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CSE544: SQL
Monday 3/27 and Wednesday 3/29, 2006
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SQL
Data Definition Language (DDL)
Create/alter/delete tables and their attributes
Following lectures...
Data Manipulation Language (DML)
Query one or more tablesdiscussed next !
Insert/delete/modify tuples in tables
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Tables in SQL
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography Canon
MultiTouch $203.99 Household Hitachi
Product
Attribute namesTable name
Tuples or rows
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Data Types in SQL
Atomic types:
Characters: CHAR(20), VARCHAR(50)
Numbers: INT, BIGINT, SMALLINT, FLOAT Others: MONEY, DATETIME,
Every attribute must have an atomic typeHence tables are flatWhy ?
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Tables Explained
A tuple = a record
Restriction: all attributes are of atomic type
A table = a set of tuples
Like a list
but it is unorderd:
no first(), no next(), no last().
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SQL Query
Basic form: (plus many many more bells and whistles)
SELECT
FROM
WHERE
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Simple SQL Query
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography CanonMultiTouch $203.99 Household Hitachi
SELECT *
FROM Product
WHERE category=Gadgets
Product
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorksselection
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Simple SQL Query
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography CanonMultiTouch $203.99 Household Hitachi
SELECT PName, Price, Manufacturer
FROM Product
WHERE Price > 100
Product
PName Price Manufacturer
SingleTouch $149.99 Canon
MultiTouch $203.99 Hitachi
selection and
projection
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Notation
Product(PName, Price, Category, Manfacturer)
Answer(PName, Price, Manfacturer)
Input Schema
Output Schema
SELECT PName, Price, Manufacturer
FROM Product
WHERE Price > 100
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Details
Case insensitive:
Same: SELECT Select select
Same: Product product Different: Seattle seattle
Constants: abc - yes
abc - no
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The LIKEoperator
s LIKEp: pattern matching on strings
p may contain two special symbols:
% = any sequence of characters
_ = any single character
SELECT *FROM ProductsWHERE PName LIKE%gizmo%
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Eliminating Duplicates
SELECT DISTINCTcategory
FROM Product
Compare to:
SELECT category
FROM Product
Category
Gadgets
Gadgets
Photography
Household
Category
Gadgets
Photography
Household
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Ordering the Results
SELECT pname, price, manufacturer
FROM Product
WHERE category=gizmo AND price > 50ORDER BY price, pname
Ties are broken by the second attribute on the ORDER BY list, etc.
Ordering is ascending, unless you specify the DESC keyword.
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SELECT Category
FROM Product
ORDER BY PName
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography Canon
MultiTouch $203.99 Household Hitachi
?
SELECT DISTINCTcategory
FROM Product
ORDER BYcategory
SELECT DISTINCTcategory
FROM Product
ORDER BYPName
?
?
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Keys and Foreign Keys
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography Canon
MultiTouch $203.99 Household Hitachi
Product
Company
CName StockPrice Country
GizmoWorks 25 USA
Canon 65 Japan
Hitachi 15 Japan
Key
Foreign
key
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Joins
Product (pname, price, category, manufacturer)
Company (cname, stockPrice, country)
Find all products under $200 manufactured in Japan;return their names and prices.
SELECT PName, Price
FROM Product, CompanyWHERE Manufacturer=CName AND Country=Japan
AND Price
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Joins
PName Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography Canon
MultiTouch $203.99 Household Hitachi
ProductCompany
Cname StockPrice Country
GizmoWorks 25 USA
Canon 65 Japan
Hitachi 15 Japan
PName Price
SingleTouch $149.99
SELECT PName, Price
FROM Product, CompanyWHERE Manufacturer=CName AND Country=Japan
AND Price
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More Joins
Product (pname, price, category, manufacturer)
Company (cname, stockPrice, country)
Find all Chinese companies that manufacture productsboth in the electronic and toy categories
SELECT cname
FROM
WHERE
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A Subtlety about Joins
Product (pname, price, category, manufacturer)
Company (cname, stockPrice, country)
Find all countries that manufacture some product in theGadgets category.
SELECT Country
FROM Product, CompanyWHERE Manufacturer=CName AND Category=Gadgets
Unexpected duplicates
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A Subtlety about Joins
Name Price Category Manufacturer
Gizmo $19.99 Gadgets GizmoWorks
Powergizmo $29.99 Gadgets GizmoWorks
SingleTouch $149.99 Photography Canon
MultiTouch $203.99 Household Hitachi
ProductCompany
Cname StockPrice Country
GizmoWorks 25 USA
Canon 65 Japan
Hitachi 15 Japan
Country
??
??
What isthe problem ?
Whats the
solution ?
SELECT Country
FROM Product, Company
WHERE Manufacturer=CName AND Category=Gadgets
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Tuple Variables
SELECT DISTINCTpname, address
FROM Person, Company
WHERE worksfor = cname
Which
address ?
Person(pname, address, worksfor)
Company(cname, address)
SELECT DISTINCTPerson.pname, Company.address
FROM Person, CompanyWHERE Person.worksfor = Company.cname
SELECT DISTINCTx.pname, y.address
FROM Person AS x, Company AS y
WHERE x.worksfor = y.cname
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Meaning (Semantics) of SQL
QueriesSELECTa1, a2, , akFROM R1AS x1, R2AS x2, , RnAS xnWHERE Conditions
Answer = {}forx1inR1do
forx2inR2do
..forxninRndoifConditions
thenAnswer = Answer {(a1,,ak)}returnAnswer
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SELECT DISTINCTR.A
FROM R, S, TWHERE R.A=S.A OR R.A=T.A
An Unintuitive Query
Computes R (S T) But what if S = f?
What does it compute ?
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Subqueries Returning Relations
SELECT Company.city
FROM Company
WHERE Company.name IN(SELECTProduct.maker
FROM Purchase , Product
WHEREProduct.pname=Purchase.product
AND Purchase .buyer = Joe Blow);
Return cities where one can find companies that manufactureproducts bought by Joe Blow
Company(name, city)
Product(pname, maker)
Purchase(id, product, buyer)
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Subqueries Returning Relations
SELECT Company.cityFROM Company, Product, Purchase
WHERE Company.name= Product.maker
AND Product.pname = Purchase.product
AND Purchase.buyer = Joe Blow
Is it equivalent to this ?
Beware of duplicates !
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Removing Duplicates
Now
they are
equivalent
SELECTDISTINCTCompany.city
FROM Company
WHERE Company.name IN
(SELECTProduct.maker
FROM Purchase , Product
WHEREProduct.pname=Purchase.product
AND Purchase .buyer = Joe Blow);
SELECTDISTINCTCompany.cityFROM Company, Product, Purchase
WHERE Company.name= Product.maker
AND Product.pname = Purchase.product
AND Purchase.buyer = Joe Blow
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Subqueries Returning Relations
SELECT nameFROM Product
WHERE price > ALL(SELECTprice
FROM Purchase
WHERE maker=Gizmo-Works)
Product ( pname, price, category, maker)Find products that are more expensive than all those produced
By Gizmo-Works
You can also use: s > ALL R
s > ANY R
EXISTS R
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Question for Database Fans
and their Friends Can we express this query as a single
SELECT-FROM-WHERE query, without
subqueries ?
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Question for Database Fans
and their Friends Answer: all SFW queries are
monotone(figure out what this means).
A query with ALLis not monotone
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Correlated Queries
SELECTDISTINCTtitle
FROM Movie AS x
WHERE year ANY
(SELECT year
FROM MovieWHERE title = x.title);
Movie (title, year, director, length)
Find movies whose title appears more than once.
Note (1) scope of variables (2) this can still be expressed as single SFW
correlation
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Complex Correlated Query
Product ( pname, price, category, maker, year)
Find products (and their manufacturers) that are more expensivethan all products made by the same manufacturer before 1972
Very powerful ! Also much harder to optimize.
SELECT DISTINCT pname, makerFROM Product AS xWHERE price > ALL (SELECT price
FROM Product AS y
WHERE x.maker = y.maker AND y.year < 1972);
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Aggregation
SELECT count(*)
FROM Product
WHERE year > 1995
Except count, all aggregations apply to a single attribute
SELECT avg(price)
FROM Product
WHERE maker=Toyota
SQL supports several aggregation operations:
sum, count, min, max, avg
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COUNT applies to duplicates, unless otherwise stated:
SELECT Count(category)
FROM Product
WHERE year > 1995
same as Count(*)
We probably want:
SELECT Count(DISTINCTcategory)
FROM Product
WHERE year > 1995
Aggregation: Count
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Purchase(product, date, price, quantity)
More Examples
SELECT Sum(price * quantity)
FROM Purchase
SELECT Sum(price * quantity)
FROM Purchase
WHERE product = bagel
What do
they mean ?
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Simple AggregationsPurchase
Product Date Price Quantity
Bagel 10/21 1 20
Banana 10/3 0.5 10
Banana 10/10 1 10
Bagel 10/25 1.50 20
SELECT Sum(price * quantity)
FROM Purchase
WHERE product = bagel50 (= 20+30)
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Grouping and AggregationPurchase(product, date, price, quantity)
SELECT product, Sum(price*quantity) AS TotalSales
FROM Purchase
WHERE date > 10/1/2005
GROUP BY product
Lets see what this means
Find total sales after 10/1/2005 per product.
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Grouping and Aggregation
1. Compute the FROMand WHEREclauses.
2. Group by the attributes in the GROUPBY
3. Compute the SELECTclause: grouped attributes and aggregates.
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1&2. FROM-WHERE-GROUPBY
Product Date Price Quantity
Bagel 10/21 1 20
Bagel 10/25 1.50 20
Banana 10/3 0.5 10
Banana 10/10 1 10
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3. SELECT
SELECT product, Sum(price*quantity) AS TotalSalesFROM Purchase
WHERE date > 10/1/2005
GROUP BY product
Product Date Price Quantity
Bagel 10/21 1 20
Bagel 10/25 1.50 20
Banana 10/3 0.5 10Banana 10/10 1 10
Product TotalSales
Bagel 50
Banana 15
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GROUP BY v.s. Nested Quereis
SELECT product, Sum(price*quantity) ASTotalSalesFROM Purchase
WHERE date > 10/1/2005
GROUP BY product
SELECT DISTINCT x.product, (SELECTSum(y.price*y.quantity)
FROM Purchase y
WHEREx.product = y.product
AND y.date > 10/1/2005)ASTotalSales
FROM Purchase x
WHERE x.date > 10/1/2005
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Another Example
SELECT product,sum(price * quantity) AS SumSales
max(quantity) AS MaxQuantity
FROM Purchase
GROUP BYproduct
What does
it mean ?
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HAVING Clause
SELECT product, Sum(price * quantity)
FROM Purchase
WHERE date > 10/1/2005
GROUPBYproduct
HAVING Sum(quantity) > 30
Same query, except that we consider only products that had
at least 100 buyers.
HAVING clause contains conditions on aggregates.
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General form of Grouping and
AggregationSELECT S
FROM R1,,Rn
WHERE C1GROUP BYa1,,akHAVING C2
S = may contain attributes a1,,akand/or any aggregates but NO OTHERATTRIBUTES
C1 = is any condition on the attributes in R1,,RnC2 = is any condition on aggregate expressions
Why ?
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General form of Grouping and
Aggregation
Evaluation steps:
1. Evaluate FROM-WHERE, apply condition C12. Group by the attributes a1,,ak
3. Apply condition C2 to each group (may have aggregates)
4. Compute aggregates in S and return the result
SELECT S
FROM R1,,RnWHERE C1
GROUP BYa1,,akHAVING C2
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Advanced SQLizing
1. Getting around INTERSECT and EXCEPT
2. Quantifiers
3. Aggregation v.s. subqueries
INTERSECT and EXCEPT: not in SQL Server
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1. INTERSECT and EXCEPT:
(SELECTR.A, R.BFROM R)
INTERSECT
(SELECTS.A, S.BFROM S)
SELECTR.A, R.BFROM RWHERE
EXISTS(SELECT*FROMSWHERER.A=S.A and R.B=S.B)
(SELECTR.A, R.B
FROM R)EXCEPT
(SELECTS.A, S.BFROM S)
SELECTR.A, R.B
FROM RWHERENOT EXISTS(SELECT*
FROMSWHERER.A=S.A and R.B=S.B)
If R, S have no
duplicates, then can
write without
subqueries
(HOW ?)
INTERSECT and EXCEPT: not in SQL Server
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2. Quantifiers
Product ( pname, price, company)
Company( cname, city)
Find all companies that make some products with price < 100
SELECT DISTINCT Company.cnameFROM Company, ProductWHERE Company.cname = Product.company and Product.price < 100
Existential: easy !
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2. Quantifiers
Product ( pname, price, company)
Company( cname, city)
Find all companies s.t. all of their products have price < 100
Universal: hard !
Find all companies that make only products with price < 100
same as:
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2. Quantifiers
2. Find all companies s.t. all their products have price < 100
1. Find the other companies: i.e. s.t. some product 100
SELECT DISTINCT Company.cnameFROM CompanyWHERE Company.cname IN(SELECTProduct.company
FROMProductWHEREProduc.price >= 100
SELECT DISTINCT Company.cnameFROM CompanyWHERE Company.cnameNOTIN(SELECTProduct.company
FROMProductWHEREProduc.price >= 100
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3. Group-by v.s. Nested Query
Find authors who wrote 10 documents:
Attempt 1: with nested queries
SELECTDISTINCTAuthor.name
FROM Author
WHERE count(SELECTWrote.urlFROMWrote
WHEREAuthor.login=Wrote.login)
> 10
This isSQL by
a novice
Author(login,name)Wrote(login,url)
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3. Group-by v.s. Nested Query
Find all authors who wrote at least 10
documents:
Attempt 2: SQL style (with GROUP BY)
SELECT Author.name
FROM Author, Wrote
WHERE Author.login=Wrote.loginGROUP BYAuthor.name
HAVING count(wrote.url) > 10
This is
SQL by
an expert
No need for DISTINCT: automatically from GROUP BY
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3. Group-by v.s. Nested Query
Find authors with vocabulary 10000 words:
SELECT Author.name
FROM Author, Wrote, MentionsWHERE Author.login=Wrote.login AND Wrote.url=Mentions.url
GROUP BY Author.name
HAVING count(distinct Mentions.word) > 10000
Author(login,name)
Wrote(login,url)
Mentions(url,word)
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Two Examples
Store(sid, sname)
Product(pid, pname, price, sid)
Find all stores that sell onlyproducts with price > 100
same as:
Find all stores s.t. all their products have price > 100)
SELECT Store.name
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SELECTStore.name
FROM Store, Product
WHERE Store.sid = Product.sid
GROUP BY Store.sid, Store.name
HAVING 100 < min(Product.price)
SELECTStore.name
FROM Store
WHERE Store.sidNOTIN
(SELECTProduct.sid
FROM Product
WHERE Product.price
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Two Examples
Store(sid, sname)
Product(pid, pname, price, sid)
For each store,
find its most expensive product
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Two Examples
SELECTStore.sname, max(Product.price)
FROM Store, Product
WHERE Store.sid = Product.sid
GROUP BY Store.sid, Store.sname
SELECTStore.sname, x.pname
FROM Store, Product x
WHERE Store.sid = x.sid andx.price >=
ALL(SELECTy.price
FROMProduct y
WHEREStore.sid = y.sid)
This is easy but doesnt do what we want:
Better:
But mayreturn
multiple
product names
per store
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Two Examples
SELECTStore.sname, max(x.pname)
FROM Store, Product xWHERE Store.sid = x.sid and
x.price >=
ALL(SELECTy.price
FROMProduct yWHEREStore.sid = y.sid)
GROUP BYStore.sname
Finally, choose some pid arbitrarily, if there are manywith highest price:
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NULLS in SQL
Whenever we dont have a value, we can put a NULL
Can mean many things:
Value does not exists
Value exists but is unknown
Value not applicable
Etc.
The schema specifies for each attribute if can be null
(nullable attribute) or not How does SQL cope with tables that have NULLs ?
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Null Values
If x= NULL then 4*(3-x)/7 is still NULL
If x= NULL then x=Joe is UNKNOWN
In SQL there are three boolean values:
FALSE = 0
UNKNOWN = 0.5
TRUE = 1
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Null Values
C1 AND C2 = min(C1, C2)
C1 OR C2 = max(C1, C2)
NOT C1 = 1C1
Rule in SQL: include only tuples that yield TRUE
SELECT*FROMPersonWHERE (age < 25) AND
(height > 6 OR weight > 190)
E.g.
age=20
heigth=NULL
weight=200
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Null Values
Unexpected behavior:
Some Persons are not included !
SELECT*FROM Person
WHERE age < 25 OR age >= 25
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Null Values
Can test for NULL explicitly: x IS NULL
x IS NOT NULL
Now it includes all Persons
SELECT*FROM PersonWHERE age < 25 OR age >= 25 OR age IS NULL
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Outerjoins
Explicit joins in SQL = inner joins:Product(name, category)Purchase(prodName, store)
SELECTProduct.name, Purchase.store
FROM Product JOINPurchase ON
Product.name = Purchase.prodName
SELECTProduct.name, Purchase.store
FROM Product, Purchase
WHERE Product.name = Purchase.prodName
Same as:
But Products that never sold will be lost !
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Outerjoins
Left outer joins in SQL:
Product(name, category)
Purchase(prodName, store)
SELECTProduct.name, Purchase.store
FROM Product LEFT OUTER JOINPurchase ON
Product.name = Purchase.prodName
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Name Category
Gizmo gadget
Camera Photo
OneClick Photo
ProdName Store
Gizmo Wiz
Camera Ritz
Camera Wiz
Name Store
Gizmo Wiz
Camera Ritz
Camera Wiz
OneClick NULL
Product Purchase
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Application
Compute, for each product, the total number of sales in September
Product(name, category)
Purchase(prodName, month, store)
SELECTProduct.name, count(*)
FROM Product, Purchase
WHERE Product.name = Purchase.prodName
and Purchase.month = September
GROUP BY Product.name
Whats wrong ?
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Application
Compute, for each product, the total number of sales in September
Product(name, category)
Purchase(prodName, month, store)
SELECTProduct.name, count(*)
FROM Product LEFT OUTER JOINPurchase ON
Product.name = Purchase.prodName
and Purchase.month = SeptemberGROUP BY Product.name
Now we also get the products who sold in 0 quantity
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Outer Joins
Left outer join: Include the left tuple even if theres no match
Right outer join: Include the right tuple even if theres no match
Full outer join:
Include the both left and right tuples even if theres nomatch
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Modifying the Database
Three kinds of modifications
Insertions
Deletions
Updates
Sometimes they are all called updates
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Insertions
General form:
Missing attributeNULL.
May drop attribute names if give them in order.
INSERT INTO R(A1,., An) VALUES (v1,., vn)
INSERT INTO Purchase(buyer, seller, product, store)
VALUES (Joe, Fred, wakeup-clock-espresso-machine,
The Sharper Image)
Example: Insert a new purchase to the database:
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Insertions
INSERT INTO PRODUCT(name)
SELECT DISTINCT Purchase.product
FROM Purchase
WHERE Purchase.date > 10/26/01
The query replaces the VALUES keyword.
Here we insert manytuples into PRODUCT
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Insertion: an Example
prodNameis foreign key in Product.name
Suppose database got corrupted and we need to fix it:
name listPrice category
gizmo 100 gadgets
prodName buyerName price
camera John 200
gizmo Smith 80
camera Smith 225
Task: insert in ProductallprodNamesfrom Purchase
Product
Product(name, listPrice, category)
Purchase(prodName, buyerName, price)
Purchase
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Insertion: an Example
INSERT INTO Product(name)
SELECT DISTINCT prodName
FROM Purchase
WHERE prodName NOT IN(SELECT name FROM Product)
name listPrice category
gizmo 100 Gadgets
camera - -
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Insertion: an Example
INSERT INTO Product(name, listPrice)
SELECT DISTINCT prodName, price
FROM PurchaseWHERE prodName NOT IN(SELECT name FROM Product)
name listPrice category
gizmo 100 Gadgets
camera 200 -
camera ?? 225 ?? - Depends on the implementation
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Deletions
DELETE FROM PURCHASE
WHERE seller = Joe AND
product = Brooklyn Bridge
Factoid about SQL: there is no way to delete only a singleoccurrence of a tuple that appears twice
in a relation.
Example:
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Updates
UPDATE PRODUCT
SET price = price/2
WHERE Product.name IN(SELECTproduct
FROM Purchase
WHERE Date =Oct, 25, 1999);
Example: