hint提高sql语句的执行效率（Hint improves the execution efficiency of SQL statements）.doc

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hint提高sql语句的执行效率（Hint improves the execution efficiency of SQL statements）.doc

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hint提高sql语句的执行效率（Hint improves the execution efficiency of SQL statements）

hint提高sql语句的执行效率（Hint improves the execution efficiency of SQL statements） Using HINT to improve the execution efficiency of SQL statements Hints is a mechanism that Oracle provides to tell the optimizer to generate an execution plan in the way that we tell it. We can do it with hints: 1) the type of optimizer used 2) is the cost based optimizers optimization goal all_rows or first_rows?. 3) table access path is full table scan, or index scan, or direct use of ROWID?. 4) the connection type between tables 5) the connection order between tables 6) the degree of parallelism of statements 1, write the purpose of HINT Manually specifies the execution plan for the SQL statement Hints is a mechanism that Oracle provides to tell the optimizer to generate an execution plan in the way that we tell it. We can do it with hints: 1) the type of optimizer used 2) is the cost based optimizers optimization goal all_rows or first_rows?. 3) table access path is full table scan, or index scan, or direct use of ROWID?. 4) the connection type between tables 5) the connection order between tables 6) the degree of parallelism of statements 2, HINT can be based on the following rules Table connection order, table connection method, access path, parallelism 3, HINT application range DML statement Query statement 4, grammar + hint [text] [hint[text]]... Or -- hint [text] [hint[text]]... If the language is not correct, the ORACLE automatically ignores the written HINT and does not make a mistake 5, specifies the HINT of the optimizer mode RULE: regardless of whether statistics are available, rules based optimization will be used; CHOOSE: as long as a table in the accessed data has statistical information, it will be optimized in a cost based manner; FIRST_ROWS: regardless of whether statistics are available, the cost based approach will be optimized, with the goal of the fastest response time; ALL_ROWS: regardless of whether statistics are available, the cost based approach will be optimized,