sql语句执行顺序SQL优化 - 图2

  1. (7) SELECT
  2. (8) DISTINCT <select_list>
  3. (1) FROM <left_table>
  4. (3) <join_type> JOIN <right_table>
  5. (2) ON <join_condition>
  6. (4) WHERE <where_condition>
  7. (5) GROUP BY <group_by_list>
  8. (6) HAVING <having_condition>
  9. (9) ORDER BY <order_by_condition>
  10. (10) LIMIT <limit_number>

PLSQL执行计划

执行顺序一般是：从右至左，从下至上
SQL优化 - 图3
技巧总结：1. 同一级若没有子ID就最先执行
2. 同一级执行遵循最上最后先执行的原则
INDEX RANGE SCAN —> TABLE ACCESS BY GLOBAL INDEX ROWID —> INDEX UNIQUE SCAN —> TABLE ACCESS BY INDEX ROWID —> NESTED LOOPS OUTER —> SORT GROUP BY —> SELECT STATEMENT, GOAL = ALL_ROWS