computer notes - Writing Basic SQL SELECT Statements
-
Upload
ecomputernotes -
Category
Documents
-
view
220 -
download
0
Transcript of computer notes - Writing Basic SQL SELECT Statements
-
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
1/23
Basic SELECT Statement
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
2/23
SELECT
FROM
Basic SELECT Statement
* | { [DISTINCT] column|expression[alias],...}table;
SELECTidentifieswhatcolumns
FROMidentifieswhichtable
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
3/23
SELECT *
Selecting All Columns
FROM departments;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
4/23
Selecting Specific Columns
SELECT department_id, location_id
FROM departments;
http://ecomputernotes.com
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
5/23
Writing SQL Statements
SQL statements are not case sensitive.
SQL statements can be on one or more lines.
Keywords cannot be abbreviated or splitacross lines.
Clauses are usually placed on separate lines.
Indents are used to enhance readability.
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
6/23
Column Heading Defaults
iSQL*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
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
7/23
Arithmetic Expressions
Create expressions with number and date data byusing arithmetic operators.
Operator
+
-
*
/
Description
Add
Subtract
Multiply
Divide
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
8/23
Using Arithmetic Operators
SELECT last_name, salary, salary + 300
FROM employees;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
9/23
Operator Precedence
* / +_
Multiplication and division take priority over
addition and subtraction.Operators of the same priority are evaluated fromleft to right.
Parentheses are used to force prioritizedevaluation and to clarify statements.
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
10/23
Operator Precedence
SELECT last_name, salary, 12*salary+100
FROM employees;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
11/23
Using Parentheses
SELECT last_name, salary, 12*(salary+100)
FROM employees;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
12/23
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;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
13/23
Null Values
in Arithmetic Expressions
Arithmetic expressions containing a null valueevaluate to null.
SELECT last_name, 12*salary*commission_pct
FROM employees;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
14/23
Defining a Column Alias
A column alias:
Renames a column heading
Is useful with calculations
Immediately follows the column name - there canalso be the optionalASkeyword between thecolumn name and alias
Requires double quotation marks if it containsspaces or special characters or is case sensitive
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
15/23
Using Column Aliases
SELECT last_name AS name, commission_pct comm
FROM employees;
SELECT last_name "Name", salary*12 "Annual Salary"
FROM employees;
http://ecomputernotes.com
.
http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
16/23
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 characterexpression
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
17/23
Using the Concatenation Operator
SELECT
FROM
last_name||job_id AS "Employees"
employees;
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
18/23
Literal Character Strings
A literal is a character, a number, or a dateincluded in theSELECTlist.
Date and character literal values must be enclosed
within single quotation marks.Each character string is output once for eachrow returned.
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
19/23
Using Literal Character Strings
SELECT last_name ||' is a '||job_id
AS "Employee Details"
FROM employees;
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
20/23
Duplicate Rows
The default display of queries is all rows, including
duplicate rows.
SELECT department_id
FROM employees;
.
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
21/23
Eliminating Duplicate Rows
Eliminate duplicate rows by using theDISTINCTkeyword in theSELECTclause.
SELECT DISTINCT department_id
FROM employees;
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
22/23
Displaying Table Structure
DESCRIBE employees
http://ecomputernotes.com/http://ecomputernotes.com/ -
8/3/2019 computer notes - Writing Basic SQL SELECT Statements
23/23