ORACLE官方基础教程第1讲(经典版)

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Copyright © Oracle Corporation, 2001. All rights reserved.
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.
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Copyright © Oracle Corporation, 2001. All rights reserved.
Column Heading Defaults
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iSQL*Plus:
– – Default heading justification: Center Default heading display: Uppercase Character and Date column headings are leftjustified Number column headings are right-justified Default heading display: Uppercase
• List the capabilities of SQL SELECT statements • Execute a basic SELECT statement • Differentiate between SQL statements and
iSQL*Plus commands
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Copyright © Oracle Corporation, 2001. All rights reserved.
Capabilities of SQL SELECT Statements
Projection
Selection
Table 1 Join
Table 1
Table 1
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Table 2
Copyright © Oracle Corporation, 2001. All rights reserved.
Basic SELECT Statement
SELECT FROM
*|{[DISTINCT] column|expression [alias],...} table;
• •
SELECT identifies what columns
FROM identifies which table
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Copyright © Oracle Corporation, 2001. All rights reserved.
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Copyright © Oracle Corporation, 2001. All rights reserved.
Concatenation Operator
A concatenation operator:
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Concatenates columns or character strings to other columns
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Copyright © Oracle Corporation, 2001. All rights reserved.
Writing SQL Statements
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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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Copyright © Oracle Corporation, 2001. All rights reserved.
Using Literal Character Strings
SELECT last_name ||' is a '||job_id AS "Employee Details" FROM employees;
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Copyright © Oracle Corporation, 2001. All rights reserved.
Eliminating Duplicate Rows
Eliminate duplicate rows by using the DISTINCT keyword in the SELECT clause.
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Requires double quotation marks if it contains spaces or special characters or is case sensitive
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Copyright © Oracle Corporation, 2001. All rights reserved.
Internet Browser
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Copyright © Oracle Corporation, 2001. All rights reserved.
Operator Precedence
SELECT last_name, salary, 12*salary+100 FROM employees;
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Copyright © Oracle Corporation, 2001. All rights reserved.
Using Column Aliases
SELECT last_name AS name, commission_pct comm FROM employees;
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SELECT last_name "Name", salary*12 "Annual Salary" FROM employees;
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SELECT DISTINCT department_id FROM employees;
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Copyright © Oracle Corporation, 2001. All rights reserved.
SQL and iSQL*Plus Interaction
iSQL*Plus
SQL statements
SELECT last_name, 12*salary*commission_pct FROM employees;
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Copyright © Oracle Corporation, 2001. All rights reserved.
Defining a Column Alias
A column alias:
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Copyright © Oracle Corporation, 2001. All rights reserved.
Duplicate Rows
The default display of queries is all rows, including duplicate rows.
SELECT department_id FROM employees;
Writing Basic SQL SELECT Statements
Copyright © Oracle Corporation, 2001. All rights reserved.
Objectives
After completing this lesson, you should be able to do the following:
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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;
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Copyright © Oracle Corporation, 2001. All rights reserved.
Null Values in Arithmetic Expressions
Arithmetic expressions containing a null value evaluate to null.
Using the Concatenation Operator
SELECT FROM
last_name||job_id AS "Employees" employees;
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Copyright © Oracle Corporation, 2001. All rights reserved.
•
SQL*Plus:
– – –
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Copyright © Oracle Corporation, 2001. All rights reserved.
Arithmetic Expressions
Create expressions with number and date data by using arithmetic operators.