209 lines
5.3 KiB
Markdown
209 lines
5.3 KiB
Markdown
## Lecture 1 (13:00) - Relational Algebra
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### Data Manipulation Language
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- DML is a language providing a set of operations on the data of the database
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- Part of DML that involves data retrieval is called query language. One example is SQL
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#### #### Relational Calculus
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- Non-procedural language - declarative.
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- Used to formulate definition of relation in terms of one or more relations.
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- Specifies what is to be retrieved, rather than how.
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### Relational Algebra
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- High level procedural language
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- Used to tell DBMS how to build new relation from one or more relations in database
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#### Fundamental Operations
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##### SQL Overview
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##### Selection
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```
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U+03C3 <selection condition> (<relation name>)
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```
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- Selects a subset of the tuples in a relation that satisfy a selection condition.
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- sigma (lc) is used to specify a selection.
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- Selection condition is a bool expression, that includes AND, NOT, OR.
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- Result is a relation that has the same attributes as the relation that with the name specified.
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- ex.
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##### Projection
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- Selects a subset of the attributes of a relation.
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- Pi (uc) is used to define a projection
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- Order of attributes in the result is the same as that in the attribute list
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- Duplicate tuples are removed.
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- ex.
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##### Closure
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- Operations work on one or more relations to define another relation, without changing the original.
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- Both operands and results are relations.
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- Output from one operation can become the input from another.
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- Parallels algebraic operations in arithmetic, taking one or more numbers as operands, returning a number as output.
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- ex.
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- Select all staff with salary greater than 20000, and exclusively output the name.
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- Both input and output are relations.
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##### Unary and Binary Operations
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###### Unary Operations
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- Operate on one relation
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- Selection
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- Projection
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###### Binary Operations
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- Operate on two relations
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- Cartesian products
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- Union
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- Set difference
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##### Union
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- Union of 2 relations is a relation that contains all tuples of both.
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- Duplicates removed.
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- Both relations must be union compatible.
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- Resulting relation might have the same attributes as 1st or 2nd relation.
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- ex.
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###### Union Compatibility
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- Two relations R1(A1, A2,…. An) and R2(B1, B2,…. Bm) are union compatible if, and only if n = m and domain(Ai) = domain(Bi) for 1 =< i =< n.
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- It is rare that two relations are union compatible
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- Projection may be used to make two relations union compatible.
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###### Union with Projection
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- This is also an example of closure, as the output for the projection is used as the input for the union.
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##### Set Difference
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- In two relations, the set difference includes all tuples that are in one, but not the other.
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- Resulting relation may have the same attribute names as the first or second relation.
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- Must be union compatible.
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- ex.
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##### Cartesian Product
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- Relation which has concatenation of every tuple of first relation with every relation of the second.
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- If the 2 relations have attributes with the same name, attribute names are prefixed with the relations name.
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- ex.
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## Tutorial 2 (15:00) - Relational Algebra
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1. List the names and types of all boats
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- Relational Algebra
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**Pi** boat-name, boat-type (boats)
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```sql
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SELECT DISTINCT boat-name, boat-type
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FROM boats;
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```
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1. List the names of all pirates
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**Pi** name (Pirates)
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```sql
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SELECT DISTINCT p-name
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FROM pirates
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```
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1. List the names of all pirates who have less than two eyes
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**Pi** p-name ( **Sigma** eyes < 2 (pirates) )
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```sql
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SELECT DISTINCT names
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FROM pirates
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WHERE eyes < 2;
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```
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1. List the names of all pirates who have less than two eyes or less than two legs or both.
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**Pi** p-name ( **Sigma** eyes < 2 OR legs < 2 (pirates) )
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```sql
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SELECT DISTINCT names
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FROM pirates
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WHERE eyes < 2 OR legs < 2;
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```
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1. List all the places that either pirates or boats or both originate from
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**Pi** origin (pirates) **U** **Pi** origin (boats)
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```sql
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SELECT origin FROM pirates
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UNION
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SELECT origin FROM boats;
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```
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- NOTE: order matters, but only to the order in which they would appear in the list.
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1. List all the places where boats but not pirates originate from
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**Pi** origin (boats) - **Pi** origin (pirates)
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```sql
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SELECT origin FROM boats
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EXCEPT
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SELECT origin FROM pirates;
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```
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- NOTE: This specifically removes all places pirates originate from from the selection.
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## Workshop 1 (10:00)
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- Implement the two tables using the SQL CREATE TABLE command.
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```sql
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CREATE TABLE employee(
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empNo INTEGER PRIMARY KEY
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eName VARCHAR(20)
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sal INTEGER
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);
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```
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```sql
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CREATE TABLE manager(
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empNo INTEGER PRIMARY KEY
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eName VARCHAR(20)
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sal INTEGER
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);
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```
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- Write SQL statements that populate the two tables with the data shown.
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```sql
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INSERT INTO employee
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VALUES (7782, "clark", 2450), (7839, "king", 5000);
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```
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```sql
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INSERT INTO manager
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VALUES (8034, "smith", 7000),(8044, "yao", 6000);
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```
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- Write a single SQL query which returns all the staff from both of the tables.
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```sql
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SELECT empNo, eName
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FROM employee
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INNER JOIN manager
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ON employee.empNo = manager.empNo;
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```
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