basdat-2 sql select
TRANSCRIPT
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1Copyright Oracle Corporation, 2001. All rights reserved.
Writing BasicSQL SELECT Statements
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1-2 Copyright Oracle Corporation, 2001. All rights reserved.
Objectives
After completing this lesson, you should be able todo the following:
List the capabilities of SQL SELECT statements
Execute a basic SELECT statement Differentiate between SQL statements and
iSQL*Plus commands
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1-3 Copyright Oracle Corporation, 2001. All rights reserved.
Capabilities of SQL SELECT Statements
SelectionProjection
Table 1 Table 2
Table 1Table 1
Join
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1-4 Copyright Oracle Corporation, 2001. All rights reserved.
Basic SELECT Statement
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
SELECT identifies whatcolumns
FROMidentifies which table
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1-5 Copyright Oracle Corporation, 2001. All rights reserved.
SELECT *
FROM departments;
Selecting All Columns
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1-6 Copyright Oracle Corporation, 2001. All rights reserved.
Selecting Specific Columns
SELECT department_id, location_id
FROM departments;
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7/251-7 Copyright Oracle Corporation, 2001. All rights reserved.
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.
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Arithmetic Expressions
Create expressions with number and date data byusing arithmetic operators.
Operator
+
-
*
/
Description
Add
Subtract
Multiply
Divide
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Using Arithmetic Operators
SELECT last_name, salary, salary + 300
FROM employees;
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Operator Precedence
Multiplication and division take priority overaddition and subtraction.
Operators of the same priority are evaluated fromleft to right.
Parentheses are used to force prioritizedevaluation and to clarify statements.
*** /// +++ ___
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Operator Precedence
SELECT last_name, salary, 12*salary+100
FROM employees;
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Using Parentheses
SELECT last_name, salary, 12*(salary+100)
FROM employees;
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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_pctFROM employees;
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SELECT last_name, 12*salary*commission_pct
FROM employees;
Null Valuesin Arithmetic Expressions
Arithmetic expressions containing a null valueevaluate to null.
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Defining a Column Alias
A column alias:
Renames a column heading
Is useful with calculations
Immediately follows the column name - there canalso be the optionalAS keyword between thecolumn name and alias
Requires double quotation marks if it contains
spaces or special characters or is case sensitive
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Using Column Aliases
SELECT last_name "Name", salary*12 "Annual Salary"
FROM employees;
SELECT last_name AS name, commission_pct commFROM employees;
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Concatenation Operator
A concatenation operator:
Concatenates columns or character strings toother columns
Is represented by two vertical bars (||) Creates a resultant column that is a character
expression
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Literal Character Strings
A literal is a character, a number, or a dateincluded in the SELECT list.
Date and character literal values must be enclosed
within single quotation marks. Each character string is output once for eachrow returned.
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Using Literal Character Strings
SELECT last_name ||' is a '||job_id
AS "Employee Details"
FROM employees;
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Duplicate Rows
The default display of queries is all rows, includingduplicate rows.
SELECT department_id
FROM employees;
SELECT department_id
FROM employees;
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1-23 Copyright Oracle Corporation, 2001. All rights reserved.
Eliminating Duplicate Rows
Eliminate duplicate rows by using the DISTINCTkeyword in the SELECT clause.
SELECT DISTINCT department_id
FROM employees;
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1-29 Copyright Oracle Corporation, 2001. All rights reserved.
Displaying Table Structure
Use the iSQL*Plus DESCRIBE command to displaythe structure of a table.
DESC[RIBE] tablenameDESC[RIBE] tablename
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1-30 Copyright Oracle Corporation, 2001. All rights reserved.
Displaying Table Structure
DESCRIBE employeesDESCRIBE employees
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Summary
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
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 columnheadings
Use the iSQL*Plus environment to write, save, andexecute SQL statements and iSQL*Plus commands.