So to summarise everything I understood from all the given answers, the difference between UNIQUE NOT NULL constraint and PRIMARY KEY constraint is: There can be AT MOST ONE attribute with Primary Key in the table. There can be AT LEAST ZERO attributes with Unique ...
Difference between Primary Key and Unique key 1. Behavior: Primary Key is used to identify a row (record) in a table, whereas Unique-key is to prevent duplicate values in a column (with the exception of a null entry). 2. Indexing: By default SQL-engine creates Clustered Index on primar...
1)Unique Key is nothing but it is uniqly identified each roe in Table.2)Unique Key Does not Allowes Duplicate values but allowes only one Null value.3)Primary key is default Non- Clustered indexes Regards, Narasima 0 Aug, 2008 22 The basic differences between Primary Key and U...
What is the basic difference between primary key and (unique key along with Not NULL). If we define a unique key as not null then it also take a unique value as well as not null value that means one can not insert Null value in that column. Thanks Was this answer useful? Yes Repl...
Angle between two lines Anti debugging code in C# any equivalent in c# for bytearray outputstream/inputstream and data outputstream/inputstream? App Config and escape sequences App Config key not working App setting inacessible due to protection level App.config for multiple groups of same key/...
For a load table, I think you are safe with either approach. The difference is when there are relationships created between tables. You would prefer, although not required, to create them using the primary keys. I'm curious. One of the supposed "best practices" is ...
Active directory configuration between Private and public network Active Directory could not resolve the following DNS host name of the source domain controller to an IP address. Active Directory Daily Check list ACTIVE DIRECTORY DCDIAG ERROR.. please someone help me to fix this. thanks and regards...
Is there any significant difference between ON UPDATE CASCADE and ON DELETE CASCADE My Parent Table CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ENGINE=INNODB; My Question is: What is the difference between the following sql queries. ON DELETE CASCADE CREATE TABLE child ...
As I said both primary and unique key uniquely identifies each row in the table but there is some subtle difference between them. here are some of them : 1.Unique keyin a tablecan benull, at least one but theprimary keycannot be nullin any table in a relational database like MySQL, ...
The SQL server is not left out of the picture as the compatible operating systems are Linux, Microsoft Server, and Microsoft Windows. Programming Language Support PostgreSQL There is a large difference between the programming languages that the PostgreSQL server supports and that of the SQL server....