ITEC212 Database Management Systems Laboratory 2

Transcription

1 ITEC212 Database Management Systems Laboratory 2 Aim: To learn how to use Single Row Functions and other important functions. In this handout we will learn about the single row functions that are used on a single row at a time. These functions are very useful and are used very often in the select and where clause of the select statement and also in the insert and delete commands of SQL as well as the PL/SQL procedures. Below is a list of some of the single row functions that are used more frequently. CHARACTER FUNCTIONS LOWER(column expression) Converts each letter to lowercase. UPPER(column expression) Converts each letter to uppercase. INITCAP(column expression) First character of each word is converted to uppercase and the rest to lowercase. CONCAT(column1 expression1,column2 expression2) Concatenates (joins) the first column or expression to the second one. Equivalent to the concatenate operator ( ). SUBSTR(column expression,m[,n]) Returns the specified n characters from position m of the column or expression. If n is not specified all characters from mth position until the end of the string are returned. LENGTH(column expression) Returns the number of characters in the column or expression. NVL(column1 expression1, value) Returns the first value if it is NOT NULL and the second value if the first one is NULL. NVL2(column1 expression1, notnullvalue, nullvalue) Checks for null as well as not null values. If the column has a not null value, the second parameter is displayed. If the column has a null value, the third parameter is displayed. RTRIM(column expr,c) Removes the blanks on the right hand side. LTRIM(column expr,c) Removes the blanks on the left hand side. Example 1: a) Display the job followed by name of each employee in department 30. The job should be in all lower case and the name should be in initial capitalization. SQL> SELECT LOWER(JOB_ID), INITCAP(LAST_NAME),DEPARTMENT_ID b) Display the job and name as a single column called EMPLOYEES. The job should be in all lower case, the name should be in initial capitalization and department should be in all upper case, SQL> SELECT UPPER(JOB_ID) ' ' INITCAP(LAST_NAME) EMPLOYEES,UPPER(DEPARTMENT_ID) Example 2: Display all information on all employees whose name contains the substring 'LA' starting from the second position. SQL> SELECT LAST_NAME WHERE SUBSTR(LAST_NAME,2,2) = 'LA';

2 DUAL table: The DUAL table is a special one-row, one-column table present by default in Oracle and other database installations. In Oracle, the table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'. It is suitable for use in selecting a pseudo column such as SYSDATE or USER. Dual table can be also used to display the outcome of any character and number functions or an arithmetic expression. NUMBER FUNCTIONS ROUND(column expression,n) Rounds the column or expression to n decimal places. If n is omitted it is assumed to be 0. If n is negative numbers to the left of the decimal points are rounded. TRUNC(column expression,n) Truncates the column or expression to n decimal places. If n is omitted it is assumed to be 0. If n is negative numbers to the left of the decimal points are truncated to zero. MOD(m,n) Returns remainder of m divided by n. Example 3: SQL> SELECT ROUND( ,-1), ROUND( ,0), ROUND( ,2) FROM DUAL; ROUND ( ,-1) ROUND( ,0) ROUND( ,2) Example 4: SQL> SELECT TRUNC( ,3), TRUNC( ,0), TRUNC( ,-1) FROM DUAL; TRUNC( ,3) TRUNC( ,0) TRUNC( ,-1) Database stores dates as numbers therefore some arithmetic operations are allowed on dates. A date value contains the time values as well therefore you can find out the exact time an operation took place. OPERATION RESULT DESCRIPTION DATE + NUMBER : Date Adds a number of days to a date. DATE - NUMBER : Date Subtracts a number of days from a date. DATE1 - DATE2 : Number of days (Subtracts one date from another date) DATE + NUMBER / 24 Date Adds a number of hours to a date Example 5: Find the name and number of years each employee has been employed for. SQL> SELECT LAST_NAME, ROUND((SYSDATE-HIRE_DATE)/365) ; Example 6: Find the name and number of days each employee has been employed. SQL> SELECT LAST_NAME, (SYSDATE-HIRE_DATE) ;

3 Example 7: Find the name, number of days and number of weeks each employee has been employed. Department number should be 30 and employee name should be initial capitalization. SQL> SELECT INITCAP(LAST_NAME), (SYSDATE-HIRE_DATE) NUMBER OF DAYS, (SYSDATE- HIRE_DATE)/7 NUMBER OF WEEKS DATE FUNCTIONS SYSDATE: Returns the current date and time in a DATE datatype. CURRENT_DATE: Returns the current date and time in a DATE datatype. CURRENT_TIMESTAMP: Returns the current date and time in a TIMESTAMP datatype. MONTHS_BETWEEN(date1,date2): Finds the number of months between date1 and date2. The result is negative if date1 is before date2. ADD_MONTHS(date,n) : Adds n number of months to the month field of the date. NEXT_DAY(date,'char') : Finds the date of next day of the week that is represented by 'char' (ex: Monday) LAST_DAY(date) : Finds the date of the last day of the month that contains the date. EXTRACT: Returns component of a date/time expression. (ex: select extract(day from sysdate) from dual); ROUND(date [, 'fmt' ]) : Rounds a date to a format model specified by fmt (format). Fmt can be year or months etc. If fmt is not specified the date is set to midnight and returns the date. TRUNC(date [, 'fmt' ]) : If fmt is YEAR it returns the date of the first day of the year containing this date. If fmt is not specified, it finds the date of first day of the month containing the date. Example 8: Find the hiredate, last day of months and the date of the next Friday after the hiredate for all employees who work for department number 30. SQL> SELECT HIRE_DATE, LAST_DAY(HIRE_DATE), NEXT_DAY(HIRE_DATE,'FRIDAY') Example 9: SQL> SELECT ROUND(HIRE_DATE,'MONTH), ROUND(HIRE_DATE,'YEAR'), ROUND(HIRE_DATE,'DAY') WHERE LAST_NAME='KING'; ROUND(HIREDATE,'MONTH) ROUND(HIREDATE,'YEAR') ROUND(HIREDATE,'DAY') 01-DEC JAN NOV-81 CONVERTION FUNCTIONS TO_CHAR(number date [, 'fmt' ]) Converts a nuimber of date to a varchar2 character string with format fmt. TO_NUMBER(char) Converts a character string containing digits to number TO_DATE(char [, 'fmt' ]) Converts a character string representing a date value according to the fmt specified. If fmt is omitted, format is DD-MON-YY

4 SOME VALID DATE FORMATS YYYY,YYY,YY,Y: Four-digit year. Last 3,2,1 digits in the year. YEAR: Year spelled out. MM: 2 digit representation of MONTH. MONTH: Month name spelled out. MON: Month name abbreviated. DDD,DD,D: Day of year, month week. DAY: Day of week spelled out. DY: Day of week abbreviated. FM: Returns value with no leading or trailing blanks. Ex: SQL> select to_char(sysdate, 'DAY') 2 from dual; TO_CHAR(SYSDATE,'DAY') FRIDAY SQL> select length(to_char(sysdate, 'DAY')),length(to_char(sysdate, 'fmday')) 2 from dual LENGTH(TO_CHAR(SYSDATE,'DAY')) LENGTH(TO_CHAR(SYSDATE,'FMDAY')) (BLANKS REMOVED) SUFFIXES FOR DISPLAYING NUMBERS TH Ordinal number (DDTH for 5th) SP Spelled out number (DDSP for FIFTH) Example 10: Display the hiredate of KING with everything spelled out. SQL> SELECT LAST_NAME, TO_CHAR(HIREDATE,.'FMDAY' "of" DDSP MONTH YEAR') WHERE UPPER(LAST_NAME)='KING'; ENAME HIREDATE KING TUESDAY of SEVENTEENTH NOVEMBER NINETEEN EIGHTYONE Exercises: 1. Display the concatenation of employees last name and salary (separated by comma) under the column heading "EMPLOYEES AND THEIR SALARIES ". 2. Display the last name, hiredate, salary and salary increased by 10% for each employee. Label the new column NEW SALARY. 3. Display the full name, salary and add a column that subtracts the old salary from the new salary. Label the column INCREASE. 4. Display the first name and last name of employees whose first name contain N in the last second character. 5. For each employee, display the employee s last name and calculate the number of months between today and the date the employee was hired. Label the column MONTHS_WORKED. Order your results by the number of months employed. Round the number of months up to the closest whole number.

5 6. Display the first name and salary of all employees in the following format: <employee_name> earns $<employee_salary> but wants $<3* employee_salary> Label the column Dream Salaries. 7. Display each employee s last name, hire date and salary review date, which is the first Monday after six months of service. Label the column REVIEW. Format the dates to appear in the format similar to Monday, the Thirty-First of October, Display the last name, hire date, and day of the week on which the employee started. Label the column DAY. Order the results by the week starting with Monday. 9. Find the date 30 days from now. 10. Write a query that displays the employees last names and commission amounts. If an employee does not earn commission, put No Commission. Label the column COMM. 11. Display first name and last name of employees who were hired in the month of MAY. Display the date in the following format: 31 st of OCT 2016, Monday 12. Display first name, last name and department id of employees who were hired after the 100th day of the year. 13. Display first name and last name of employees who were hired before Find the date of next Monday after 3 months from now. 15. What is the last day of the current month?