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Exam (elaborations)

WGU D191 Advanced Data Management Comprehensive Test

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WGU D191 Advanced Data Management Comprehensive Test WGU D191 Advanced Data Management Comprehensive Test what is important about non-aggregate columns in reference to the GROUP BY clause? - ANSWER - non-aggregate fields must always be included in the GROUP BY clause; otherwise SQL interpreter ...

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  • September 15, 2024
  • 19
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers
  • Data management
  • Data management
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WGU D191 Advanced Data
Management Comprehensive
Test (2024) || Questions &
Answers (Graded A+)




CONCEPTIAL RESEARCHERS | conceptialresearch@gmail.com

, WGU D191 Advanced Data
Management Comprehensive Test
what is important about non-aggregate columns in reference to the GROUP BY
clause? - ANSWER - non-aggregate fields must always be included in the GROUP
BY clause; otherwise SQL interpreter will return an error (it will not know how to
group the results)

GROUPING SETS - ANSWER - SQL keyword that is a better alternative to UNION
ALL statements

syntax for GROUPING SETS - ANSWER - SELECT state, gender, COUNT(*) FROM
customers GROUP BY GROUPING SETS ((state), (gender), (state, gender))
ORDER BY 1, 2;

COPY command - ANSWER - PostgreSQL command that transfers data from a DB
to a file and vice versa

query planner - ANSWER - powerful SQL tool that analyzes a query request,
decides upon an execution path, but does not run; returns the results to the user;
helpful when analyzing overall execution times

syntax of a query planner (and breakdown of each section) - ANSWER - (1)
EXPLAIN (2) ANALYZE SELECT * FROM tablename WHERE clicked_date
BETWEEN '2011-01-01' AND '2011-02-01' (3) LIMIT 5;
(1) - command that will inform the interpreter to not execute the statement, but return
the query plan
(2) - collects stats about tables and indices and stores in internal tables
(3) - additional constraint that allows the planner to show two results - the results of a
LIMIT query aka the indicated tuples, the second the result of a full query unaffected
by the constraint

break down the result of a Query Plan:

Seq Scan on emails (cost = 0.00...9606.58 rows = 418158 width = 79)
(1 row) - ANSWER - Seq Scan = type of scan executed (standard sequential scan)
cost = First number is time expended before scan starts, second number is the total
cost in units of executing queries if all available rows are retrieved
rows = total number of rows that are available to be returned
width = width of each row in bytes
(1 row) = rows of the query plan returned

Cost Units in a query plan - ANSWER - unit that is used to reference how much a
query expends, specifically in the number of disk requests or page fetches

when is a hash index scan most effective? - ANSWER - For describing large data
sets using very little data

, syntax for creating an index using a specific scanning method - ANSWER - CREATE
INDEX indexname ON tablename(columnname) USING [HASH | BTREE]
(columnname);

While indexes make DB searching fundamentally faster, when is it not a effective to
use the index method? - ANSWER - - when the field you are using/DB is constantly
changing
- if the index is out of date
- when you are looking for records containing same search criteria w/in a specific
field (need to create partial index on subset of data)
- when the DB isn't that large (seq scan held in RAM are plenty fast enough)

syntax of creating a function in SQL (mul steps) - ANSWER - CREATE FUNCTION
function_name ([function_arguements])
RETURNS return_type AS $return_name$
[DECLARE return_name return_type;]

BEGIN
<function SQL statements>;

RETURN <some_value>;

END; $return_name$

LANGUAGE PLPGSQL;

stored procedure - ANSWER - special function in PostgreSQL that adds capabilities
to transaction computations; doesn't have a return value, rather IN or INOUT
parameters

syntax for a stored procedure - ANSWER - CREATE OR REPLACE PROCEDURE
procedure_name(IN parameter_name DATATYPE)
BEGIN
UPDATE tablename
SET <equation>
WHERE <condition>;

INSERT INTO tablename(column)
VALUES(TRUE, parameters);

COMMIT;

EXCEPTION WHEN OTHERS THEN
ROLLBACK;
END;
LANGUAGE plpgsql;

SQL trigger - ANSWER - execution of SQL statements or functions in response to a
specific event; also called "events" or "call backs"

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