Mar 5, 2012 · Unique Key (UK): It's a column or a group of columns that can identify a uniqueness in a row. Primary Key (PK): It's also a column or group of columns that can identify a …

Apr 25, 2015 · Primary key can be related with another table's as a Foreign Key. We can generated ID automatically with the help of Auto Increment field. Primary key supports Auto …

Sep 25, 2010 · In complex tables, a unique key can be combinations of several columns and it will be inefficient to use unique key for identifying records for transactions. Hence primary key is …

Jul 5, 2010 · The above query will find all UNIQUE key constraints. However, it will not find PRIMARY KEY constraints, or UNIQUE indexes that were created outside a UNIQUE key …

So, basically, it means that every row returned in the result will be unique in terms of the combination of the select query columns. In OP's question, the below two result rows are …

Nov 7, 2009 · Unique key constraint is used to prevent the duplication of key values within the rows of a table and allow null values. (In oracle one null is not equal to another null). KEY or …

Primary keys are essentially combination of (unique +not null). also when referencing a foreign key the rdbms requires Primary key. Unique key just imposes uniqueness of the column.A …

Jul 5, 2011 · Here is the syntax for creating a unique CONSTRAINT as opposed to a unique INDEX. ALTER TABLE publishers ADD CONSTRAINT uqc_pub_name UNIQUE (pub_name) …

Jul 11, 2014 · I was making composite key of (ItemName,ItemSize) to uniquely identify item. And now after reading some answers on stackoverflow suggesting the use of UNIQUE i revised it …

Apr 21, 2016 · A primary key is the identifying column or set of columns of a table. Can be surrogate key or any other unique combination of columns (for example a compound key). …