Announcements. Joins in SQL. Joins in SQL. (Inner) joins. Joins in SQL. Introduction to Database Systems CSE 414

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1 Announcements Introduction to Database Sstems CSE 414 Lecture 4: SQL Joins and Aggregates WQ1 due on Tuesda No late das allowed HW1 due on Tuesda Submit using script in repo WQ2 and HW2 will be out tomorrow Both are 1 week assignments Check website for up to date OHs 1 2 (p, price, categor, manufacturer) (, ) (p, price, categor, manufacturer) (, ) Joins in SQL Joins in SQL p price categor manufacturer MultiTouch SingleTouch photograph Giom 50 Works Super Works Works p price categor manufacturer MultiTouch SingleTouch photograph Giom 50 Works Super Works Works Retrieve all ese products that cost < $150 SELECT P.p, P.price Join Predicate FROM as P, as C WHERE P.manufacturer=C. AND C.='' AND C.price < Selection predicates Retrieve all companies that manufacture products 4 (p, price, categor, manufacturer) (, ) Joins in SQL p price categor manufacturer MultiTouch SingleTouch photograph Giom 50 Works Super Works Works Retrieve all companies that manufacture products Wh SELECT DISTINCT C. DISTINCT? FROM as P, as C WHERE C.='' AND P.categor = '' AND P.manufacturer = 5 (p, price, categor, manufacturer) (, ) -- manufacturer is foreign ke to SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = 6 1

2 SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = Works Works Works Works 7 8 SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = Works Works Works Works 9 Works Works 10 SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = Works Works Works Works

3 SELECT DISTINCT FROM, WHERE ='' AND categor = '' AND manufacturer = (Inner) Joins SELECT 1.a1, 2.a2, m.am FROM R1 as 1, R2 as 2, Rm as m WHERE Cond SELECT DISTINCT FROM JOIN ON = '' AND categor = '' AND manufacturer = 13 for 1 in R1: for 2 in R2:... for m in Rm: if Cond(1, 2 ): output(1.a1, 2.a2, m.am) This is called nested loop semantics since we are 14 interpreting what a join means using a nested loop Another eample (p, price, categor, manufacturer) (, ) -- manufacturer is foreign ke to s and photo products Another eample (p, price, categor, manufacturer) (, ) -- manufacturer is foreign ke to s and photo products SELECT DISTINCT. FROM, WHERE. = AND.manufacturer =. AND.categor = ' AND.categor = 'photograph; Does this work? Another eample (p, price, categor, manufacturer) (, ) -- manufacturer is foreign ke to s and photo products SELECT DISTINCT. FROM, WHERE. = AND.manufacturer =. AND (.categor = ' OR.categor = 'photograph); What about this? 17 Another eample (p, price, categor, manufacturer) (, ) -- manufacturer is foreign ke to s and photo products SELECT DISTINCT. FROM,, WHERE. = AND.manufacturer =. Need to include AND.manufacturer =. twice! AND.categor = ' AND.categor CSE = 'photograph; Spring

4 Self-Joins and Tuple Variables s and photo products Joining with is insufficient: need to join, with, and with When a relation occurs twice in the FROM clause we call it a self-join; in that case we must use tuple variables (aka table aliases) (wh?) SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works SingleTouch photo MultiTouch Works Works SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works Works Works Works SingleTouch photo SingleTouch photo MultiTouch Works MultiTouch Works SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works Works Works Works SingleTouch photo SingleTouch photo MultiTouch Works MultiTouch Works

5 SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works SingleTouch photo Works Works SingleTouch photo Works MultiTouch Works MultiTouch Works SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works Works Works Works SingleTouch photo MultiTouch Works SingleTouch photo MultiTouch Works.p.categor.manufacturer.p.categor.manufacturer.. 27 Works MultiTouch Works Works SELECT DISTINCT. FROM,, WHERE. = AND.categor = AND.manufacturer =. AND.manufacturer =.; Works SingleTouch photo MultiTouch Works Works Joins in SQL The join we have just seen is sometimes called an inner join Each row in the result must come from both tables in the join Sometimes we want to include rows from onl one of the two table: outer join.p.categor.manufacturer.p.categor.manufacturer.. Works MultiTouch Works Works 31 5

6 Emploee(, ) (emploeeid, ) Emploee emploeeid Retrieve emploees and their sales Emploee(, ) (emploeeid, ) Emploee emploeeid Retrieve emploees and their sales FROM Emploee E, S WHERE E. = S.emploeeID Emploee(, ) (emploeeid, ) Emploee emploeeid Emploee(, ) (emploeeid, ) Emploee emploeeid Retrieve emploees and their sales Retrieve emploees and their sales Jill is missing empoleeid FROM Emploee E, S WHERE E. = S.emploeeID 34 empoleeid FROM Emploee E, S WHERE E. = S.emploeeID 35 Emploee(, ) (emploeeid, ) Emploee emploeeid Retrieve emploees and their sales FROM Alternative snta Emploee E INNER JOIN S ON E. = S.emploeeID Jill is missing empoleeid 36 Emploee(, ) (emploeeid, ) Emploee Outer Join emploeeid Retrieve emploees and their sales FROM Emploee E LEFT OUTER JOIN S ON E. = S.emploeeID Jill is present empoleeid NULL NULL 6

7 Outer joins (, categor) (prod, store) SELECT.,.store FROM JOIN ON. =.prod Prod -- prod is foreign ke SELECT.,.store FROM LEFT OUTER JOIN ON. =.prod SELECT.,.store FROM JOIN ON. =.prod SELECT.,.store FROM JOIN ON. =.prod Prod Prod SELECT.,.store FROM JOIN ON. =.prod SELECT.,.store FROM JOIN ON. =.prod Prod Prod

8 SELECT.,.store FROM JOIN ON. =.prod SELECT.,.store FROM JOIN ON. =.prod Prod Prod SELECT.,.store FROM JOIN ON. =.prod SELECT.,.store FROM JOIN ON. =.prod Prod Prod SELECT.,.store FROM LEFT OUTER JOIN ON. =.prod SELECT.,.store FROM LEFT OUTER JOIN ON. =.prod Prod Prod NULL

9 SELECT.,.store FROM FULL OUTER JOIN ON. =.prod Prod Phone Foo NULL NULL Foo 50 Outer Joins tablea (LEFT/RIGHT/FULL) OUTER JOIN tableb ON p Left outer join: Include tuples from tablea even if no match Right outer join: Include tuples from tableb even if no match Full outer join: Include tuples from both even if no match In all cases: Patch tuples without matches using NULL 51 9