What are temporary tables? When are they useful?

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Esmond Leo Gibbs
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1 What are temporary tables? When are they useful? Temporary tables exists solely for a particular session, or whose data persists for the duration of the transaction. The temporary tables are generally used to support specialized rollups or specific application processing requirements. Unlike a permanent table, a space is not allocated to a temporary table when it is created. Space will be dynamically allocated for the table as rows are inserted. The CREATE GLOBAL TEMPORARY TABLE command is used to create a temporary table in Oracle.

2 Syntax of TEMPORARY TABLE command CREATE GLOBAL TEMPORARY TABLE <table_name> (<columns details> ) ON COMMIT {PRESERVE DELETE} ROWS;

3 External tables External tables allow Oracle to query data that is stored outside the database in flat files. The ORACLE_LOADER driver can be used to access any data stored in any format that can be loaded by SQL*Loader. Create the external table using the CREATE TABLE..ORGANIZATION EXTERNAL syntax.

4 External tables Create a directory object pointing to the location of the files. create or replace directory <directory name> as 'd:\';

5 External table create directory dn as 'd:\'; Create database table and insert data into it create table tt1(c1 int); insert into tt1 values(101); Create external table create table exttable (c) organization external (type ORACLE_DATAPUMP default directory dn location('exttab.dat'))as select c1 from tt1; Query to external table select * from exttable;

6 Querying Data From Flat Files in Oracle CREATE OR REPLACE DIRECTORY ext_tab_data AS 'E:/data'; CREATE TABLE countries_ext ( country_code VARCHAR2(5), country_name VARCHAR2(50), country_language VARCHAR2(50) ) ORGANIZATION EXTERNAL ( TYPE ORACLE_LOADER DEFAULT DIRECTORY ext_tab_data ACCESS PARAMETERS ( RECORDS DELIMITED BY NEWLINE FIELDS TERMINATED BY ',' MISSING FIELD VALUES ARE NULL ( country_code CHAR(5), country_name CHAR(50), country_language CHAR(50) ) ) LOCATION ('Countries1.txt','Countries2.txt') ) PARALLEL 5 REJECT LIMIT UNLIMITED;

7 Create a table using a subquery Create table <new table name> as select <colname1>, <colname2>. From <existing table name> CREATE TABLE dept80 AS SELECT empolyee_id,last_name, salary*12, hire date FROM employess WHERE department_id=80

8 The Human Resource(HR) Schema

9 The Human Resource(HR) Schema

10 ANY operator The ANY comparison condition is used to compare a value to a list or subquery. It must be preceded by =,!=, >, <, <=, >= and followed by a list or subquery. SELECT empno, sal FROM emp WHERE sal > ANY (2000, 3000, 4000); -- Transformed to equivalent statement without ANY. SELECT empno, sal FROM emp WHERE sal > 2000 OR sal > 3000 OR sal > 4000;

11 ALL operator The ALL comparison condition is used to compare a value to a list or subquery. It must be preceded by =,!=, >, <, <=, >= and followed by a list or subquery. SELECT empno, sal FROM emp WHERE sal > ALL (2000, 3000, 4000); -- Transformed to equivalent statement without ALL. SELECT empno, sal FROM emp WHERE sal > 2000 AND sal > 3000 AND sal > 4000;

12 Oracle Built in Functions There are two types of functions in Oracle. 1) Single Row Functions: Single row or Scalar functions return a value for every row that is processed in a query. 2) Group Functions: These functions group the rows of data based on the values returned by the query. The group functions are used to calculate aggregate values like total or average, which return just one total or one average value after processing a group of rows.

13 There are four types of single row functions. They are: 1) Numeric Functions: These are functions that accept numeric input and return numeric values. 2) Character or Text Functions: These are functions that accept character input and can return both character and number values. 3) Date Functions: These are functions that take values that are of datatype DATE as input and return values of datatype DATE, except for the MONTHS_BETWEEN function, which returns a number. 4) Conversion Functions: These are functions that help us to convert a value in one form to another form. For Example: a null value into an actual value, or a value from one datatype to another datatype like TO_CHAR, TO_NUMBER, TO_DATE etc. You can combine more than one function together in an expression. This is known as nesting of functions.

14 What is a DUAL Table in Oracle? This is a single row and single column dummy table provided by oracle. This is used to perform mathematical calculations without using a table. Select * from DUAL

15 Numeric Functions: Numeric functions are used to perform operations on numbers. They accept numeric values as input and return numeric values as output. Few of the Numeric functions are: Function Name Examples Return Value ABS (x) CEIL (x) FLOOR (x) TRUNC (x, y) ROUND (x, y) ABS (1) ABS (-1) CEIL (2.83) CEIL (2.49) CEIL (-1.6) FLOOR (2.83) FLOOR (2.49) FLOOR (-1.6) ROUND ( , 1) ROUND ( , 0) ROUND ( , - 1) TRUNC ( , 2) TRUNC (-54, 1) TRUNC (5.7) TRUNC (142, -1)

16 Character or Text Functions: Character or text functions are used to manipulate text strings. They accept strings or characters as input and can return both character and number values as output. Function Name Examples Return Value LOWER(string_value) LOWER('Good Morning') good morning UPPER(string_value) UPPER('Good Morning') GOOD MORNING INITCAP(string_value) INITCAP('GOOD MORNING') Good Morning LTRIM(string_value, trim_text) LTRIM ('Good Morning', 'Good) Morning RTRIM (string_value, trim_text) RTRIM ('Good Morning', ' Morning') Good TRIM (trim_text FROM string_value) TRIM ('o' FROM 'Good Morning') Gd Mrning SUBSTR (string_value, m, n) SUBSTR ('Good Morning', 6, 7) Morning LENGTH (string_value) LENGTH ('Good Morning') 12 LPAD (string_value, n, pad_value) LPAD ('Good', 6, '*') **Good RPAD (string_value, n, pad_value) RPAD ('Good', 6, '*') Good**

17 Date Functions: These are functions that take values that are of datatype DATE as input and return values of datatypes DATE, except for the MONTHS_BETWEEN function, which returns a number as output. Function Name Examples Return Value ADD_MONTHS ( ) MONTHS_BETW EEN( ) NEXT_DAY( ) LAST_DAY( ) ADD_MONTHS ('16-Sep-81', 3) MONTHS_BETWEE N ('16-Sep-81', '16-Dec-81') NEXT_DAY ('01- Jun-08', 'Wednesday') LAST_DAY ('01- Jun-08') 16-Dec JUN Jun-08 NEW_TIME( ) NEW_TIME ('01- Jun-08', 'IST', 'EST') 31-May-08

18 Conversion Functions: These are functions that help us to convert a value in one form to another form. For Ex: a null value into an actual value, or a value from one datatype to another datatype like NVL, TO_CHAR, TO_NUMBER, TO_DATE. Few of the conversion functions available in oracle are: Function Name TO_CHAR (x [,y]) TO_DATE (x [, date_format ]) NVL (x, y) Return Value Converts Numeric and Date values to a character string value. It cannot be used for calculations since it is a string value. Converts a valid Numeric and Character values to a Date value. Date is formatted to the format specified by 'date_format'. If 'x' is NULL, replace it with 'y'. 'x'and 'y' must be of the same datatype.

19 Function Name Examples Return Value TO_CHAR () TO_CHAR (3000, '$9999') TO_CHAR (SYSDATE, 'Day, Month YYYY') $3000 Monday, June 2008 TO_DATE () TO_DATE ('01-Jun- 08') 01-Jun-08 NVL () NVL (null, 1) 1

20 Examples select TO_CHAR (30, '$99') from dual; select TO_DATE (SYSDATE) from dual; SELECT TO_CHAR (SYSDATE, 'Day, Month YYYY') from dual

21 INTERSECT operator The SQL INTERSECT operator is used to return the results of 2 or more SELECT statements. However, it only returns the rows selected by all queries or data sets. If a record exists in one query and not in the other, it will be omitted from the INTERSECT results. SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions] INTERSECT SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions];

22 UNION ALL Operator The SQL UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It does not remove duplicate rows between the various SELECT statements (all rows are returned). Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types. What is the difference between UNION and UNION ALL? UNION removes duplicate rows. UNION ALL does not remove duplicate rows.

23 Syntax SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions] UNION ALL SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions];

24 MINUS operator The SQL MINUS operator is used to return all rows in the first SELECT statement that are not returned by the second SELECT statement. Each SELECT statement will define a dataset. The MINUS operator will retrieve all records from the first dataset and then remove from the results all records from the second dataset. SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions] MINUS SELECT expression1, expression2,... expression_n FROM tables [WHERE conditions];

25 EXISTS Condition with the SELECT Statement The SQL EXISTS condition is used in combination with a subquery and is considered to be met, if the subquery returns at least one row. It can be used in a SELECT, INSERT, UPDATE, or DELETE statement. SELECT * FROM emp WHERE EXISTS (SELECT * FROM dept WHERE emp.ecode = dept.eno);

26 IF THEN ELSE logic in a SELECT statement SELECT ename, CASE WHEN sal = 1000 THEN 'Minimum wage' WHEN sal > 1000 THEN 'Over paid' ELSE 'Under paid' END AS "Salary Status" FROM emp; SELECT ename, esal, CASE WHEN esal = THEN 'Minimum wage' WHEN esal > THEN 'Over paid' ELSE 'Under paid' END AS "Salary Status" FROM emp;

27 Display names of all constraints for a table in Oracle SQL select constraint_name,constraint_type from user_constraints where table_name = 'DEPT'; R = Referential Constraint/Foreign Key constraint C = Check Constraint P = Primary Key U = Unique Key select * from user_constraints where table_name='k12'

28 On Delete Cascade Option create table k2 ( rno int references k1(rno) on delete cascade, dname int); drop table k1 cascade constraint; To drop Foreign Key alter table k12 drop constraint SYS_C ;

29 To add On delete cascade Drop foreign key first then alter table k12 modify foreign key (rno) references k11 (rno) on delete cascade;

UNIT III INTRODUCTION TO STRUCTURED QUERY LANGUAGE (SQL)

UNIT III INTRODUCTION TO STRUCTURED QUERY LANGUAGE (SQL) 3.1Data types 3.2Database language. Data Definition Language: CREATE,ALTER,TRUNCATE, DROP 3.3 Database language. Data Manipulation Language: INSERT,SELECT,UPDATE,DELETE