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What is outer join in MySql

It is used to preserve the missing information resulting from natural join.

R1 table

A           B           C

X           10         100

Y           20         100

Z           30         200

S           40         400

R2 table

C           D

100        L

200        M

300        N

100        T

Missing element in natural join.

Left outer join

Natural Join + Missing information LHS

Output

A       B       C       D

X       10     100      L

Y       20     100     L

Z       30      200     M

X       10     100      T

Y       20     100     T

S       40      400    -

Right outer join

Natural Join + Missing information RHS

Output

A       B       C       D

X       10     100      L

Y       20     100     L

Z       30      200     M

X       10     100      T

Y       20     100     T

-         -       300    N

Full outer join

Natural Join + Missing information LHS + Missing information RHS

Output

A       B       C       D

X       10     100      L

Y       20     100     L

Z       30      200     M

X       10     100      T

Y       20     100     T

-         -       300    N

S       40      400    -

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