Basically, a primary key is (at the implementation level) a special kind of index. Specifically: A table can have only one primary key, and with very few exceptions, every table should have one. A primary key is implicitly UNIQUE - you cannot have more than one row with the same primary key, since its purpose … See more A table can only have one primary key, but several indexes. A primary key is unique, whereas an index does not have to be unique. Therefore, the value of the primary … See more Each table should have a primary key. Define a primary key that is guaranteed to uniquely identify each record. If there are other columns you often use in joins or … See more None really - each one has its purpose. And it's not that you really can choose the one or the other. I recommend to always ask yourself first what the primary key of … See more WebAug 8, 2002 · There is no such thing as a "primary key index". A primary key is two things: o assures the values in a column(s) are unique o assures they are NOT NULL A primary key …
index on a primary key - Oracle Forums
WebJul 9, 2015 · create table structure and index. myworld->mystate->mycity->myhighschool. Example Our users enter how many females and males thay come in contact with on a given lecture. ,CONSTRAINT mystate_pk PRIMARY KEY (world_id, fiscalyear, state_id) insert into mystate select 100,'Ontario',1,2015 from dual; insert into mystate select … WebOracle Database does not index table rows in which all key columns are null, except for bitmap indexes or when the cluster key column value is null. Types of Indexes Oracle … bitsom faculty
sql - When should I use primary key or index? - Stack …
WebDec 9, 2010 · A primary key just happens to create a not null constraint and an index on the data (may be unique or non-unique index) in order to enforce itself -- but a not null … WebAug 5, 2024 · A primary key index is created by default when a table is created with a primary key specified. It will match the primary key in nature, in that it will be a single … WebOct 5, 2010 · I had gone through some documents provided in the timesten web-site, and i found that each Oracle table to be cached in TimesTen must have a primary key or a … bitsom college