Parentheses and JOINs? -- MIDRANGE-L

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The recent question on JOINs at IAAI has me thinking - finally! some might say.

What affect do parentheses have on join order? I thought I'd heard that the optimizer pretty much ignores parentheses. The manual is pretty sketchy, at least in this statement:

The order in which multiple joins are performed can affect the result. Joins can be nested within other joins. The order of processing for joins is generally from left to right, but based on the position of the required join-condition. Parentheses are recommended to make the order of nested joins more readable.

Oh, wait, I think I begin to get it. A JOIN is a bracketed clause that starts with JOIN... and ends with ...ON... -- so that you control the nesting by where the ON goes.

Here's the example:

For example:
TB1 LEFT JOIN TB2 ON TB1.C1=TB2.C1
LEFT JOIN TB3 LEFT JOIN TB4 ON TB3.C1=TB4.C1
ON TB1.C1=TB3.C1

is the same as
(TB1 LEFT JOIN TB2 ON TB1.C1=TB2.C1)
LEFT JOIN (TB3 LEFT JOIN TB4 ON TB3.C1=TB4.C1)
ON TB1.C1=TB3.C1

Hmm - verrrry eeenterrresting!

Vern

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