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Writing Basic SQL SELECT Statements:

Writing Basic SQL SELECT Statements

Objectives:

Objectives After completing this lesson, you should be able to do the following: List the capabilities of SQL SELECT statements Execute a basic SELECT statement Differentiate between SQL statements and i SQL*Plus commands

Capabilities of SQL SELECT Statements:

Capabilities of SQL SELECT Statements Selection Projection Table 1 Table 2 Table 1 Table 1 Join

Basic SELECT Statement:

Basic SELECT Statement SELECT *|{[DISTINCT] column | expression [ alias ],...} FROM table; SELECT identifies what columns FROM identifies which table

Selecting All Columns:

SELECT * FROM departments; Selecting All Columns

Selecting Specific Columns:

Selecting Specific Columns SELECT department_id, location_id FROM departments;

Writing SQL Statements:

Writing SQL Statements SQL statements are not case sensitive. SQL statements can be on one or more lines. Keywords cannot be abbreviated or split across lines. Clauses are usually placed on separate lines. Indents are used to enhance readability.

Column Heading Defaults:

Column Heading Defaults i SQL*Plus: Default heading justification: Center Default heading display: Uppercase SQL*Plus: Character and Date column headings are left- justified Number column headings are right-justified Default heading display: Uppercase

Arithmetic Expressions:

Arithmetic Expressions Create expressions with number and date data by using arithmetic operators. Operator + - * / Description Add Subtract Multiply Divide

Using Arithmetic Operators:

Using Arithmetic Operators SELECT last_name, salary, salary + 300 FROM employees; …

Operator Precedence:

Operator Precedence Multiplication and division take priority over addition and subtraction. Operators of the same priority are evaluated from left to right. Parentheses are used to force prioritized evaluation and to clarify statements. * / + _

Operator Precedence:

Operator Precedence SELECT last_name, salary, 12*salary+100 FROM employees; …

Using Parentheses:

Using Parentheses SELECT last_name, salary, 12*(salary+100) FROM employees; …

Defining a Null Value:

Defining a Null Value A null is a value that is unavailable, unassigned, unknown, or inapplicable. A null is not the same as zero or a blank space. SELECT last_name, job_id, salary, commission_pct FROM employees; … …

Null Values in Arithmetic Expressions:

SELECT last_name, 12*salary*commission_pct FROM employees; Null Values in Arithmetic Expressions Arithmetic expressions containing a null value evaluate to null. … …

Defining a Column Alias:

Defining a Column Alias A column alias: Renames a column heading Is useful with calculations Immediately follows the column name - there can also be the optional AS keyword between the column name and alias Requires double quotation marks if it contains spaces or special characters or is case sensitive

Using Column Aliases:

Using Column Aliases SELECT last_name "Name", salary*12 "Annual Salary" FROM employees; SELECT last_name AS name, commission_pct comm FROM employees; … …

Concatenation Operator:

Concatenation Operator A concatenation operator: Concatenates columns or character strings to other columns Is represented by two vertical bars (||) Creates a resultant column that is a character expression

Using the Concatenation Operator:

Using the Concatenation Operator SELECT last_name||job_id AS "Employees" FROM employees; …

Literal Character Strings:

Literal Character Strings A literal is a character, a number, or a date included in the SELECT list. Date and character literal values must be enclosed within single quotation marks. Each character string is output once for each row returned.

Using Literal Character Strings:

Using Literal Character Strings SELECT last_name ||' is a '||job_id AS "Employee Details" FROM employees; …

Duplicate Rows:

Duplicate Rows The default display of queries is all rows, including duplicate rows. SELECT department_id FROM employees; …

Eliminating Duplicate Rows:

Eliminating Duplicate Rows Eliminate duplicate rows by using the DISTINCT keyword in the SELECT clause. SELECT DISTINCT department_id FROM employees;

SQL and iSQL*Plus Interaction:

SQL and i SQL*Plus Interaction SQL statements Oracle server Query results i SQL*Plus commands Client Formatted report Internet Browser i SQL*Plus

SQL Statements Versus iSQL*Plus Commands :

SQL Statements Versus i SQL*Plus Commands SQL statements SQL A language ANSI standard Keyword cannot be abbreviated Statements manipulate data and table definitions in the database i SQL*Plus An environment Oracle proprietary Keywords can be abbreviated Commands do not allow manipulation of values in the database Runs on a browser Centrally loaded, does not have to be implemented on each machine i SQL*Plus commands

Overview of iSQL*Plus:

Overview of i SQL*Plus After you log into i SQL*Plus, you can: Describe the table structure Edit your SQL statement Execute SQL from i SQL*Plus Save SQL statements to files and append SQL statements to files Execute statements stored in saved files Load commands from a text file into the i SQL*Plus Edit window

Logging In to iSQL*Plus:

Logging In to i SQL*Plus From your Windows browser environment:

The iSQL*Plus Environment:

The i SQL*Plus Environment 3 4 5 6 7 1 2 8 9 10

Displaying Table Structure:

Displaying Table Structure Use the i SQL*Plus DESCRIBE command to display the structure of a table. DESC[RIBE] tablename

Displaying Table Structure:

Displaying Table Structure DESCRIBE employees

Interacting with Script Files:

Interacting with Script Files SELECT last_name, hire_date, salary FROM employees; 1 2

Interacting with Script Files:

Interacting with Script Files 1 D:\temp\emp_sql.htm 2 SELECT last_name, hire_date, salary FROM employees; 3

Interacting with Script Files:

Interacting with Script Files DESCRIBE employees SELECT first_name, last_name, job_id FROM employees; 1 2 3

Summary:

Summary SELECT *|{[DISTINCT] column|expression [ alias ],...} FROM table; In this lesson, you should have learned how to: Write a SELECT statement that: Returns all rows and columns from a table Returns specified columns from a table Uses column aliases to give descriptive column headings Use the i SQL*Plus environment to write, save, and execute SQL statements and i SQL*Plus commands.

Practice 1 Overview:

Practice 1 Overview This practice covers the following topics: Selecting all data from different tables Describing the structure of tables Performing arithmetic calculations and specifying column names Using i SQL*Plus