Writing Basic SQL Statements. Select functions презентация

Writing Basic SQL Statements

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 SQL*Plus commands

Capabilities of SQL SELECT Statements

Basic SELECT Statement SELECT identifies what columns FROM identifies which table

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. Tabs and indents are used to enhance readability.

Selecting All Columns

Selecting Specific Columns

Column Heading Defaults Default justification Left: Date and character data Right: Numeric data Default display: Uppercase

Arithmetic Expressions Create expressions on NUMBER and DATE data by using arithmetic operators.

Using Arithmetic Operators

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

Using Parentheses

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.

Null Values in Arithmetic Expressions Arithmetic expressions containing a null value evaluate to null.

Defining a Column Alias Renames a column heading Is useful with calculations Immediately follows column name; optional AS keyword between column name and alias Requires double quotation marks if it contains spaces or special characters or is case sensitive

Using Column Aliases

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

Literal Character Strings A literal is a character, expression, or number 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

Duplicate Rows The default display of queries is all rows, including duplicate rows.

Eliminating Duplicate Rows

SQL and SQL*Plus Interaction

SQL Statements Versus SQL*Plus Commands

Overview of SQL*Plus Log in to SQL*Plus. Describe the table structure. Edit your SQL statement. Execute SQL from SQL*Plus. Save SQL statements to files and append SQL statements to files. Execute saved files. Load commands from file to buffer to edit.

Logging In to SQL*Plus From Windows environment: From command line: sqlplus [username[/password [@database]]]

Displaying Table Structure Use the SQL*Plus DESCRIBE command to display the structure of a table.

Displaying Table Structure

SQL*Plus Editing Commands A[PPEND] text C[HANGE] / old / new C[HANGE] / text / CL[EAR] BUFF[ER] DEL DEL n DEL m n

SQL*Plus Editing Commands I[NPUT] I[NPUT] text L[IST] L[IST] n L[IST] m n R[UN] n n text 0 text

SQL*Plus File Commands SAVE filename GET filename START filename @ filename EDIT filename SPOOL filename

Summary Use SQL*Plus as an environment to: Execute SQL statements Edit SQL statements

Practice Overview Selecting all data from different tables Describing the structure of tables Performing arithmetic calculations and specifying column names Using SQL*Plus editor