What is the order of operations

Where can I find the order of operations that are evaluated by the Oracle database? I mean, for example, for a query like this:

Select an element, rank on (partition of order in...) r

from t1, t2

where t1.x = t2.x

and t2.other_something = 'value '.

order by 1;

We can say that: "order by" going to last, "rank" works on lines after that the paintings are "United" and "selected". So in a sense, there is an order of operations. I understand that the actual order of operations when execution can be different if optimizer concludes on an equivalent, alternative execution plan. But what is a sort of operations of op "basic" order Oracle follows "to understand" the request even before trying to understand the alternative form. Is there such a list of order of operations?

Thank you

Hello

946279 wrote:

Where can I find the order of operations that are evaluated by the Oracle database? I mean, for example, for a query like this:

Select an element, rank on (partition of order in...) r

from t1, t2

where t1.x = t2.x

and t2.other_something = 'value '.

order by 1;

We can say that: "order by" going to last, "rank" works on lines after that the paintings are "United" and "selected". So in a sense, there is an order of operations. I understand that the actual order of operations when execution can be different if optimizer concludes on an equivalent, alternative execution plan. But what is a sort of operations of op "basic" order Oracle follows "to understand" the request even before trying to understand the alternative form. Is there such a list of operations?

Thank you

No, I've never seen any kind of official list like that, no doubt because, as you say, the optimizer does not follow these rules; the optimizer has done what he thinks is the fastest way to get the results that you specified.

It may be useful to imagine things in the following order:

  1. Subqueries
  2. Joins (including the join in the WHERE clause conditions)
  3. PIVOT and UNPIVOT
  4. START WITH and CONNECT BY clauses
  5. WHERE clause
  6. Clause GROUP BY and aggregate functions
  7. HAVING clause
  8. Analytic functions (for example, RANK)
  9. ORDER BY clause

Again, this has the same relationship to what actaully goes according to the drawings of atoms you see in science books have to the real atoms.  It can help you to remember (for example) that an analytic function (n ° 8 in the list above) may rely on an aggregate function (#6), but not vice versa.

Yet once, SQL is not a procedural language, and the optimizer does not actually follow a rule of procedure like this.

Tags: Database

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