Sql server 2016 queries

SQL Server 2016 Queries
Seyed Ibrahim

Alias
• Column Alias
• When the column names are long
• More than one columns are to be combined
• SELECT FirstName As 'First Name', LastName AS 'Surname'
FROM StudentDetails;
• SELECT first_name FName FROM StudentDetails;
• Table Alias
• Common in Joins
• SELCT … FROM dbname.schemaname.tablename AS Aliasname

Operators
• Comparison Operators
• =
• <>, !=
• <
• >
• >=
• <=
• Logical Operators
• AND
• OR
• NOT

SQL Comparison Keywords
Comparison Operators Description
LIKE column value is similar to specified character(s).
IN column value is equal to any one of a specified values.
BETWEEN...AND column value is between two values, including the border values
IS NULL Check if the column is NULL

ROWCOUNT
This statement will limit the number of rows that will be
processed for the session in which the statement is executed
SET ROWCOUNT 3
SELECT * FROM ShareDetails.Shares
SET ROWCOUNT 0
SELECT * FROM ShareDetails.Shares

WHERE
• WHERE {column or expression} comparison-operator value
SELECT name, salary, salary*1.2 AS NewSalary
FROM dbo.employee
WHERE salary * 1.2 >= 80000 -- salary * 1.2 is an expression
SELECT name, salary, salary*1.2 AS NewSalary
FROM dbo.employee
WHERE salary < 80000 AND (grade BETWEEN 1 AND 5)

GROUP BY & HAVING
• GROUP BY: Groups a selected set of rows into a set of summary rows by the
values of one or more columns
SELECT dept_id, MIN(salary) AS LowestSalary
FROM dbo.employees
GROUP BY dept_id
• HAVING: Specifies a search condition for a group or an aggregate
SELECT SalesOrderID, SUM(LineTotal) AS SubTotal
FROM Sales.SalesOrderDetail
GROUP BY SalesOrderID
HAVING SUM(LineTotal) > 100000.00
ORDER BY SalesOrderID

ORDER BY
• There are no pointers, or Row numbers in RDBMS
• It is possible to change the order in which rows are returned
• ORDER BY clause can have multiple columns, with some in ascending order
and others in descending order
• ORDER BY Balance DESC
• ORDER BY name, salary
• ORDER BY 2,4

Subqueries
• a query embedded within another query or statement
SELECT *
FROM ShareDetails.Shares
WHERE ShareId IN (1,11,15)  Not a Subquery
• A Simple SubQuery using IN
SELECT id, first_name
FROM student_details
WHERE id IN (SELECT student_id
FROM student_subjects
WHERE subject= 'Science')

Correlated Subquery
• a sub-query that uses values from the outer query. In this case the inner query
has to be executed for every row of outer query
• May be inefficient
• E.g.: find all employees whose salary is above average for their department
SELECT employee_number, name
FROM employees AS emp
WHERE salary > (
SELECT AVG(salary)
FROM employees
WHERE department = emp.department);

What does this do?
SELECT orderid, custid
FROM Sales.Orders AS O1
WHERE orderid = (SELECT MAX(O2.orderid)
FROM Sales.Orders AS O2
WHERE O2.custid = O1.custid);
Exercise: Convert the above query to an efficient query

Sql server 2016 queries

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Sql server 2016 queries