Les01-Oracle

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 Selection Projection Table 1 Table 2 Table 1 Table 1 Join

Basic SELECT Statement SELECT identifies what columns. FROM identifies which table. SELECT [DISTINCT] {*, column [ alias ],...} FROM 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 DEPTNO DNAME LOC --------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON SQL> SELECT * 2 FROM dept;

Selecting Specific Columns DEPTNO LOC --------- ------------- 10 NEW YORK 20 DALLAS 30 CHICAGO 40 BOSTON SQL> SELECT deptno, loc 2 FROM dept;

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. Operator + - * / Description Add Subtract Multiply Divide

Using Arithmetic Operators SQL> SELECT ename, sal, sal+300 2 FROM emp; ENAME SAL SAL+300 ---------- --------- --------- KING 5000 5300 BLAKE 2850 3150 CLARK 2450 2750 JONES 2975 3275 MARTIN 1250 1550 ALLEN 1600 1900 ... 14 rows selected.

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 SQL> SELECT ename, sal, 12*sal+100 2 FROM emp; ENAME SAL 12*SAL+100 ---------- --------- ---------- KING 5000 60100 BLAKE 2850 34300 CLARK 2450 29500 JONES 2975 35800 MARTIN 1250 15100 ALLEN 1600 19300 ... 14 rows selected.

Using Parentheses SQL> SELECT ename, sal, 12*(sal+100) 2 FROM emp; ENAME SAL 12*(SAL+100) ---------- --------- ----------- KING 5000 61200 BLAKE 2850 35400 CLARK 2450 30600 JONES 2975 36900 MARTIN 1250 16200 ... 14 rows selected.

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. SQL> SELECT ename, job, comm 2 FROM emp; ENAME JOB COMM ---------- --------- --------- KING PRESIDENT BLAKE MANAGER ... TURNER SALESMAN 0 ... 14 rows selected.

Null Values in Arithmetic Expressions Arithmetic expressions containing a null value evaluate to null. SQL> select ename, 12*sal+comm 2 from emp 3 WHERE ename='KING'; ENAME 12*SAL+COMM ---------- ----------- KING

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 SQL> SELECT ename AS name, sal salary 2 FROM emp; NAME SALARY ------------- --------- ... SQL> SELECT ename "Name", 2 sal*12 "Annual Salary" 3 FROM emp; Name Annual Salary ------------- ------------- ...

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 SQL> SELECT ename||job AS "Employees" 2 FROM emp; Employees ------------------- KINGPRESIDENT BLAKEMANAGER CLARKMANAGER JONESMANAGER MARTINSALESMAN ALLENSALESMAN ... 14 rows selected.

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 Employee Details ------------------------- KING is a PRESIDENT BLAKE is a MANAGER CLARK is a MANAGER JONES is a MANAGER MARTIN is a SALESMAN ... 14 rows selected. SQL> SELECT ename ||' '||'is a'||' '||job 2 AS "Employee Details" 3 FROM emp;

Duplicate Rows The default display of queries is all rows, including duplicate rows. SQL> SELECT deptno 2 FROM emp; DEPTNO --------- 10 30 10 20 ... 14 rows selected.

Eliminating Duplicate Rows Eliminate duplicate rows by using the DISTINCT keyword in the SELECT clause. SQL> SELECT DISTINCT deptno 2 FROM emp; DEPTNO --------- 10 20 30

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

Displaying Table Structure SQL> DESCRIBE dept Name Null? Type ----------------- -------- ------------ DEPTNO NOT NULL NUMBER(2) DNAME VARCHAR2(14) LOC VARCHAR2(13)

Summary Use SQL*Plus as an environment to: Execute SQL statements Edit SQL statements SELECT [DISTINCT] {*, column [ alias ],...} FROM table;

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

Les01-Oracle

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