SYNTACTIC_JOIN

强制执行联接顺序并启用其他联接提示。

语法

SELECT /*+SYN[TACTIC]_JOIN*/

描述

为了实现最佳性能，优化器经常覆盖查询的指定联接顺序。通过包括 SYNTACTIC_JOIN 提示，可以确保优化器严格按规定强制执行查询的联接顺序。一个要求适用：联接语法必须符合 ANSI SQL-92 惯例。

SYNTACTIC_JOIN 提示必须紧跟在 SELECT 后面。如果带注释查询包含的另一个提示也必须跟在 SELECT 后面（例如 VERBATIM），则将这两个提示组合在一起。例如：

SELECT /*+ syntactic_join,verbatim*/

示例

在以下示例中，优化器为两个查询产生不同的计划，区别就在于包括或排除了 SYNTACTIC_JOIN 提示。

排除 SYNTACTIC_JOIN

EXPLAIN SELECT sales.store_key, stores.store_name, products.product_description, sales.sales_quantity, sales.sale_date
FROM (store.store_sales sales JOIN products ON sales.product_key=products.product_key)
JOIN store.store_dimension stores ON sales.store_key=stores.store_key
WHERE sales.sale_date='2014-12-01' order by sales.store_key, sales.sale_date;

 Access Path:
 +-SORT [Cost: 14K, Rows: 100K (NO STATISTICS)] (PATH ID: 1)
 |  Order: sales.store_key ASC, sales.sale_date ASC
 |  Execute on: All Nodes
 | +---> JOIN HASH [Cost: 11K, Rows: 100K (NO STATISTICS)] (PATH ID: 2) Outer (RESEGMENT)(LOCAL ROUND ROBIN) Inner (RESEGMENT)
 | |      Join Cond: (sales.product_key = products.product_key)
 | |      Materialize at Input: sales.store_key, sales.product_key, sales.sale_date, sales.sales_quantity
 | |      Execute on: All Nodes
 | | +-- Outer -> JOIN HASH [Cost: 1K, Rows: 100K (NO STATISTICS)] (PATH ID: 3)
 | | |      Join Cond: (sales.store_key = stores.store_key)
 | | |      Execute on: All Nodes
 | | | +-- Outer -> STORAGE ACCESS for sales [Cost: 1K, Rows: 100K (NO STATISTICS)] (PATH ID: 4)
 | | | |      Projection: store.store_sales_b0
 | | | |      Materialize: sales.store_key
 | | | |      Filter: (sales.sale_date = '2014-12-01'::date)
 | | | |      Execute on: All Nodes
 | | | |      Runtime Filter: (SIP1(HashJoin): sales.store_key)
 | | | +-- Inner -> STORAGE ACCESS for stores [Cost: 34, Rows: 250] (PATH ID: 5)
 | | | |      Projection: store.store_dimension_DBD_10_rep_VMartDesign_node0001
 | | | |      Materialize: stores.store_key, stores.store_name
 | | | |      Execute on: All Nodes
 | | +-- Inner -> STORAGE ACCESS for products [Cost: 3K, Rows: 60K (NO STATISTICS)] (PATH ID: 6)
 | | |      Projection: public.products_b0
 | | |      Materialize: products.product_key, products.product_description
 | | |      Execute on: All Nodes

包括 SYNTACTIC_JOIN

EXPLAIN SELECT /*+SYNTACTIC_JOIN*/ sales.store_key, stores.store_name, products.product_description, sales.sales_quantity, sales.sale_date
FROM (store.store_sales sales JOIN products ON sales.product_key=products.product_key)
JOIN store.store_dimension stores ON sales.store_key=stores.store_key
WHERE sales.sale_date='2014-12-01' order by sales.store_key, sales.sale_date;

 Access Path:
 +-SORT [Cost: 11K, Rows: 100K (NO STATISTICS)] (PATH ID: 1)
 |  Order: sales.store_key ASC, sales.sale_date ASC
 |  Execute on: All Nodes
 | +---> JOIN HASH [Cost: 8K, Rows: 100K (NO STATISTICS)] (PATH ID: 2)
 | |      Join Cond: (sales.store_key = stores.store_key)
 | |      Execute on: All Nodes
 | | +-- Outer -> JOIN HASH [Cost: 7K, Rows: 100K (NO STATISTICS)] (PATH ID: 3) Outer (BROADCAST)(LOCAL ROUND ROBIN)
 | | |      Join Cond: (sales.product_key = products.product_key)
 | | |      Execute on: All Nodes
 | | |      Runtime Filter: (SIP1(HashJoin): sales.store_key)
 | | | +-- Outer -> STORAGE ACCESS for sales [Cost: 2K, Rows: 100K (NO STATISTICS)] (PATH ID: 4)
 | | | |      Projection: store.store_sales_b0
 | | | |      Materialize: sales.sale_date, sales.store_key, sales.product_key, sales.sales_quantity
 | | | |      Filter: (sales.sale_date = '2014-12-01'::date)
 | | | |      Execute on: All Nodes
 | | | +-- Inner -> STORAGE ACCESS for products [Cost: 3K, Rows: 60K (NO STATISTICS)] (PATH ID: 5)
 | | | |      Projection: public.products_b0
 | | | |      Materialize: products.product_key, products.product_description
 | | | |      Execute on: All Nodes
 | | +-- Inner -> STORAGE ACCESS for stores [Cost: 34, Rows: 250] (PATH ID: 6)
 | | |      Projection: store.store_dimension_DBD_10_rep_VMartDesign_node0001
 | | |      Materialize: stores.store_key, stores.store_name
 | | |      Execute on: All Nodes