What is Cursor?
Cursor is a database
object used by applications to manipulate data in a set on a row-by-row basis,
instead of the typical SQL commands that operate on all the rows in the set at
one time.
In order to work with
a cursor we need to perform some steps in the following order:
- Declare cursor
- Open cursor
- Fetch row from the cursor
- Process fetched row
- Close cursor
- Deal-locate cursor
What is Collation
Collation refers to a set of rules that determine how data is
sorted and compared. Character data is sorted using rules that define the
correct character sequence, with options for specifying case sensitivity,
accent marks, kana character types and character width.
What is Difference between Function and Stored Procedure?
UDF can be used in the
SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored
procedures cannot be. UDFs that return tables can be treated as another rowset.
This can be used in JOINs with other tables. Inline UDF’s can be thought of as
views that take parameters and can be used in JOINs and other Rowset
operations.
What is sub-query? Explain properties of sub-query?
Sub-queries are often
referred to as sub-selects, as they allow a SELECT statement to be executed
arbitrarily within the body of another SQL statement. A sub-query is executed
by enclosing it in a set of parentheses. Sub-queries are generally used to return
a single row as an atomic value, though they may be used to compare values
against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another
T-SQL statement. A subquery SELECT statement if executed independently of the
T-SQL statement, in which it is nested, will return a resultset. Meaning a
subquery SELECT statement can standalone and is not depended on the statement
in which it is nested. A subquery SELECT statement can return any number of
values, and can be found in, the column list of a SELECT statement, a FROM,
GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can
also be used as a parameter to a function call. Basically a subquery can be
used anywhere an expression can be used.
What are different Types of Join?
Cross Join
A cross join that does
not have a WHERE clause produces the Cartesian product of the tables involved
in the join. The size of a Cartesian product result set is the number of rows
in the first table multiplied by the number of rows in the second table. The
common example is when company wants to combine each product with a pricing
table to analyze each product at each price.
Inner Join
A join that displays
only the rows that have a match in both joined tables is known as inner
Join. This is the default type of join in the Query and View Designer.
Outer Join
A join that includes
rows even if they do not have related rows in the joined table is an Outer
Join. You can create three different outer join to specify the unmatched
rows to be included:
- Left Outer Join: In Left Outer Join all rows in the first-named table i.e. “left” table, which appears leftmost in the JOIN clause are included. Unmatched rows in the right table do not appear.
- Right Outer Join: In Right Outer Join all rows in the second-named table i.e. “right” table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
- Full Outer Join: In Full Outer Join all rows in all joined tables are included, whether they are matched or not.
Self Join
This is a particular case when one table joins to itself, with
one or two aliases to avoid confusion. A self join can be of any type, as long
as the joined tables are the same. A self join is rather unique in that it involves
a relationship with only one table. The common example is when company has a hierarchical reporting structure whereby one member of staff reports to another.
Self Join can be Outer Join or Inner Join.
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