Sql server ___________ (advance sql)

Session Objectives
 Explain the UNION, EXCEPT and
INTERSECT operators.
 Explain subqueries.
 Describe joins.
 Describe the various types of joins.

Introduction
 In large enterprises, there are huge
volumes of data stored in
databases.
 Data can be spread over several
tables that are related to one
another.
 When data is stored in such tables,
there must be some means to
combine and retrieve the data from
those tables.
 Using SQL Server, there are a
number of ways to combine data
from multiple tables.
Database
Table 1
Table 2
Table N
Table ..

Combining Data Using Operators
SQL Server provides certain keywords,
also called as operators, to combine data
from multiple tables. These operators are:
 UNION
 INTERSECT
 EXCEPT

UNION Operator - 1
 Combines results from two different query statements
into a single resultset.
Syntax:
Query_Statement1
UNION [ALL]
Query_Statement2
where,
Query_Statement1 and Query_Statement2 are SELECT statements.
UNION Operator:

Example of using UNION -1
Journals:
Books:
Consider that you want to see the title_id and title of all the books and
journals in an online library. To accomplish this, the records from both the
tables have to be retrieved. The data in the tables are as follows:

Records of Books table are displayed first, followed by those
in Journals table. This is because the records are sorted by
default on the basis of the first column. In this case, they are
sorted on title_id.
Example of using UNION -2

ALL clause of UNION Operator
By default, the UNION operator removes duplicate records from the resultset.
But, if you use the ALL clause with UNION operator, then all the rows are
returned.
Consider that you have an additional table named Publications with the
following data in the online library, and that the table has records as shown:

Example of ALL with UNION
The figure shows how to combine the data in the tables Books
and Publications using UNION with ALL. The query
displays all the records from both the tables.

INTERSECT Operator -1
The tables Publications and Books contain four records each:
Consider that you want to display only the rows that are common to both the
tables. To do this, you will need to use an operator named INTERSECT.

INTERSECT Operator -2
The INTERSECT operator is used with two query
statements to return a distinct set of rows that are
common to both the query statements.
Syntax:
Query_Statement1
INTERSECT
Query_Statement2
where,
Query_Statement1 and Query_Statement2 are SELECT statements.

Rules for using INTERSECT
The basic rules for using INTERSECT are:
 The number of columns and the order in which
they are given must be the same in both the
queries.
 The data types of the columns being used must be
compatible.

EXCEPT Operator
The two rules that apply to INTERSECT operator are also applicable for
EXCEPT operator.
Syntax:
Query_Statement1
EXCEPT
Query_Statement2
The EXCEPT operator returns all of the distinct
rows from the query given on the left of the
EXCEPT operator and removes all the rows
from the resultset that match the rows on the
right of the EXCEPT operator.

Subqueries
 You can use a SELECT statement or a query to return
records that will be used as criteria for another SELECT
statement or query. The outer query is called parent
query and the inner query is called a subquery.
 The simplest form of a subquery is one which returns
just one column. The parent query can use the results of
this subquery using an = sign.
SELECT <ColumnName> FROM <table>
WHERE <ColumnName> =
(
SELECT <ColumnName> FROM <Table> WHERE
<ColumnName> = <Condition>
)
Syntax:

Example of Subqueries
Consider that you want to know the names of titles from the
database pubs which are published by the publisher ‘New
Moon Books’.

ANY, ALL, IN, and EXISTS
 You can use a subquery instead of a value in
a WHERE clause of a SELECT statement.
 ANY, ALL, IN, and EXISTS are keywords that
can be used with the WHERE clause of a
SELECT statement when the query returns
one column but one or more rows.

EXISTS and NOT EXISTS
 The keyword EXISTS is used with a subquery to check the
existence of rows returned by the subquery. The subquery
does not actually return any data; it returns a value of
TRUE or FALSE.
SELECT <ColumnName> FROM <table>
WHERE [NOT] EXISTS
(
<Subquery_Statement>
)
Syntax:

Example of EXISTS
Consider that you want to determine if there
are any publishers who publish books in the
category of traditional cooking, that is,
‘trad_cook’. Here, you can use the
EXISTS keyword to check the existence of
any such books and then retrieve
information about their publishers. Example
1 shows the code for this.

Example 1
USE pubs
SELECT pub_id, pub_name, city
FROM publishers
WHERE EXISTS
(
SELECT pub_id FROM titles
WHERE pub_id = publishers.pub_id
AND type = ‘trad_cook’
)

Example of using NOT EXISTS
 Consider that you want to retrieve book details such as
name, type and published date for only those books that
are published by publishers other than ‘New Moon
Books’.
 The condition could be summarized as “publishers not
with pub_name New Moon Books”.
 This would result in the publisher information who are
other than ‘New Moon Books’.
 To perform this task, you need to use the NOT EXISTS
operator as shown in Example 2.

Example 2
USE pubs
GO
SELECT title, type, pubdate
FROM titles
WHERE NOT EXISTS
(
SELECT * FROM publishers
WHERE
pub_id = titles.pub_id
AND
pub_name = ’New Moon Books’
)

Sql server ___________ (advance sql)

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