Functions and string manipulation Lab 2 Week 2

Date functions Commonly used date functions are: –sysdate –next_day –add_months –last_day –months_between –least –greatest –round –trunc

Date functions and the DUAL table. Current date and time: SQL> select sysdate from dual; SYSDATE SEP-05 Dual: – This supplies values for system variables. Current date and time is one of them. We will come across more later.

Sample date functions SQL> select 2 order_date as "Date", 3 to_char(order_date,'DAY'), 4 next_day(order_date,'MONDAY') as "Monday following", 5 last_day(order_date) as "Last day of month", 6 add_months (order_date,3) as "3 months later" 7 from corder;

Meaning… To_char(date,format) –Converts the date to the specified format. Next_day(date,dayofweek) –Gives the date of the next ‘dayofweek’ after the date given. Last_day(date) –Gives the last day of the month in the date specified. add_months (date,int) –Adds int months to the given date.

Produces… Date TO_CHAR(O Monday fo Last day 3 months FEB-02 SATURDAY 04-FEB FEB MAY FEB-05 FRIDAY 07-FEB FEB MAY FEB-05 SUNDAY 07-FEB FEB MAY FEB-05 THURSDAY 14-FEB FEB MAY FEB-05 SATURDAY 14-FEB FEB MAY FEB-05 FRIDAY 21-FEB FEB MAY FEB-05 TUESDAY 28-FEB FEB MAY FEB-05 SATURDAY 14-FEB FEB MAY rows selected.

Date functions Sysdate gives current date Next_day(d,day) where d is a date and day is a string representing a day of the week. –E.g. next_day(’14-dec-2005’,’Monday’) will return ’19-dec-2005’ Add_months(d,count) adds n months to d. Last_day(d) returns the date corresponding to the last day of the month in which d belongs. Months_between(d1,d2) Least(d1,d2,…,dn) Greatest(d1,…,dn) Trunc(d) returns the date (d) with the time at midnight.

Functions in SQL There are many types of functions provided. The ones that are used most are: –Date and Time functions –Mathematical functions –String functions There follows a list of all functions in these categories. We will practice only the most popularly used.

All about dates Dates are relative – i.e. the date and time are the same function. The current date and time depends on where you are in the world. The date format '12-dec-2005' will work, but NOT ’12-dec-2005’. –The apostrophes, or quotes, are different. Microsoft Word / PowerPoint will automatically change from ' to ‘.

Formatting the date To_char(d,format) returns the date in the format specified: –Mm returns month number –Mon returns the month in 3-character format –D returns the day number in the week –DD returns the day number in the month –DDD returns the day number in the year –DY gives the weekday in 3-character format –DAY gives the weekday name –Y returns the last digit of the year –Yy returns the last 2 digits of the year –Yyyy returns the 4-digit year –Hh12 returns the hours of the day(1 -12) –Hh24 returns the hours of the day (1 – 24) –Mi returns the minutes of the hour –Ss returns the seconds of the minute –AM returns AM or PM

resources These sites are helpful: – –

To put a name on a column Use the ‘as’ clause to give a name to a column. –Unitprice as Price or –UnitPrice as “Unit Price” –Note double quotes. This can be used on any column, but is especially useful in a derived column. New columns can be derived from existing fields: E.g. the value of an item in stock is the number in stock by the unit price. Surround the alias with double quotes: SQL> select stock_description as "Name" from stock; Name Brick - red, 30x100 Cavity blocks(100) 2"x4" lengths 6" Nails(50) 6" Nails(100) Workbench cordless Drill Cavity blocks(500) Cavity blocks(200) 9 rows selected. SQL>

Naming sample SQL> select 2 stock_description as "Name", 3 QuantityRequired as "Quantity", 4 Unit_Price as "at Price", 5 Unit_Price * QuantityRequired as "SubTotal" 6 from Stock join Corderline on 7 stock.stock_code = corderline.stock_code; Name Quantity at Price SubTotal Brick - red, 30x

String functions - Concatenation Concatenation: SQL> select supplier_name||','||supplier_address from supplier; SUPPLIER_NAME||','||SUPPLIER_ADDRESS Buckleys,Quarry town, Quarrysville, D44. Brendan Moore,44 Kevin St., D8 James McGovern,33 Synge St. Liam Keenan,33 Mount Vernon Ave Mary O'Brien,Appian Way, D2 Oliver Moore,Georges St., D2 June Browne,33 Liberty Lane Paul Sloan,44 Liberty Lane Kevin Kelly,33 Bride St, D8 Robert O'Mahony,Fitzwilliam Sq Patricia O'Brien,21 Liberty Lane, D8 11 rows selected.

String manipulation Concatenation: use || instead of, Pad out a string (from the left) to a specified length: –Lpad(string,length,’padding char’) –Rpad does the same, but pads from the right. Trim strings of characters uses –Ltrim(string,’trim char’) –Rtrim trims from the right.

Example of lpad SQL> select lpad(stock_code,12,'x') as "stock code", stock_description from stock; stock code STOCK_DESCRIPTION xxxxxxxxA111 Red bricks(100) xxxxxxxBRK11 Brick - red, 30x100 xxxxxxxxA101 Cavity blocks(100) xxxxxxxxB101 2"x4" lengths xxxxxxxxB111 Window Frames 2'x4' xxxxxxxxC101 6" Nails(50) xxxxxxxxC121 6" Nails(100) xxxxxxxxD101 Workbench xxxxxxxxD131 cordless Drill xxxxxxxxE101 Cavity blocks(500) xxxxxxxxE141 Cavity blocks(200) 11 rows selected.

Trim from the right SQL> select stock_code, rtrim(stock_code,'1') from stock; STOCK RTRIM A101 A10 A111 A B101 B10 B111 B BRK11 BRK C101 C10 C121 C12 D101 D10 D131 D13 E101 E10 E141 E14 11 rows selected.

Look up… Lower(string) Upper(string) Length(string) Substr(string,start,[n]) Instr(string,’chars’[,start [,n]])

Exercises Retrieve the system date and display it in 5 different formats. To demonstrate the effectiveness of ‘order by’: –Select all from the builder’s sorderline table –Select all from the builder’s sorderline table in order of the quantity of stock that is required. –Select all from the builder’s sorderline table in descending order of the quantity of stock that is required.

More exercises Show the order id, the customer id and the day, month and year of the order date, for all orders, in customer id order. Display the supplierOrderDate, the DeliveredDate and the difference in days between the two, for all orders that have been shipped (i.e. deliveredDate is not null)

More exercises Display the order id, the required date, the shipped date where the shipped date is after the required date, the number of days by which it is late, ordered by the number of days by which it is late. Display the orderdate and two weeks after the orderdate for each order that has not been shipped (shippeddate is null).

Exercises Amend the previous exercises to put names on the columns. Format your outputs so that they are easy and pleasant to read. Try out the ‘where’ clause on the sample database, changing the conditions.

Achievements Writing Basic SQL Select Statements –[√]List the capabilities of SQL SELECT statements –[ √ ]Execute a basic SELECT statement Restricting and Sorting Data –[ √] Limit the rows retrieved by a query –[ √] Sort the rows retrieved by a query Single-Row Functions –[ √] Describe various types of functions available in SQL –[ √] Use character, number, and date functions in SELECT statements –[ √] Use conversion functions