.colX  
SET t1.whateverColumn = "someValue"

In terms of performance, it largely depends on indexes. Both options can exhibit speed or slowness. When properly indexed, significant disparities between the two should not be noticeable.

Frequently Asked Questions