Displaying Data from Multiple Tables (Join) Displaying Data from Multiple Tables (Join) Displaying Data from Multiple Tables (Join Displaying Data from Multiple Tables (Join Sub queries Sub queries Sub queries Sub queries Creating Sequences Creating Sequences Creating Sequences Creating Sequences Creating Views Creating Views Creating Views Creating Views Dynamic SQL Queries Dynamic SQL Queries Dynamic SQL Queries Dynamic SQL Queries Controlling User Access Controlling User Access Controlling User Access Controlling User Access Displaying Data from Multiple Tables (Join) Displaying Data from Multiple Tables (Join) Displaying Data from Multiple Tables (Join Displaying Data from Multiple Tables (Join Sub queries Sub queries Sub queries Sub queries Creating Sequences Creating Sequences Creating Sequences Creating Sequences Creating Views Creating Views Creating Views Creating Views Dynamic SQL Queries Dynamic SQL Queries Dynamic SQL Queries Dynamic SQL Queries Controlling User Access Controlling User Access Controlling User Access Controlling User Access CH3 Part2

Displaying Data from Multiple Tables (Join)

ObjectivesObjectives After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Write SELECT statements to access data from more than one table using equality and nonequality joins Write SELECT statements to access data from more than one table using equality and nonequality joins View data that generally does not meet a join condition by using outer joins View data that generally does not meet a join condition by using outer joins Join a table to itself Join a table to itself After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Write SELECT statements to access data from more than one table using equality and nonequality joins Write SELECT statements to access data from more than one table using equality and nonequality joins View data that generally does not meet a join condition by using outer joins View data that generally does not meet a join condition by using outer joins Join a table to itself Join a table to itself

EMPNO DEPTNO LOC NEW YORK CHICAGO NEW YORK DALLAS CHICAGO CHICAGO rows selected. EMPNO DEPTNO LOC NEW YORK CHICAGO NEW YORK DALLAS CHICAGO CHICAGO rows selected. Obtaining Data from Multiple Tables EMPDEPT EMPNOENAME...DEPTNO KING BLAKE MILLER DEPTNO DNAME LOC ACCOUNTINGNEW YORK 20RESEARCHDALLAS 30SALESCHICAGO 40OPERATIONSBOSTON

What Is a Join? Use a join to query data from more than one table. Use a join to query data from more than one table. Write the join condition in the WHERE clause. Write the join condition in the WHERE clause. Prefix the column name with the table name when the same column name appears in more than one table. Prefix the column name with the table name when the same column name appears in more than one table. Use a join to query data from more than one table. Use a join to query data from more than one table. Write the join condition in the WHERE clause. Write the join condition in the WHERE clause. Prefix the column name with the table name when the same column name appears in more than one table. Prefix the column name with the table name when the same column name appears in more than one table. SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2; SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2;

Cartesian Product A Cartesian product is formed when: A Cartesian product is formed when: A join condition is omitted A join condition is omitted A join condition is invalid A join condition is invalid All rows in the first table are joined to all rows in the second table All rows in the first table are joined to all rows in the second table To avoid a Cartesian product, always include a valid join condition in a WHERE clause. To avoid a Cartesian product, always include a valid join condition in a WHERE clause. A Cartesian product is formed when: A Cartesian product is formed when: A join condition is omitted A join condition is omitted A join condition is invalid A join condition is invalid All rows in the first table are joined to all rows in the second table All rows in the first table are joined to all rows in the second table To avoid a Cartesian product, always include a valid join condition in a WHERE clause. To avoid a Cartesian product, always include a valid join condition in a WHERE clause.

Generating a Cartesian Product ENAME DNAME KINGACCOUNTING BLAKE ACCOUNTING... KINGRESEARCH BLAKE RESEARCH rows selected. ENAME DNAME KINGACCOUNTING BLAKE ACCOUNTING... KINGRESEARCH BLAKE RESEARCH rows selected. EMP (14 rows) DEPT (4 rows) EMPNOENAME...DEPTNO KING BLAKE MILLER EMPNOENAME...DEPTNO KING BLAKE MILLER DEPTNO DNAME LOC ACCOUNTINGNEW YORK 20RESEARCHDALLAS 30SALESCHICAGO 40OPERATIONSBOSTON DEPTNO DNAME LOC ACCOUNTINGNEW YORK 20RESEARCHDALLAS 30SALESCHICAGO 40OPERATIONSBOSTON “Cartesian product: 14*4=56 rows”

Types of Joins Equijoin Non-equijoin Outer join Self join

What Is an Equijoin? EMP DEPT EMPNO ENAME DEPTNO KING BLAKE CLARK JONES MARTIN ALLEN TURNER JAMES WARD FORD SMITH rows selected. DEPTNO DNAME LOC ACCOUNTING NEW YORK 30 SALES CHICAGO 10 ACCOUNTINGNEW YORK 20 RESEARCHDALLAS 30 SALES CHICAGO 20 RESEARCHDALLAS rows selected. Foreign key Primary key

Retrieving Records with Equijoins SQL> SELECT emp.empno, emp.ename, emp.deptno, 2dept.deptno, dept.loc 3 FROM emp, dept 4 WHERE emp.deptno=dept.deptno; EMPNO ENAME DEPTNO DEPTNO LOC KING NEW YORK 7698 BLAKE CHICAGO 7782 CLARK NEW YORK 7566 JONES DALLAS rows selected.

Qualifying Ambiguous Column Names Use table prefixes to qualify column names that are in multiple tables. Use table prefixes to qualify column names that are in multiple tables. Improve performance by using table prefixes. Improve performance by using table prefixes. Distinguish columns that have identical names but reside in different tables by using column aliases. Distinguish columns that have identical names but reside in different tables by using column aliases. Use table prefixes to qualify column names that are in multiple tables. Use table prefixes to qualify column names that are in multiple tables. Improve performance by using table prefixes. Improve performance by using table prefixes. Distinguish columns that have identical names but reside in different tables by using column aliases. Distinguish columns that have identical names but reside in different tables by using column aliases.

Additional Search Conditions Using the AND Operator EMPDEPT EMPNO ENAME DEPTNO KING BLAKE CLARK JONES MARTIN ALLEN TURNER JAMES WARD FORD SMITH rows selected. DEPTNO DNAME LOC ACCOUNTINGNEW YORK 30SALES CHICAGO 10 ACCOUNTINGNEW YORK 20 RESEARCHDALLAS 30 SALES CHICAGO 20 RESEARCHDALLAS rows selected.

Using Table Aliases Simplify queries by using table aliases. Simplify queries by using table aliases. SQL> SELECT emp.empno, emp.ename, emp.deptno, 2 dept.deptno, dept.loc 3 FROM emp, dept 4 WHERE emp.deptno=dept.deptno; SQL> SELECT e.empno, e.ename, e.deptno, 2 d.deptno, d.loc 3 FROM emp e, dept d 4 WHERE e.deptno= d.deptno;

Joining More Than Two Tables NAMECUSTID JOCKSPORTS 100 TKB SPORT SHOP 101 VOLLYRITE 102 JUST TENNIS 103 K+T SPORTS 105 SHAPE UP 106 WOMENS SPORTS rows selected. NAMECUSTID JOCKSPORTS 100 TKB SPORT SHOP 101 VOLLYRITE 102 JUST TENNIS 103 K+T SPORTS 105 SHAPE UP 106 WOMENS SPORTS rows selected. CUSTOMER CUSTID ORDID rows selected. CUSTID ORDID rows selected.ORD ORDID ITEMID rows selected. ORDID ITEMID rows selected.ITEM

Non-EquijoinsNon-Equijoins EMPSALGRADE “salary in the EMP table is between low salary and high salary in the SALGRADE table” EMPNO ENAME SAL KING BLAKE CLARK JONES MARTIN ALLEN TURNER JAMES rows selected. GRADE LOSAL HISAL

Retrieving Records with Non-Equijoins ENAME SAL GRADE JAMES SMITH ADAMS rows selected. SQL> SELECT e.ename, e.sal, s.grade 2FROMemp e, salgrade s 3WHERE e.sal 4BETWEEN s.losal AND s.hisal;

Outer Joins EMP DEPT No employee in the OPERATIONS department ENAMEDEPTNO KING10 BLAKE30 CLARK10 JONES20... DEPTNO DNAME ACCOUNTING 30 SALES 10 ACCOUNTING 20RESEARCH... 40OPERATIONS

Outer Joins You use an outer join to also see rows that do not usually meet the join condition. You use an outer join to also see rows that do not usually meet the join condition. Outer join operator is the plus sign (+). Outer join operator is the plus sign (+). You use an outer join to also see rows that do not usually meet the join condition. You use an outer join to also see rows that do not usually meet the join condition. Outer join operator is the plus sign (+). Outer join operator is the plus sign (+). SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column(+) = table2.column; SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column(+) = table2.column; SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column = table2.column(+); SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column = table2.column(+);

Using Outer Joins SQL> SELECTe.ename, d.deptno, d.dname 2 FROMemp e, dept d 3 WHEREe.deptno(+) = d.deptno 4 ORDER BYe.deptno; ENAME DEPTNO DNAME KING 10 ACCOUNTING CLARK 10 ACCOUNTING OPERATIONS 15 rows selected.

Self Joins EMP (WORKER) EMP (MANAGER) “MGR in the WORKER table is equal to EMPNO in the MANAGER table” EMPNOENAME MGR KING 7698BLAKE CLARK JONES MARTIN ALLEN7698 EMPNOENAME KING 7698BLAKE

Joining a Table to Itself WORKER.ENAME||'WORKSFOR'||MANAG BLAKE works for KING CLARK works for KING JONES works for KING MARTIN works for BLAKE rows selected. WORKER.ENAME||'WORKSFOR'||MANAG BLAKE works for KING CLARK works for KING JONES works for KING MARTIN works for BLAKE rows selected. SQL> SELECT worker.ename||' works for '||manager.ename 2 FROM emp worker, emp manager 3 WHERE worker.mgr = manager.empno;

SummarySummary Equijoin Non-equijoin Outer join Self join SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2; SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2;

Sub queries

ObjectivesObjectives After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Describe the types of problems that subqueries can solve Describe the types of problems that subqueries can solve Define subqueries Define subqueries List the types of subqueries List the types of subqueries Write single-row and multiple-row subqueries Write single-row and multiple-row subqueries After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Describe the types of problems that subqueries can solve Describe the types of problems that subqueries can solve Define subqueries Define subqueries List the types of subqueries List the types of subqueries Write single-row and multiple-row subqueries Write single-row and multiple-row subqueries

Using a Subquery to Solve a Problem “Who has a salary greater than Jones’?” “Who has a salary greater than Jones’?” “Which employees have a salary greater than Jones’ salary?” Main Query ? “What is Jones’ salary?” ? Subquery

SubqueriesSubqueries The subquery (inner query) executes once before the main query. The subquery (inner query) executes once before the main query. The result of the subquery is used by the main query (outer query). The result of the subquery is used by the main query (outer query). The subquery (inner query) executes once before the main query. The subquery (inner query) executes once before the main query. The result of the subquery is used by the main query (outer query). The result of the subquery is used by the main query (outer query). SELECTselect_list FROMtable WHEREexpr operator (SELECTselect_list FROMtable);

2975 SQL> SELECT ename 2 FROM emp 3 WHERE sal > 4 (SELECT sal 5 FROM emp 6 WHERE empno=7566); Using a Subquery ENAME KING FORD SCOTT ENAME KING FORD SCOTT

Guidelines for Using Subqueries Enclose subqueries in parentheses. Enclose subqueries in parentheses. Place subqueries on the right side of the comparison operator. Place subqueries on the right side of the comparison operator. Do not add an ORDER BY clause to a subquery. Do not add an ORDER BY clause to a subquery. Use single-row operators with single-row subqueries. Use single-row operators with single-row subqueries. Use multiple-row operators with multiple-row subqueries. Use multiple-row operators with multiple-row subqueries. Enclose subqueries in parentheses. Enclose subqueries in parentheses. Place subqueries on the right side of the comparison operator. Place subqueries on the right side of the comparison operator. Do not add an ORDER BY clause to a subquery. Do not add an ORDER BY clause to a subquery. Use single-row operators with single-row subqueries. Use single-row operators with single-row subqueries. Use multiple-row operators with multiple-row subqueries. Use multiple-row operators with multiple-row subqueries.

Types of Subqueries Single-row subquery Single-row subquery Main query Subquery returns CLERK Multiple-row subquery CLERKMANAGER Main query Subquery returns Multiple-column subquery CLERK 7900 MANAGER 7698 Main query Subquery returns

Single-Row Subqueries Return only one row Return only one row Use single-row comparison operators Use single-row comparison operators Return only one row Return only one row Use single-row comparison operators Use single-row comparison operators Operator = > >= < <= <> Meaning Equal to Greater than Greater than or equal to Less than Less than or equal to Not equal to

Executing Single-Row Subqueries CLERK 1100 ENAME JOB MILLER CLERK ENAME JOB MILLER CLERK SQL> SELECT ename, job 2 FROM emp 3 WHERE job = 4(SELECT job 5 FROM emp 6 WHERE empno = 7369) 7 AND sal > 8(SELECT sal 9FROMemp 10WHEREempno = 7876);

Using Group Functions in a Subquery 800 ENAME JOB SAL SMITH CLERK 800 ENAME JOB SAL SMITH CLERK 800 SQL> SELECTename, job, sal 2 FROMemp 3 WHEREsal = 4(SELECTMIN(sal) 5FROMemp);

HAVING Clause with Subqueries The Oracle Server executes subqueries first. The Oracle Server executes subqueries first. The Oracle Server returns results into the HAVING clause of the main query. The Oracle Server returns results into the HAVING clause of the main query. The Oracle Server executes subqueries first. The Oracle Server executes subqueries first. The Oracle Server returns results into the HAVING clause of the main query. The Oracle Server returns results into the HAVING clause of the main query. 800 SQL> SELECTdeptno, MIN(sal) 2 FROMemp 3 GROUP BYdeptno 4 HAVINGMIN(sal) > 5(SELECTMIN(sal) 6FROMemp 7WHEREdeptno = 20);

What Is Wrong with This Statement? ERROR: ORA-01427: single-row subquery returns more than one row no rows selected ERROR: ORA-01427: single-row subquery returns more than one row no rows selected SQL> SELECT empno, ename 2 FROM emp 3 WHERE sal = 4(SELECT MIN(sal) 5FROM emp 6GROUP BY deptno); Single-row operator with multiple-row subquery

Will This Statement Work? no rows selected Subquery returns no values SQL> SELECT ename, job 2 FROM emp 3 WHERE job = 4(SELECTjob 5FROMemp 6WHEREename='SMYTHE');

Multiple-Row Subqueries Return more than one row Return more than one row Use multiple-row comparison operators Use multiple-row comparison operators Return more than one row Return more than one row Use multiple-row comparison operators Use multiple-row comparison operators Operator IN ANY ALL Meaning Equal to any member in the list Compare value to each value returned by the subquery Compare value to every value returned by the subquery

Using ANY Operator in Multiple-Row Subqueries EMPNO ENAME JOB MARTIN SALESMAN 7521 WARD SALESMAN EMPNO ENAME JOB MARTIN SALESMAN 7521 WARD SALESMAN SQL> SELECT empno, ename, job 2 FROM emp 3 WHERE sal < ANY 4(SELECTsal 5 FROMemp 6WHEREjob = 'CLERK') 7 AND job <> 'CLERK';

Using ALL Operator in Multiple-Row Subqueries EMPNO ENAME JOB KING PRESIDENT 7566 JONES MANAGER 7902 FORD ANALYST 7788 SCOTT ANALYST EMPNO ENAME JOB KING PRESIDENT 7566 JONES MANAGER 7902 FORD ANALYST 7788 SCOTT ANALYST SQL> SELECT empno, ename, job 2 FROM emp 3 WHERE sal > ALL 4 (SELECTavg(sal) 5 FROMemp 6GROUP BYdeptno);

SummarySummary Subqueries are useful when a query is based on unknown values. Subqueries are useful when a query is based on unknown values. SELECTselect_list FROMtable WHEREexpr operator (SELECT select_list FROM table);

Creating Sequences

What Is a Sequence? Automatically generates unique numbers Automatically generates unique numbers Is a sharable object Is a sharable object Is typically used to create a primary key value Is typically used to create a primary key value Replaces application code Replaces application code Speeds up the efficiency of accessing sequence values when cached in memory Speeds up the efficiency of accessing sequence values when cached in memory Automatically generates unique numbers Automatically generates unique numbers Is a sharable object Is a sharable object Is typically used to create a primary key value Is typically used to create a primary key value Replaces application code Replaces application code Speeds up the efficiency of accessing sequence values when cached in memory Speeds up the efficiency of accessing sequence values when cached in memory

The CREATE SEQUENCE Statement Define a sequence to generate sequential numbers automatically. Define a sequence to generate sequential numbers automatically. CREATE SEQUENCE sequence [INCREMENT BY n] [START WITH n] [{MAXVALUE n | NOMAXVALUE}] [{MINVALUE n | NOMINVALUE}] [{CYCLE | NOCYCLE}] [{CACHE n | NOCACHE}]; CREATE SEQUENCE sequence [INCREMENT BY n] [START WITH n] [{MAXVALUE n | NOMAXVALUE}] [{MINVALUE n | NOMINVALUE}] [{CYCLE | NOCYCLE}] [{CACHE n | NOCACHE}];

Creating a Sequence Create a sequence named DEPT_DEPTNO to be used for the primary key of the DEPT table. Create a sequence named DEPT_DEPTNO to be used for the primary key of the DEPT table. Do not use the CYCLE option. Do not use the CYCLE option. Create a sequence named DEPT_DEPTNO to be used for the primary key of the DEPT table. Create a sequence named DEPT_DEPTNO to be used for the primary key of the DEPT table. Do not use the CYCLE option. Do not use the CYCLE option. SQL> CREATE SEQUENCE dept_deptno 2 INCREMENT BY 1 3 START WITH 91 4 MAXVALUE NOCACHE 6 NOCYCLE; Sequence created. SQL> CREATE SEQUENCE dept_deptno 2 INCREMENT BY 1 3 START WITH 91 4 MAXVALUE NOCACHE 6 NOCYCLE; Sequence created.

Confirming Sequences Verify your sequence values in the USER_SEQUENCES data dictionary table. Verify your sequence values in the USER_SEQUENCES data dictionary table. The LAST_NUMBER column displays the next available sequence number. The LAST_NUMBER column displays the next available sequence number. Verify your sequence values in the USER_SEQUENCES data dictionary table. Verify your sequence values in the USER_SEQUENCES data dictionary table. The LAST_NUMBER column displays the next available sequence number. The LAST_NUMBER column displays the next available sequence number. SQL> SELECTsequence_name, min_value, max_value, 2 increment_by, last_number 3 FROMuser_sequences; SQL> SELECTsequence_name, min_value, max_value, 2 increment_by, last_number 3 FROMuser_sequences;

NEXTVAL and CURRVAL Pseudocolumns NEXTVAL returns the next available sequence value. NEXTVAL returns the next available sequence value. It returns a unique value every time it is referenced, even for different users. CURRVAL obtains the current sequence value. CURRVAL obtains the current sequence value. NEXTVAL must be issued for that sequence before CURRVAL contains a value. NEXTVAL returns the next available sequence value. NEXTVAL returns the next available sequence value. It returns a unique value every time it is referenced, even for different users. CURRVAL obtains the current sequence value. CURRVAL obtains the current sequence value. NEXTVAL must be issued for that sequence before CURRVAL contains a value.

NEXTVAL and CURRVAL Pseudocolumns NEXTVAL returns the next available sequence value. NEXTVAL returns the next available sequence value. It returns a unique value every time it is referenced, even for different users. CURRVAL obtains the current sequence value. CURRVAL obtains the current sequence value. NEXTVAL must be issued for that sequence before CURRVAL contains a value. NEXTVAL returns the next available sequence value. NEXTVAL returns the next available sequence value. It returns a unique value every time it is referenced, even for different users. CURRVAL obtains the current sequence value. CURRVAL obtains the current sequence value. NEXTVAL must be issued for that sequence before CURRVAL contains a value.

Using a Sequence Insert a new department named “MARKETING” in San Diego. Insert a new department named “MARKETING” in San Diego. View the current value for the DEPT_DEPTNO sequence. View the current value for the DEPT_DEPTNO sequence. Insert a new department named “MARKETING” in San Diego. Insert a new department named “MARKETING” in San Diego. View the current value for the DEPT_DEPTNO sequence. View the current value for the DEPT_DEPTNO sequence. SQL> INSERT INTOdept(deptno, dname, loc) 2 VALUES(dept_deptno.NEXTVAL, 3 'MARKETING', 'SAN DIEGO'); 1 row created. SQL> INSERT INTOdept(deptno, dname, loc) 2 VALUES(dept_deptno.NEXTVAL, 3 'MARKETING', 'SAN DIEGO'); 1 row created. SQL> SELECTdept_deptno.CURRVAL 2 FROMdual; SQL> SELECTdept_deptno.CURRVAL 2 FROMdual;

Using a Sequence Caching sequence values in memory allows faster access to those values. Caching sequence values in memory allows faster access to those values. Gaps in sequence values can occur when: Gaps in sequence values can occur when: A rollback occurs A rollback occurs The system crashes The system crashes A sequence is used in another table A sequence is used in another table View the next available sequence, if it was created with NOCACHE, by querying the USER_SEQUENCES table. View the next available sequence, if it was created with NOCACHE, by querying the USER_SEQUENCES table. Caching sequence values in memory allows faster access to those values. Caching sequence values in memory allows faster access to those values. Gaps in sequence values can occur when: Gaps in sequence values can occur when: A rollback occurs A rollback occurs The system crashes The system crashes A sequence is used in another table A sequence is used in another table View the next available sequence, if it was created with NOCACHE, by querying the USER_SEQUENCES table. View the next available sequence, if it was created with NOCACHE, by querying the USER_SEQUENCES table.

Modifying a Sequence Change the increment value, maximum value, minimum value, cycle option, or cache option. Change the increment value, maximum value, minimum value, cycle option, or cache option. SQL> ALTER SEQUENCE dept_deptno 2 INCREMENT BY 1 3 MAXVALUE NOCACHE 5 NOCYCLE; Sequence altered. SQL> ALTER SEQUENCE dept_deptno 2 INCREMENT BY 1 3 MAXVALUE NOCACHE 5 NOCYCLE; Sequence altered.

Guidelines for Modifying a Sequence You must be the owner or have the ALTER privilege for the sequence. You must be the owner or have the ALTER privilege for the sequence. Only future sequence numbers are affected. Only future sequence numbers are affected. The sequence must be dropped and re-created to restart the sequence at a different number. The sequence must be dropped and re-created to restart the sequence at a different number. You must be the owner or have the ALTER privilege for the sequence. You must be the owner or have the ALTER privilege for the sequence. Only future sequence numbers are affected. Only future sequence numbers are affected. The sequence must be dropped and re-created to restart the sequence at a different number. The sequence must be dropped and re-created to restart the sequence at a different number.

Removing a Sequence Remove a sequence from the data dictionary by using the DROP SEQUENCE statement. Remove a sequence from the data dictionary by using the DROP SEQUENCE statement. Once removed, the sequence can no longer be referenced. Once removed, the sequence can no longer be referenced. Remove a sequence from the data dictionary by using the DROP SEQUENCE statement. Remove a sequence from the data dictionary by using the DROP SEQUENCE statement. Once removed, the sequence can no longer be referenced. Once removed, the sequence can no longer be referenced. SQL> DROP SEQUENCE dept_deptno; Sequence dropped. SQL> DROP SEQUENCE dept_deptno; Sequence dropped.

Creating Views

What Is a View? EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO KING PRESIDENT 17-NOV BLAKE MANAGER MAY CLARK MANAGER JUN JONES MANAGER APR MARTIN SALESMAN SEP ALLEN SALESMAN FEB TURNER SALESMAN SEP JAMES CLERK DEC WARD SALESMAN FEB FORD ANALYST DEC SMITH CLERK DEC SCOTT ANALYST DEC ADAMS CLERK JAN MILLER CLERK JAN EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO KING PRESIDENT 17-NOV BLAKE MANAGER MAY CLARK MANAGER JUN JONES MANAGER APR MARTIN SALESMAN SEP ALLEN SALESMAN FEB TURNER SALESMAN SEP JAMES CLERK DEC WARD SALESMAN FEB FORD ANALYST DEC SMITH CLERK DEC SCOTT ANALYST DEC ADAMS CLERK JAN MILLER CLERK JAN EMP Table EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO KING PRESIDENT 17-NOV CLARK MANAGER JUN MILLER CLERK JAN JONES MANAGER APR SCOTT ANALYST DEC ADAMS CLERK JAN SMITH CLERK DEC FORD ANALYST DEC BLAKE MANAGER MAY MARTIN SALESMAN SEP ALLEN SALESMAN FEB TURNER SALESMAN SEP JAMES CLERK DEC WARD SALESMAN FEB EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO KING PRESIDENT 17-NOV CLARK MANAGER JUN MILLER CLERK JAN JONES MANAGER APR SCOTT ANALYST DEC ADAMS CLERK JAN SMITH CLERK DEC FORD ANALYST DEC BLAKE MANAGER MAY MARTIN SALESMAN SEP ALLEN SALESMAN FEB TURNER SALESMAN SEP JAMES CLERK DEC WARD SALESMAN FEB EMPNO ENAME JOB KING PRESIDENT 7782 CLARK MANAGER 7934 MILLER CLERK EMPVU10 View EMPVU10 View

Why Use Views? To restrict data access To restrict data access To make complex queries easy To make complex queries easy To allow data independence To allow data independence To present different views of the same data To present different views of the same data To restrict data access To restrict data access To make complex queries easy To make complex queries easy To allow data independence To allow data independence To present different views of the same data To present different views of the same data

Simple Views and Complex Views FeatureSimple ViewsComplex Views Number of tablesOneOne or more Contain functionsNoYes Contain groups of dataNoYes DML through viewYesNot always

Creating a View You embed a subquery within the CREATE VIEW statement. You embed a subquery within the CREATE VIEW statement. The subquery can contain complex SELECT syntax. The subquery can contain complex SELECT syntax. The subquery cannot contain an ORDER BY clause. The subquery cannot contain an ORDER BY clause. You embed a subquery within the CREATE VIEW statement. You embed a subquery within the CREATE VIEW statement. The subquery can contain complex SELECT syntax. The subquery can contain complex SELECT syntax. The subquery cannot contain an ORDER BY clause. The subquery cannot contain an ORDER BY clause. CREATE [OR REPLACE] VIEW view_name AS subquery; CREATE [OR REPLACE] VIEW view_name AS subquery;

Creating a View Create a view, EMPVU10, that contains details of employees in department 10. Create a view, EMPVU10, that contains details of employees in department 10. Describe the structure of the view by using the SQL*Plus DESCRIBE command. SQL> DESCRIBE empvu10 SQL> CREATE VIEW empvu10 2 AS SELECTempno, ename, job 3 FROMemp 4 WHEREdeptno = 10; View created.

Creating a View Create a view by using column aliases in the subquery. Create a view by using column aliases in the subquery. Select the columns from this view by the given alias names. Select the columns from this view by the given alias names. Create a view by using column aliases in the subquery. Create a view by using column aliases in the subquery. Select the columns from this view by the given alias names. Select the columns from this view by the given alias names. SQL> CREATE VIEW salvu30 2 AS SELECTempno EMPLOYEE_NUMBER, ename NAME, 3sal SALARY 4 FROMemp 5 WHEREdeptno = 30; View created.