Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.17) What are the Properties of Sub-Query? A sub query must be put in the right hand of the comparison operator, and A sub query cannot contain a ORDER-BY clause.
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User defined data types lets you extend the base SQL Server data types by providing a descriptive name, and format to the database.
For example, in your database, there is a column called Flight_Num which appears in many tables. In this case you could create a user defined data type called Flight_num_type of varchar(8) and use it across all your tables.
A database object in a relational database is a data structure used to either store or reference data.
The most common object that most people interact with is the table.
Relational Data Base Management Systems (RDBMS) that maintains data records and indices in tables.
Relationships may be created and maintained across and among the data and tables.2) What is SQL?
11) What is the difference among "dropping a table", "truncating a table" and "deleting all records" from a table?
Dropping: (Table structure Data are deleted), Invalidates the dependent objects, Drops the indexes Truncating: (Data alone deleted), Performs an automatic commit, Faster than delete Delete: (Data alone deleted), Doesn’t perform automatic commit Both primary key and unique enforce uniqueness of the column on which they are defined.
Note: OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.15) What is a self join?
Self join is just like any other join, except that two instances of the same table will be joined in the query.
What is being created is instances of the objects, such as a new table, an index on that table or a view on the same table.