rewriting LEFT JOINs as RIGHT JOINs

#1

Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

#2

yawnmoth wrote:

Quote:

Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You
could do it either way, but what data you get back will be different.
If you do as you say, it is not merely changing the LEFT to a RIGHT, you
are changing the entire SQL query. This can cause unforeseen problems,
particularly speed, temp disk space consumed (some databases are not
smart on data retrieval and caching), and what records are actually
returned.

Thats like saying you can omit the ORs and ANDs and rewrite the SQL as a
SELECT/UNION query. It is not a simple thing and it wastes man hours
and computer time.

#3

yawnmoth wrote:

Quote:

Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You
could do it either way, but what data you get back will be different.
If you do as you say, it is not merely changing the LEFT to a RIGHT, you
are changing the entire SQL query. This can cause unforeseen problems,
particularly speed, temp disk space consumed (some databases are not
smart on data retrieval and caching), and what records are actually
returned.

Thats like saying you can omit the ORs and ANDs and rewrite the SQL as a
SELECT/UNION query. It is not a simple thing and it wastes man hours
and computer time.

#4

yawnmoth wrote:

Quote:

Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You
could do it either way, but what data you get back will be different.
If you do as you say, it is not merely changing the LEFT to a RIGHT, you
are changing the entire SQL query. This can cause unforeseen problems,
particularly speed, temp disk space consumed (some databases are not
smart on data retrieval and caching), and what records are actually
returned.

Thats like saying you can omit the ORs and ANDs and rewrite the SQL as a
SELECT/UNION query. It is not a simple thing and it wastes man hours
and computer time.

#5

Quote:

can every LEFT JOIN be rewritten as a query with RIGHT JOINs?

Sure. Just put the preserved table expression on the RIGHT or LEFT
side of the infixed join operator and leave the ON clause alone. But
since you come from a culture that reads left to right, RIGHT OUTER
JOIN is harder to maintain or to even read.

#6

Quote:

can every LEFT JOIN be rewritten as a query with RIGHT JOINs?

Sure. Just put the preserved table expression on the RIGHT or LEFT
side of the infixed join operator and leave the ON clause alone. But
since you come from a culture that reads left to right, RIGHT OUTER
JOIN is harder to maintain or to even read.

#7

Quote:

can every LEFT JOIN be rewritten as a query with RIGHT JOINs?

Sure. Just put the preserved table expression on the RIGHT or LEFT
side of the infixed join operator and leave the ON clause alone. But
since you come from a culture that reads left to right, RIGHT OUTER
JOIN is harder to maintain or to even read.

#8

"Harry Skelton" <skelton.harry (AT) gmail (DOT) com> wrote

Quote:

yawnmoth wrote:
Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You could
do it either way, but what data you get back will be different. If you do
as you say, it is not merely changing the LEFT to a RIGHT, you are
changing the entire SQL query. This can cause unforeseen problems, [...]
are actually returned.

Total nonsense.

R.

#9

"Harry Skelton" <skelton.harry (AT) gmail (DOT) com> wrote

Quote:

yawnmoth wrote:
Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You could
do it either way, but what data you get back will be different. If you do
as you say, it is not merely changing the LEFT to a RIGHT, you are
changing the entire SQL query. This can cause unforeseen problems, [...]
are actually returned.

Total nonsense.

R.

#10

"Harry Skelton" <skelton.harry (AT) gmail (DOT) com> wrote

Quote:

yawnmoth wrote:
Out of curiosity, can every LEFT JOIN be rewritten as a query with
RIGHT JOINs? It seems to me that if you just take the "leftmost"
table and use that in the FROM part of a SELECT that all subsequent
LEFT JOINs would need to be RIGHT JOINs...

LEFT and RIGHT joins dictate precedence of the tables/queries. You could
do it either way, but what data you get back will be different. If you do
as you say, it is not merely changing the LEFT to a RIGHT, you are
changing the entire SQL query. This can cause unforeseen problems, [...]
are actually returned.

Total nonsense.

R.