primary index 和secondary indexPrimary Index是指数据库表中的主索引,Secondary Index是指数据库表中的次要索引。 Primary Index在数据库表中是唯一的,不允许有空值。Secondary Index在数据库表中不是唯一的,允许有空值。©2022 Baidu |由 百度智能云 提供计算服务 | 使用百度前必读 | 文库协议 | 网站地图 | 百度营销
+ and it must be unique!, if all key fields are use with equal, they specify exactly one record The uniquiness is necessary for a DIRECT read, the primary key MUST be unique, the secondary index can be unique. The used index is determined by the optimizer with the fields given in th...
A wire device receives: configuration parameters of: a primary cell with a primary physical uplink control channel (PUCCH); and a secondary cell with a secondary PUCCH; a transmit power control (TPC) radio network temporary identifier (RNTI); a primary TPC index of the primary PUCCH; and a...
CREATE index tidx on t (n, pid) include (id); ERROR: index "tidx" already contains column "id" SQLSTATE: 42701 DETAIL: column "id" is part of the primary index and therefore implicit in all indexes Instead of error we should no-op this and just show a warning: CREATE index tidx...
Bug #56714 Slow MAX() on primary key retrieved by secondary index in InnoDB Submitted: 10 Sep 2010 12:45Modified: 2 Apr 2013 7:20 Reporter: Nicholas Sherlock Email Updates: Status: Closed Impact on me: None Category: MySQL Server: OptimizerSeverity: S5 (Performance) Version: 5.1.50, ...
(1,NULL). Now, let us assume that you ask for this optimization only when the unique index does not allow NULL values. Another problematic and maybe improbable case would be the update of the PRIMARY KEY. Let us assume the following: CREATE TABLE t2 (a INT, b INT, c INT, d INT ...
Can you have a primary and secondayr sort field when you view an Access table or can you only sort one field at a time? Sort by date Sort by votes Jun 26, 2009 1 #2 PHV MIS Nov 8, 2002 53,708 FR You may create composite index. Hope This Helps, PH. FAQ219-2884 FAQ181...
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Size is key to performance. If you have a PK on a char(10) and its clustered then its 2.5 times larger than using an integer. And all your other indexes are based on it and thus a knock on affect. Using composite keys results in multi column joins, increased index size, an...
The NAV documentation clearly indicates that a primary key is limited to 20 fields and that the number of fields in the primary key together with all the fields in secondary key must not exceed 20. Furthermore, it states that a SumIndexField can have at most 20 SumIn...