CBO ? RBO? 很清晰的图示

最新推荐文章于 2023-06-08 16:32:35 发布

最新推荐文章于 2023-06-08 16:32:35 发布 · 109 阅读

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#Access

博客围绕数据库表访问展开，探讨了 ORDERED、FIRST_ROWS 等提示，还涉及 PARALLEL 设置、分区视图、索引组织表等情况。同时判断了 RULE 提示、SYSTEM 或 SESSION 级别的设置以及表的统计信息，以确定采用 COST 或 RULE 规则。

QUERY IN
|
|
\ /

-----------------------------------

| an object |

| or |

| Sample clauses |

| (Datawarehousing feature) |

| or |

| Parallel CTAS |

| or |

| Function-based indexes |

| or |

| Reverse Key Indexes |

| or |

| Query rewrite |

| (materialised views) |

| or |

| ANSI JOIN syntax is used |

| in the query |

-----------------------------------
|
| no
|
----------------------------------- yes
| Is there a RULE hint ? |-------> RULE
-----------------------------------

|
| no
|

-----------------------------------
| Is RULE set at SYSTEM or SESSION | yes
| level and no CHOOSE hint ? |-------> RULE
-----------------------------------
|
| no
|
-----------------------------------
| Is ALL_ROWS or FIRST_ROWS set at | yes
| SYSTEM or SESSION level and no |-------> COST
| CHOOSE hint ? |
-----------------------------------
|
| no
|
-----------------------------------
| Are there statistics for any of | yes
| the tables ? |-------> COST
-----------------------------------
|
| no
|
RULE