Shulou(Shulou.com)06/01 Report--

(8) select (9) distinct (11)

(1) from

(3) join

(2) on

(4) where

(5) group by

(6) with {cube | rollup}

(7) having

(10) order by

The execution steps of the sql statement

1. Syntax analysis, analyze whether the syntax of the sentence conforms to the specification, and measure the meaning of each expression in the sentence.

two。 Semantic analysis to check whether all database objects involved in the statement exist, and the user has the corresponding permissions

3. View transformation, which converts the query statement involving the view into the corresponding query statement against the base table

4. Expression conversion, converting a complex sql expression to a simpler equivalent join expression

5. Choose an optimizer, and different optimizers generally produce different execution plans

6. Choose the link method. There are three connection methods, and the appropriate connection method can be selected for multi-table connection.

7. Select the join order, select which pair of tables to join first for the multi-table join, and select which of the two tables as the source data table

8. Select the search path of the data, and choose the appropriate data search path according to the above conditions, such as full table search, index or other methods.

9. Run the execution plan

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