Nesting Functions

Nesting Functions

• Single-row functions can be nested to any level.
• Nested functions are evaluated from deepest level to the least deep level.

General Functions

These functions work with any data type and pertain to using null value.
• NVL (expr1, expr2)
• NVL2 (expr1, expr2, expr3)
• NULLIF (expr1, expr2)
• COALESCE (expr1, expr2, ..., exprn).

NVL Function

• Converts a null to an actual value.
• Data types that can be used are date, character, and number.
• Data types must match:
– NVL(commission_pct,0)
– NVL(hire_date,'01-JAN-97')
– NVL(job_id,'No Job Yet')

Using the NVL Function

Using the NVL2 Function

Using the NULLIF Function

Using the COALESCE Function

• The advantage of the COALESCE function over the NVL function is that the COALESCE function can take multiple alternate values.
• If the first expression is not null, it returns that expression; otherwise, it does a COALESCE of the remaining expressions.

Using the COALESCE Function

Conditional Expressions

• Give you the use of IF-THEN-ELSE logic within a SQL statement
• Use two methods:
– CASE expression
– DECODE function

The CASE Expression

Facilitates conditional inquiries by doing the work of an IF-THEN-ELSE statement:

Using the CASE Expression

Facilitates conditional inquiries by doing the work of an IF-THEN-ELSE statement:

The DECODE Function

Facilitates conditional inquiries by doing the work of a CASE or IF-THEN-ELSE statement:

Using the DECODE Function.

Display the applicable tax rate for each employee in department 80.

Other useful Links :

• http://www.developerchoice.com/

• http://www.sqlserverquestions.blogspot.com
  

Conversion Functions

Overview

This practice covers the following topics:
• Writing a query that displays the current date
• Creating queries that require the use of numeric, character, and date functions.

Implicit Data-Type Conversion

For assignments, the Oracle server can automatically convert the following:
For expression evaluation, the Oracle Server can automatically convert the following:

Explicit Data-Type Conversion


Using the TO_CHAR Function with Dates

The format model:
• Must be enclosed in single quotation marks and is case sensitive
• Can include any valid date format element
• Has an fm element to remove padded blanks or suppress leading zeros
• Is separated from the date value by a comma.

Elements of the Date Format Model

• Time elements format the time portion of the date.

• Add character strings by enclosing them in double quotation marks.
• Number suffixes spell out numbers.

Using the TO_CHAR Function with Dates


Using the TO_CHAR Function with Numbers

These are some of the format elements you can use with the TO_CHAR function to display a number value as a character:

Using the TO_NUMBER and TO_DATE Functions

• Convert a character string to a number format using the TO_NUMBER function:
• Convert a character string to a date format using the TO_DATE function:
• These functions have an fx modifier. This modifier specifies the exact matching for the character argument and date format model of a TO_DATE function.

RR Date Format
Example of RR Date Format

Single-Row Functions

Objectives

After completing this lesson, you should be able to do the following:
• Describe various types of functions available in SQL
• Use character, number, and date functions in SELECT statements
• Describe the use of conversion functions.

SQL Functions


Two Types of SQL Functions

Single-Row Functions

Single row functions:
• Manipulate data items
• Accept arguments and return one value
• Act on each row returned
• Return one result per row
• May modify the data type
• Can be nested
• Accept arguments which can be a column or an expression.

Character Functions

Case Manipulation Functions
These functions convert case for character strings.

Using Case Manipulation Functions

Display the employee number, name, and department number for employee Higgins:

Character-Manipulation Functions
These functions manipulate character strings:


Using the Character-Manipulation Functions


Number Functions
• ROUND: Rounds value to specified decimal
• TRUNC: Truncates value to specified decimal
• MOD: Returns remainder of division


Using the ROUND Function

DUAL is a dummy table you can use to view results from functions and calculations.

Using the TRUNC Function

Using the MOD Function

Calculate the remainder of a salary after it is divided by 5000 for all employees whose job title is sales representative.

Working with Dates

• Oracle database stores dates in an internal numeric format: century, year, month, day, hours,
minutes, seconds.
• The default date display format is DD-MON-RR.
– Allows you to store 21st century dates in the 20th century by specifying only the last two digits of the year.
– Allowa you to store 20th century dates in the 21st century in the same way.

SYSDATE is a function that returns:
• Date
• Time

Arithmetic with Dates

• Add or subtract a number to or from a date for a resultant date value.
• Subtract two dates to find the number of days between those dates.
• Add hours to a date by dividing the number of hours by 24.

Using Arithmetic Operators with Dates

Date Functions

Restricting and Sorting Data

Objectives

After completing this lesson, you should be able to do the following:
• Limit the rows retrieved by a query
• Sort the rows retrieved by a query

Limiting Rows Using a Selection

Limiting the Rows Selected

• Restrict the rows returned by using the WHERE clause.
• The WHERE clause follows the FROM clause.

Using the WHERE Clause

Character Strings and Dates

• Character strings and date values are enclosed in single quotation marks.
• Character values are case sensitive, and date values are format sensitive.
• The default date format is DD-MON-RR.

Comparison Conditions

Using Comparison Conditions
Other Comparison Conditions

Using the BETWEEN Condition

Using the IN Condition

Using the LIKE Condition

• Use the LIKE condition to perform wild card searches of valid search string values.
• Search conditions can contain either literal characters or numbers:

– % denotes zero or many characters.

– _ denotes one character.
• You can combine pattern-matching characters.
• You can use the ESCAPE identifier to search for the actual % and _ symbols.

Using the NULL Conditions

Test for nulls with the IS NULL operator.

Logical Conditions

Using the AND Operator

AND requires both conditions to be true.

Using the OR Operator

OR requires either condition to be true.

Using the NOT Operator

Rules of Precedence

Override rules of precedence by using parentheses.

Use parentheses to force priority.

ORDER BY Clause

• Sort rows with the ORDER BY clause
– ASC: ascending order (the default order)
– DESC: descending order
• The ORDER BY clause comes last in the SELECT statement.

Sorting in Descending Order

Sorting by Column Alias

Sorting by Multiple Columns

• The order of ORDER BY list is the order of sort.
• You can sort by a column that is not in the SELECT list.

Summary

In this, you should have learned how to:

• Use the WHERE clause to restrict rows of output
– Use the comparison conditions
– Use the BETWEEN, IN, LIKE, and NULL conditions
– Apply the logical AND, OR, and NOT operators

• Use the ORDER BY clause to sort rows of output