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Microsoft Word - mysql-set-operators.doc | Union
Union, Difference, Intersection, and Division in MySQL Instructor: Artem Chebotko. -- does not work; SELECT DISTINCT c1.y AS y FROM c c1 WHERE NOT EXISTS. (SELECT d.x FROM d LEFT OUTER JOIN c c2 USING (x) WHERE c2.y = c1.y AND c2.x IS NULL )

http://www.cs.kent.edu/~xlian/old_courses/CSCI4333_2014fall/MySQL-set-operators.pdf

064-29: Creating Efficient SQL - Union Join without the Union Clause
select aNumCol from a UNION select aCharCol from b. Alot more subtle and, worse yet, platform specific is the issue of database performance. Since each member of a UNION clause is itself a fully formed, stand alone fullselect statement, database implementations execute each member...

https://support.sas.com/resources/papers/proceedings/proceedings/sugi29/064-29.pdf

242-31: SQL Set Operators: So Handy Venn You Need Them
The UNION, INTERSECT, and EXCEPT operators by default purge duplicate rows (although the optional ALL keyword can be used to preempt this behavior). Because OUTER UNION results typically include mismatched columns, filled in with missing values, the very concept of duplicate rows is...

https://support.sas.com/resources/papers/proceedings/proceedings/sugi31/242-31.pdf

PowerPoint Presentation
from ds1 outer union corresponding select id. Terminology: A qseuteorypeornator cthoemFbRinOeMs tchlaeurseesuisltcsaollfetdwo oanr mino-lrineeqvuierwie.s. Check: obs with duplicate identifiers. select 'DS1' as DataSet,* from ds1 where id in (select id.

https://www.sas.com/content/dam/SAS/en_ca/User%20Group%20Presentations/TASS/bost_combine_data_sets.pdf

Nulls Make Things Easier?
SELECT NULL < NULL + 1; ?column? -(null). NULL represents unknown, not applicable, or unassigned. It has no data type, so comparing it to xed values always returns NULL. WITH ordertest AS ( SELECT NULL UNION ALL SELECT 2 UNION ALL SELECT 1 UNION ALL SELECT NULL.

https://momjian.us/main/writings/pgsql/nulls.pdf

Unlocking the Postgres Lock Manager
WHEN virtualxid IS NOT NULL AND transactionid IS NOT NULL THEN virtualxid || ’ ’ || transactionid WHEN virtualxid::text IS NOT NULL THEN virtualxid ELSE transactionid::text END AS xid_lock, relname, page, tuple, classid, objid, objsubid FROM pg_locks LEFT OUTER JOIN pg_class ON...

https://momjian.us/main/writings/pgsql/locking.pdf

Handling Missing Values in the SQL Procedure
IS [NOT] NULL and IS [NOT] MISSING predicates are two predicates especially designed to deal with missing values. IS [NOT] NULL is a SQL standard predicate and IS [NOT] MISSING is SAS SQL predicate. They are generic because they can handle both numeric and character variables.

https://stats.idre.ucla.edu/wp-content/uploads/2016/02/p004.pdf

COPY RIGHT -Final Trade Union Involvement in Skills Development
Trade unions are represented on the Board of the Flemish Agency for Vocational Training, and its Practical Committee, which are responsible for In France trade unions and employers’ associations have negotiated multi-sectoral collective agreements on skills development on a regular basis.

https://www.ilo.org/wcmsp5/groups/public/---ed_emp/---ifp_skills/documents/publication/wcms_585697.pdf

Union find
• Data: set of pairwise disjoint sets. • Required operations. – Union – merge two sets to create their union – Find – determine which set an item appears in. 3. Disjoint Sets and Naming.

https://courses.cs.washington.edu/courses/cse332/16sp/lectures/Lecture25/25_ho.pdf

Microsoft PowerPoint - 19-disjoint-union-find-part-2.ppt
CSE 326: Data Structures Disjoint Set Union/Find (part 2). Brian Curless Spring 2008. Decision Tree. Union: put one list on the end of the other, update set names of objects to be all the same.

https://courses.cs.washington.edu/courses/cse326/08sp/lectures/19-disjoint-union-find-part-2.pdf