Question

为什么Netezza没有“强制执行”外键约束，尽管它具有外键的概念？不执行约束的优点是什么？

Answer 1

查询优化器仍然使用

Foreign Keys来帮助构建最有效的查询计划，同时估算查询的成本。使用Foreign / Primary Keys来利用包括Microsoft Visio在内的许多数据库可视化工具也很重要。不强制执行约束的优点是速度。 Netezza能够通过不维护此功能来挤出额外的性能。

Netezza Manual

Answer 2

测试Netezza SQL：FOREIGN KEY子句

------------------------------------------------------------------
/*
NOTICE:  foreign key constraints not enforced       <-- Netezza SQL Parser complains here
 */
/* Start time 4/25/2013 6:21:32 PM, end time 4/25/2013 6:21:32 PM. */
/* Duration 0.078125 sec. */
CREATE TABLE table2ref
(
        col1    smallint NOT NULL
       ,colref2 smallint
       ,col3      varchar(30 )
  ,CONSTRAINT fk_column_colref2                                      <-- THIS IS REF CONSTRAINT
   FOREIGN KEY (colref2) 
   REFERENCES test2delete (col1)                     <-- the ref table must already be created 
);

/* Start time 4/25/2013 6:21:32 PM, end time 4/25/2013 6:21:37 PM. */
/* Duration 4.53125 sec. */                         <-- Observe how long the INSERT takes
/* Records Affected: 1. */

insert into table2ref values (3,12345,'reftabstring'); <-- THIS IS NON-EXISTING KEY "12345"

/* Start time 4/25/2013 6:21:37 PM, end time 4/25/2013 6:21:39 PM. */
/* Duration 2.65625 sec. */                         <-- Observe how long the INSERT takes
/* Records Affected: 1. */

insert into table2ref values (3,12345,'reftabstring');

Netezza外键约束

2 个答案: