## Exercise #11 (tips and solutions) |
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The existence of the standard AVG aggregate function helps to fix all issues: However, the corresponding forum thread on the website shows the attempts to stand out from the "faceless mass. Here is quite a tantamount solution which, however, adds an extra operation to the query plan: The correctness of the following solution depends on the available restrictions: Namely, while SUM (speed) ignores rows with NULL values in the speed column, SUM(1) counts up all rows in the PC table and is essentially equivalent to COUNT(*). Hence, the numerator will contain the sum of speeds of all personal computers except for rows with unknown speed, which will be divided by the total number of rows. Therefore, the third solution will be equivalent to the other two only if no NULL values are allowed, i.e. a NOT NULL constraint is applied to the speed column. Return to discussion of exercise #11 |

aggregate functions
Airport
ALL
AND
AS keyword
ASCII
AVG
Battles
Bezhaev
Bismarck
C.J.Date
calculated columns
Cartesian product
CASE
cast
CHAR
CHARINDEX
Chebykin
check constraint
classes
COALESCE
common table expressions
comparison predicates
Computer firm
CONSTRAINT
CONVERT
correlated subqueries
COUNT
CROSS APPLY
CTE
data type conversion
data types
database schema
DATEADD
DATEDIFF
DATENAME
DATEPART
DATETIME
date_time functions
DDL
DEFAULT
DEFAULT VALUES
DELETE
DISTINCT
DML
duplicates
edge
equi-join
EXCEPT
exercise (-2)
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exercise 19
exercise 23
exercise 32
exercise 37
exercise 39
exercise 46
exercise 54
exercise 55
exercise 56
exercise 57
exercise 7
exercise 70
exercise 8
exercises
EXISTS
FLOAT
FOREIGN KEY
FROM
FULL JOIN
GROUP BY
grouping
Guadalcanal
HAVING
head ships
IDENTITY
IN
income
INFORMATION_SCHEMA
inner join
INSERT
INTERSECT
IS NOT NULL
IS NULL
ISNULL
join operations
laptop
launched year
LEFT
LEFT OUTER JOIN
LEN
LIKE
LTRIM
MAX
MIN
mistakes
money
MySQL
NATURAL JOIN
node
NOT
NOT IN
NULL
NULLIF
number sequences
number-sequence generation
numbering
ON DELETE CASCADE
OR
Oracle
ORDER BY
outcome
Outcomes
outer joins
OVER
paging
Painting
PARTITION BY
Pass_in_trip
PATINDEX
PC
PIVOT
PostgreSQL
predicates
primary key
printer
Product
Ranking functions
recursive CTE
renaming columns
REPLACE
RIGHT
RIGHT JOIN
ROUND
rounding
ROW_NUMBER
ships
sorting
SQL Server
SQL Server 2012
SQL-92
sql-ex.ru
string functions
subquery
SUBSTRING
SUM
tables join
tips and solutions
Torus
Transact-SQL
Trip
TRUNCATE TABLE
type conversion
UNION
UNION ALL
UNKNOWN
UNPIVOT
UPDATE
varchar
WHERE
window functions
WITH
XML
XPath
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