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Questions and Answers

What are the two major components of SQL?

SQL has two major components: a Data Definition Language (DDL) for defining the database structure and a Data Manipulation Language (DML) for retrieving and updating data.

What type of commands does SQL lack?

SQL lacks flow control commands such as IF...THEN … ELSE, GOTO, WHILE … DO.

What are the four Data Manipulation Language (DML) statements in SQL?

The four DML statements in SQL are: SELECT, INSERT, UPDATE, and DELETE.

What columns does the Stock Item Relation table have?

The Stock Item Relation table has columns for stock code, stock name, minimum stock level, sale price, and amount in hand. Signup and view all the answers

What columns does the Sales Relation table have?

The Sales Relation table has columns for date, branch numbers, stock code, and quantity sold. Signup and view all the answers

What columns does the Branches Relation table have?

The Branches Relation table has columns for branch code, branch name, and town. Signup and view all the answers

What is the purpose of the WHERE clause in a SQL statement?

To filter records that satisfy a specified condition Signup and view all the answers

What is the purpose of the AND, OR, and NOT logical operators in conditional statements?

To generate more complex predicates Signup and view all the answers

What is the order of evaluation for conditional expressions in SQL?

Left to right, with expressions in brackets evaluated first, followed by NOT, then AND, and finally OR Signup and view all the answers

What is the purpose of the BETWEEN operator in a SQL statement?

To select records that fall within a specified range of values Signup and view all the answers

What is the purpose of the SELECT statement in a SQL query?

To specify the columns that should be retrieved from a database table Signup and view all the answers

What is the purpose of the FROM clause in a SQL statement?

To specify the database table(s) to retrieve data from Signup and view all the answers

How do you specify multiple conditions in a WHERE clause?

Using the AND, OR, and NOT logical operators Signup and view all the answers

What is the purpose of the OR operator in a WHERE clause?

To select records that satisfy at least one of the specified conditions Signup and view all the answers

What does the LIKE operator `%e` match in a string?

Any sequence of characters of length at least 1 with the last character an 'e' Signup and view all the answers

What does the condition `Address LIKE '%Nicosia%'` match?

A sequence of characters of any length containing 'Nicosia' Signup and view all the answers

What does the condition `Address NOT LIKE 'H%'` mean?

The first character cannot be 'H' Signup and view all the answers

What is the purpose of the `IS NULL` condition?

To check if a field has a null value Signup and view all the answers

What is the minimum stock level for the monitor with code MON 15?

4 Signup and view all the answers

What is the effect of adding `ASC` to an `ORDER BY` clause?

The results are sorted in ascending order Signup and view all the answers

How many CDWR were sold on 1/12/03?

17 Signup and view all the answers

How can you sort a query by multiple columns?

By listing the column names separated by commas in the <code>ORDER BY</code> clause Signup and view all the answers

Which branch is located in Nicosia?

B1 (Shopping Center Branch) Signup and view all the answers

What is the price of a 20 GB Disk (DIS 20)?

$90 Signup and view all the answers

What is the purpose of the `LIKE` operator with a wildcard?

To search for patterns in strings Signup and view all the answers

What is the purpose of the `IS NOT NULL` condition?

To check if a field has a non-null value Signup and view all the answers

How many KEY 04 were sold on 3/12/03?

3 Signup and view all the answers

What is the primary purpose of the SELECT statement in SQL?

To retrieve and display data from one or more database tables. Signup and view all the answers

What is the current stock level of the Main Board (MB 100)?

0 Signup and view all the answers

In the SELECT statement, what clause is used to filter rows based on certain conditions?

WHERE Signup and view all the answers

Which item has the lowest sale price?

MS 10 (Mouse) at $9 Signup and view all the answers

How many CD 52 were sold on 2/12/03?

2 Signup and view all the answers

What are the two mandatory clauses in the SELECT statement?

SELECT and FROM Signup and view all the answers

What is the purpose of the GROUP BY clause in the SELECT statement?

To form groups of rows with the same column value. Signup and view all the answers

What is the difference between the WHERE and HAVING clauses in the SELECT statement?

The WHERE clause filters rows, while the HAVING clause filters groups. Signup and view all the answers

How can you retrieve all columns in a table using the SELECT statement?

Using the asterisk symbol (*) Signup and view all the answers

Study Notes

Search Conditions

In conditional statements, the following logical operators are used:
- = (Equals)
- < (Less than)
- > (Greater than)
- ≤ (Less than or equal)
- ≥ (Greater than or equal)
- ≠ (Not equal to)
More complex predicates can be generated using AND, OR, and NOT.
The rule of evaluation for conditional expressions is:
- Expressions are evaluated left to right
- Expressions inserted in brackets are evaluated first
- NOTs are evaluated before ANDs and ORs
- ANDs are evaluated before ORs

Compound Comparisons

Example: List all sales of 64 MB VGA or Keyboard by Sales-Date, Branch-Number, Stock-Code
The result shows the sales of 64 MB VGA or Keyboard by Sales-Date, Branch-Number, Stock-Code

Range Search Condition (BETWEEN / NOT BETWEEN)

Example: List all stocks whose Stock-Quantity is between 5 and 50 by Stock-Code, Stock-Quantity
The SQL statement uses the BETWEEN operator to filter the results

Structured Query Language (SQL)

SQL is a transform-oriented and non-procedure language designed to use relations to transform inputs into required outputs
SQL has two major components:
- A Data Definition Language (DDL) for defining the database structure
- A Data Manipulation Language (DML) for retrieving and updating data
SQL contains only definitional and manipulative commands, and does not contain flow control commands
SQL can be used in two ways:
- Use SQL interactively by entering the statements at the terminal
- Embed SQL statements in a procedural language

SQL DML Statements

Data manipulation statements in SQL are:
- SELECT: To query data in the database
- INSERT: To insert data into a table
- UPDATE: To update data in a table
- DELETE: To delete data from a table

SELECT Statement

The purpose of the SELECT statement is to retrieve and display data from one or more database tables
The general format of the SELECT statement is:

SELECT [DISTENCT/ALL] {*/[Column – Expression]}
FROM Table name(s)
[WHERE condition]
[GROUP BY Column – list][HAVING Condition]
[ORDER BY Column – list]

The SELECT statement is extremely powerful and can perform the equivalent of relational algebra's selection, projection, and join in a single statement
The order of the clauses in the SELECT statement cannot be changed

Null Search Condition (IS NULL/IS NOT NULL)

Example: List the entries in the Sales where there is no date entry
The result shows the entries in the Sales where there is no date entry

Sorting the Results (ORDER BY)

The sorting may be in ASC (ascending) or DESC (descending) order
The sorting may be used on single column or multiple columns

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