WGU D191 Advanced Data Management Comprehensive Test
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Data Management
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 ...
, 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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