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Lecture 4: Advanced SQL

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INTERSECT and EXCEPT:(missing from MySQL)

(SELECT R.A, R.BFROM R) INTERSECT(SELECT S.A, S.BFROM S)

(SELECT R.A, R.BFROM R) INTERSECT(SELECT S.A, S.BFROM S)

SELECT R.A, R.BFROM RWHERE EXISTS(SELECT * FROM S WHERE R.A=S.A and R.B=S.B)

SELECT R.A, R.BFROM RWHERE EXISTS(SELECT * FROM S WHERE R.A=S.A and R.B=S.B)

(SELECT R.A, R.BFROM R) EXCEPT(SELECT S.A, S.BFROM S)

(SELECT R.A, R.BFROM R) EXCEPT(SELECT S.A, S.BFROM S)

SELECT R.A, R.BFROM RWHERE NOT EXISTS(SELECT * FROM S WHERE R.A=S.A and R.B=S.B)

SELECT R.A, R.BFROM RWHERE NOT EXISTS(SELECT * FROM S WHERE R.A=S.A and R.B=S.B)

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Null Values

• NULL in SQL is used as a placeholder for a missing or unknown values

• By default, a table column can hold a NULL value

First Last Birth_Date Immigration_Date

Ola Hansen 1989/09/01 1992/08/31

Han Shin-Cho 1987/07/17 NULL

Joe NULL 1990/04/21 1999/11/23

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Use of 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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Three-Valued Logic• C1 AND C2 = min(C1, C2)• C1 OR C2 = max(C1, C2)• NOT C1 = 1 – C1

Rule in SQL: include only tuples that yield TRUE

SELECT *FROM PersonWHERE (age < 25) AND (height > 6 OR weight > 190)

SELECT *FROM PersonWHERE (age < 25) AND (height > 6 OR weight > 190)

E.g.age=20height=NULLweight=200

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Three-Valued Logic

Unexpected behavior:

Some Persons are not included !

SELECT *FROM PersonWHERE age < 25 OR age >= 25

SELECT *FROM PersonWHERE age < 25 OR age >= 25

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Working with 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

SELECT *FROM PersonWHERE age < 25 OR age >= 25 OR age IS NULL

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Explicit JoinsExplicit joins in SQL:

Product(name, category) Purchase(prodName, store)

Same as:

But Products that never sold will be lost !

SELECT Product.name, Purchase.storeFROM Product JOIN Purchase ON Product.name = Purchase.prodName

SELECT Product.name, Purchase.storeFROM Product JOIN Purchase ON Product.name = Purchase.prodName

SELECT Product.name, Purchase.storeFROM Product, PurchaseWHERE Product.name = Purchase.prodName

SELECT Product.name, Purchase.storeFROM Product, PurchaseWHERE Product.name = Purchase.prodName

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Left Outer Joins

Left outer joins in SQL:Product(name, category)

Purchase(prodName, store)

SELECT Product.name, Purchase.store FROM Product LEFT OUTER JOIN Purchase ON Product.name = Purchase.prodName

SELECT Product.name, Purchase.store FROM Product LEFT OUTER JOIN Purchase 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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Types of Joins - Summary

• Inner join: same as Join, implicit Join• Left outer join:

– Same as Left join– Include the left tuple even if there’s no match

• Right outer join:– Same as right join– Include the right tuple even if there’s no match

• Full outer join:– Missing from MySQL (but can be emulated! how?)– Include the both left and right tuples even if there’s no match

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Modifying the Database

Three kinds of modifications• Insertions• Deletions• Updates

Sometimes they are all called “updates”

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InsertionsGeneral form:

Missing attributes NULL.May drop attribute names if give them in order.

INSERT INTO R(A1,…., An) VALUES (v1,…., vn) 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’)

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”

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 many tuples into PRODUCT

The number of columns must be identical

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Insertion: an Example

prodName is 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 Product all prodNames from Purchase

Product

Product(name, listPrice, category)Purchase(prodName, buyerName, price)

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)

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 Purchase WHERE prodName NOT IN (SELECT name FROM Product)

INSERT INTO Product(name, listPrice)

SELECT DISTINCT prodName, price FROM Purchase WHERE prodName NOT IN (SELECT name FROM Product)

name listPrice category

gizmo 100 Gadgets

camera 200 -

camera ?? 225 ?? - ERROR!

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Deletions

DELETE FROM PURCHASE

WHERE seller = ‘Joe’ AND product = ‘Brooklyn Bridge’

DELETE FROM PURCHASE

WHERE seller = ‘Joe’ AND product = ‘Brooklyn Bridge’

Factoid about SQL: there is no way to delete only xoccurrences of a tuple that appears x+k times in a relation.

Example:

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Updates

UPDATE ProductSET listPrice= listPrice/2WHERE Product.name IN (SELECT product FROM Purchase WHERE Date =‘Oct, 25, 1999’);

UPDATE ProductSET listPrice= listPrice/2WHERE Product.name IN (SELECT product FROM Purchase WHERE Date =‘Oct, 25, 1999’);

Example:

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Updates Using Exists

UPDATE ProductSET listPrice = (SELECT AVG(price)

FROM PurchaseWHERE prodName=name)

WHERE EXISTS (SELECT *FROM PurchaseWHERE prodName=name);

UPDATE ProductSET listPrice = (SELECT AVG(price)

FROM PurchaseWHERE prodName=name)

WHERE EXISTS (SELECT *FROM PurchaseWHERE prodName=name);

Example:

Table Modifications - Summary

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INSERT INTO table_name (column1, column2,...)VALUES (value1, value2, ...)

INSERT INTO table_name (column1, column2,...)VALUES (value1, value2, ...)

INSERT INTO table_name (column1, column2,...)SELECT …

INSERT INTO table_name (column1, column2,...)SELECT …

DELETE FROM table_name WHERE cond

DELETE FROM table_name WHERE cond

UPDATE table_nameSET column1=expr1, column2=expr2,...WHERE cond

UPDATE table_nameSET column1=expr1, column2=expr2,...WHERE cond