Using Relational Databases and SQL Steven Emory Department of Computer Science California State University, Los Angeles Lecture 5: Functions

Miscellany Lab and Homework #3 Questions? Go over some problems? Left and Right Join Comments Which attribute do you check for NULL? Should use the primary key attribute When to Use DISTINCT One-to-many and many-to-many relationships

Topics for Today Functions String Functions (Pages 117 – 120)‏ Date and Time Functions (Pages 120 – 123)‏ Control Flow Functions (Page 125)‏ Comparison Functions (Pages 125 – 126)‏ Numeric Functions (Not in book)‏

What is a Function? Portion of prewritten code in MySQL used to perform a very specific task Syntax: function_name(argument_list)‏ argument_list = [arg1, arg2, arg3,...] Examples: SELECT LENGTH('STEVEN'); -- output is 6 SELECT SIN( ); -- output is 2.6e-6 SELECT CURDATE(); -- output is

Function Tips Don't Try to Memorize Everything Too many functions Every DBMS vendor uses different functions Look them up in the book, on the internet, etc. Get Parentheses Right Type in parentheses first, then fill in the arguments Nested Functions Type each function in separately in notepad When done, substitutes nested functions back in

String Functions CHAR_LENGTH(str)‏ CONCAT(str1, str2,...)‏ CONCAT_WS(separator, str1, str2,...)‏ FORMAT(number, decimal_places)‏ LEFT(str, len), RIGHT(str, len)‏ LOCATE(substr, str), LOCATE(substr, str, pos)‏ LOWER(str), UPPER(str)‏

More String Functions SUBSTRING(str, pos, len)‏ SUBSTRING_INDEX(str, delim, count)‏ TRIM(str), LTRIM(str), RTRIM(str)‏ More string functions can be found here.here.

Date and Time Functions CURDATE()‏ DATEDIFF(date1, date2)‏ DATE_ADD(date, n_days)‏ DATE_ADD(date, INTERVAL value type)‏ DATE_FORMAT(date, format_str)‏ DATE_SUB(date, n_days)‏ DATE_SUB(date, INTERVAL value type)‏

More Date and Time Functions DAYOFMONTH(date), DAY(date)‏ DAYOFWEEK(date)‏ DAYOFYEAR(date)‏ LAST_DAY(date)‏ MONTH(date)‏ NOW()‏ TO_DAYS(date)‏ More date and time functions can be found here.here

Control Flow Functions IF(condition, true_expr, false_expr)‏ IFNULL(expr1, expr2)‏ CASE WHEN expr1 IS NULL THEN expr2 ELSE expr1 END NULLIF(expr1, expr2)‏ CASE WHEN expr1 == expr2 THEN NULL ELSE expr1 END More information on control functions can be found here.here

Cast Functions CAST(expr AS type)‏ CONVERT(expr, type)‏ More information on cast functions can be found here. here

Numerical Functions ABS(value)‏ CEIL(value), CEILING(value)‏ COS(value), SIN(value), TAN(value)‏ DEGREES(value), RADIANS(value), PI()‏ FLOOR(value)‏ POW(X, Y), SQRT(X)‏ ROUND(value), ROUND(value, decimal_places)‏ TRUNCATE(value, decimal_places)‏

Numerical Functions More numerical functions can be found here.here

Sample Questions Report the artist name and member name for each member who is the responsible party for each artist. Concatenate the first and last name of each member with a space between. Modify the previous exercise to also report the home phone number, formatted as (xxx)xxx- xxxx. Report the studio name and the first name of each studio contact. Report the studio name and the last name of each studio contact.

More Sample Questions Report the artist name and the age in years of the responsible member for each artist at the time of that artist's entry date. Report all genres from the Genre table, capitalizing the first letter of each.