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Questions and Answers
What is the purpose of the condition 'A.Nr < B.Nr' in the SQL query for retrieving names of executors with the same qualification?
What is the purpose of the condition 'A.Nr < B.Nr' in the SQL query for retrieving names of executors with the same qualification?
It is used to eliminate duplicate results by ensuring that each pair of names is listed only once.
In SQL, how can you retrieve the names of executors participating in project number 1?
In SQL, how can you retrieve the names of executors participating in project number 1?
You can use the query: SELECT Pavarde FROM Vykdytojai WHERE Nr IN (SELECT Vykdytojas FROM Vykdymas WHERE Projektas = 1)
.
What is the purpose of the CREATE TABLE
statement in SQL?
What is the purpose of the CREATE TABLE
statement in SQL?
To define a new table and its columns in a database.
What is the difference between CHAR(n)
and VARCHAR(n)
in SQL?
What is the difference between CHAR(n)
and VARCHAR(n)
in SQL?
What is a primary key in a database?
What is a primary key in a database?
Provide an example SQL statement to create a primary key on a column 'ID' in a table 'TEST'.
Provide an example SQL statement to create a primary key on a column 'ID' in a table 'TEST'.
Explain what the NOT NULL
constraint does in a table definition.
Explain what the NOT NULL
constraint does in a table definition.
What does the DEFAULT
keyword specify in a table definition?
What does the DEFAULT
keyword specify in a table definition?
What is the function of a foreign key in a relational database?
What is the function of a foreign key in a relational database?
How do you create an index on a column 'Pavarde' in the table 'Vykdytojai'?
How do you create an index on a column 'Pavarde' in the table 'Vykdytojai'?
Describe the use of AUTO_INCREMENT
in a SQL table.
Describe the use of AUTO_INCREMENT
in a SQL table.
What data type would you use to store a decimal value in SQL, and how is it defined?
What data type would you use to store a decimal value in SQL, and how is it defined?
Explain why it is not advisable to index frequently changing columns in a database.
Explain why it is not advisable to index frequently changing columns in a database.
What is database design and why is it important?
What is database design and why is it important?
What does the UNIQUE
constraint ensure for a column in a table?
What does the UNIQUE
constraint ensure for a column in a table?
Identify the SQL data type suitable for storing date and time values.
Identify the SQL data type suitable for storing date and time values.
Explain the purpose of the ALTER TABLE statement in SQL.
Explain the purpose of the ALTER TABLE statement in SQL.
What is the key difference between using WHERE and JOIN in SQL queries?
What is the key difference between using WHERE and JOIN in SQL queries?
What is meant by the 'JOIN condition' in SQL?
What is meant by the 'JOIN condition' in SQL?
Describe the output of an INNER JOIN.
Describe the output of an INNER JOIN.
What is the effect of using a LEFT OUTER JOIN?
What is the effect of using a LEFT OUTER JOIN?
In a query to retrieve project managers, how would you include managers not involved in any projects using JOIN?
In a query to retrieve project managers, how would you include managers not involved in any projects using JOIN?
Explain the function of FULL OUTER JOIN in database queries.
Explain the function of FULL OUTER JOIN in database queries.
How can tables be joined with themselves, and why would this be useful?
How can tables be joined with themselves, and why would this be useful?
What are the three essential questions to consider when starting to create a database?
What are the three essential questions to consider when starting to create a database?
Why is it said that not planning a database can lead to wasting more time later?
Why is it said that not planning a database can lead to wasting more time later?
List the types of tables needed for a library database.
List the types of tables needed for a library database.
What is the role of primary keys in database tables?
What is the role of primary keys in database tables?
How should data fields in tables be determined?
How should data fields in tables be determined?
Explain the principle regarding the repetition of information in database tables.
Explain the principle regarding the repetition of information in database tables.
What data does a library database need to track about its books?
What data does a library database need to track about its books?
What happens after defining the database's purpose?
What happens after defining the database's purpose?
What is the role of primary keys in establishing relationships between tables in a database?
What is the role of primary keys in establishing relationships between tables in a database?
Explain the purpose of database normalization.
Explain the purpose of database normalization.
What distinguishes the first normal form (1NF) from unnormalized data?
What distinguishes the first normal form (1NF) from unnormalized data?
Characterize the significance of moving non-key-dependent information into separate tables.
Characterize the significance of moving non-key-dependent information into separate tables.
In what scenario might a 1:1 relationship be utilized in a database?
In what scenario might a 1:1 relationship be utilized in a database?
Define the third normal form (3NF) in the context of database normalization.
Define the third normal form (3NF) in the context of database normalization.
Why is it important to check for potential flaws in a database structure after initial creation?
Why is it important to check for potential flaws in a database structure after initial creation?
What is the role of foreign keys in a relational database?
What is the role of foreign keys in a relational database?
Flashcards
CREATE TABLE statement
CREATE TABLE statement
Used to create a database table in SQL.
Database data types
Database data types
Types of data a database can store, such as text, numbers, dates, and binary.
VARCHAR(n)
VARCHAR(n)
Variable-length character string data type (e.g., a person's name).
INTEGER data type
INTEGER data type
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NOT NULL constraint
NOT NULL constraint
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AUTO_INCREMENT
AUTO_INCREMENT
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UNIQUE constraint
UNIQUE constraint
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DECIMAL(p, s)
DECIMAL(p, s)
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SQL ALTER TABLE
SQL ALTER TABLE
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Table JOIN
Table JOIN
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INNER JOIN
INNER JOIN
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LEFT OUTER JOIN
LEFT OUTER JOIN
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RIGHT OUTER JOIN
RIGHT OUTER JOIN
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JOIN condition
JOIN condition
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Multiple Table JOINs
Multiple Table JOINs
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SQL SELECT statement
SQL SELECT statement
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Primary Key
Primary Key
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Foreign Key
Foreign Key
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Indexes
Indexes
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SQL JOIN
SQL JOIN
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SQL SELECT
SQL SELECT
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Database Design
Database Design
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SQL WHERE clause
SQL WHERE clause
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SQL IN operator
SQL IN operator
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Database Design Process
Database Design Process
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Database Purpose
Database Purpose
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Database Table
Database Table
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Table Field
Table Field
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Unique Field
Unique Field
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Table Relationship
Table Relationship
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Atomic Concept
Atomic Concept
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Multi-field Key
Multi-field Key
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Database Normalization
Database Normalization
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1NF (First Normal Form)
1NF (First Normal Form)
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2NF (Second Normal Form)
2NF (Second Normal Form)
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3NF (Third Normal Form)
3NF (Third Normal Form)
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Relationship Types
Relationship Types
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Study Notes
Database Usage, SQL
- Databases use SQL for data management.
- SQL is used to design databases.
Table Creation
- Tables are created using
CREATE TABLE
statements. - The structure follows:
CREATE TABLE table_name (column1 type1, column2 type2, ...)
- Supported data types include:
- Textual data
- Binary data
- Numbers
- Dates
- Times
Character Data Types
- Character strings can hold a specific number of characters.
- Fixed-length strings:
CHAR(n)
-n
characters up to 254 (2,147,483,647).
- Variable-length strings:
VARCHAR(n)
orCHARACTER VARYING(n)
-n
characters, up to 2,147,483,647.CLOB(n[K|M|G])
- up to 2 GB.
Numeric Data Types
- Integer types:
SMALLINT
: Integer values from -32,768 to 32,767.INTEGER
(4 bytes): Integer values from -2,147,483,648 to 2,147,483,647.BIGINT
(8 bytes): Larger integer values.
- Floating-point types:
REAL
(32 bytes): Floating-point numbers.FLOAT
orDOUBLE
: Larger floating-point values.
- Decimal:
DECIMAL (p, s)
orNUMERIC
: Stores decimal numbers with precisionp
and scales
Binary Data Types
- Fixed-length binary data:
BINARY(n)
- up to 1 billion bytes.
- Variable-length binary data:
VARBINARY(n)
- up to 1 billion bytes.BLOB(n[K|M|G])
- up to 2 GB.
Dates and Times
DATE
: Stores dates.TIME
: Stores time values.TIMESTAMP
: Stores both date and time.
Table Creation (Examples)
- Example
CREATE TABLE
statement for employees:CREATE TABLE Employees (EmployeeID BIGINT NOT NULL, FirstName VARCHAR(20), LastName VARCHAR(30), HireDate DATE, Salary DECIMAL(10, 2) DEFAULT 0)
Table Modifications
ALTER TABLE
statements allow modifying existing tables- Add a column:
ALTER TABLE table_name ADD column_name data_type
- Drop a column:
ALTER TABLE table_name DROP column_name
- Change column properties:
ALTER TABLE table_name ALTER column_name SET DEFAULT value
Table Joins (WHERE)
WHERE
clauses are used to filter data from joins.SELECT column1, column2 FROM table1, table2 WHERE condition
.
Table Joins (JOIN)
- Different ways to combine data from multiple tables
JOIN
simplifies conditions from multiple tables.- Uses
ON
clause, e.g.,SELECT column1, column2 FROM table1 JOIN table2 ON table1.columnX = table2.columnY
.
Structured Queries
- Structured query language statements often use subqueries
IN
operator is used in selecting values from a subquery
Primary Keys
- Ensure unique identification of rows in a table.
- The
PRIMARY KEY
constraint prevents duplicate values. - Examples:
CREATE TABLE Customers (CustomerID INT PRIMARY KEY, ...)
ALTER TABLE Orders ADD CONSTRAINT pk_order PRIMARY KEY (OrderID)
Foreign Keys
- Foreign keys create a link between two tables.
- A foreign key references a primary key in a foreign table.
ALTER TABLE Orders ADD CONSTRAINT fk_order_customer FOREIGN KEY (CustomerID) REFERENCES Customers (CustomerID) ON DELETE CASCADE
Indexes
- Data structures used for faster lookups in databases.
- Indexes enhance search speed.
- They are useful for large databases.
- Useful for speeding up the lookups of data.
CREATE INDEX idx_name ON table_name(column_name)
DROP INDEX idx_name
Database Design
- Designing a database is crucial before actually creating it
- Consider the purpose, data requirements, and user needs
Database Design Process
- Define the database purpose
- Identify required tables
- Define column data types
- Determine relationships between tables
- Refine the initial design
Database Purpose
- Clarify what the database will track.
- Specify the data users will need.
- Detail data manipulation requests.
Table Definitions
- Define entities and attributes.
- Aim for each table representing one object.
- Avoid redundant information in one table.
- Should be related in a database.
Data Elements in Tables
- Determine data attributes for each object.
- Keep data elements concise.
Database Normalization
- Reduce redundant data and dependency issues.
- Create separate tables for related data
- Normalization processes include Normal forms (1NF, 2NF, 3NF, BCNF, 4NF, 5NF) to ensure logical and data organization
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Description
This quiz covers the fundamentals of SQL usage in database management, including how to create tables and understand various data types. It explores character and numeric data types, providing essential knowledge for database design and implementation.