Exam 4 Review: SQL, pymysql, and XML CS 2316 Fall 2011

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1 Exam 4 Review: SQL, pymysql, and XML CS 2316 Fall 2011 This is a nn-exhaustive list f tpics t study. Yu will be held respnsible fr all readings n the curse website and lecture cntents even if they are nt mentined n this (nn-cmplete) review sheet. Basic SQL Table name: players playerid name psitin 21 Je QB Jacks n 13 Gerge DE Burdell 1 Rn Hwar d DT SELECT T extract infrmatin that already exists in the database. SELECT field names desired FROM table name WHERE cnditin T select all the fields, use SELECT * The WHERE clause is ptinal Field names and table names are typically case sensitive INSERT T insert new infrmatin int the database INSERT INTO table name(fieldname1, fieldname2) VALUES (value1, value2) If yu will insert a value fr each field, then yu can use: INSERT INTO table name VALUES (value1, value2, value3) UPDATE T update an already existing database entry UPDATE table name SET fieldname1 = value1, fieldname2 = value2 WHERE cnditin The WHERE clause is nce again ptinal DELETE T delete an existing entry

2 DELETE FROM table name WHERE cnditin There are varius functins yu can use with SQL. Things like: MAX and MIN Suppse yu want t find the maximum and minimum weight f a ftball player in the table abve. SELECT MAX(weight), MIN(weight) AVG and SUM Yu can find the average r sum f a given clumn. Fr example: SELECT AVG(weight), SUM(weight) COUNT Cunt will return the cunt f the number f rws returned. Suppse I wanted t cunt the number f quarterbacks n the team. SELECT COUNT(*) WHERE psitin = QB COUNT(*) was used, but COUNT(playerID) wuld have als wrked. COUNT will nly cunt rws that d nt have NULL values, s it is a gd idea t cunt n the key r anther field that cannt be NULL LIKE Using the LIKE keywrd allws us t place further cnditins nt strings. Suppse I wanted t return the infrmatin fr any player that has the last name f Brwn. SELECT * WHERE name LIKE %Brwn The % acts as a wildcard and represents any amunt f characters in its place. If I wanted t allw fr Brwn t be fund anywhere in the string, I wuld use LIKE %Brwn% GROUP BY ORDER BY GROUP BY is an peratr that can be placed at the end f a SQL query. It allws yu t grup rws tgether based n a certain criteria. Suppse I wanted t find the average weight fr each ftball psitin: SELECT psitin, AVG(weight) GROUP BY psitin

3 The ORDER BY keywrd is used t srt n a specific clumn. The default is t srt in ascending (ASC) rder, but yu can als specify t srt descending (DESC) Suppse I wanted t return the player infrmatin in alphabetical rder: SELECT * ORDER BY name Suppse I wanted t return the player infrmatin in the rder f heaviest player first: SELECT * ORDER BY weight DESC Using a database with pythn In CS 2316, we use the pymysql mdule t cnnect t SQL databases. T cnnect t a database, we use the fllwing cmmand: db = pymysql.cnnect(hst = hstname.cm, passwd = 'passwrd', user = username,db= databasename ) By ding this, a reference t the database is nw stred in db, which we need t execute queries. T execute a query, we need t use a cursr. First, yu need t initiate a cursr: mycursr = db.cursr() Let s say I want t insert a new player int my players table. myquery = INSERT INTO players VALUES (%s, %s, %s, %s) The %s are acting as placehlders fr values that I will give the query. Instead f hard-cding the player s infrmatin, I will allw myself flexibility t insert multiple players with the same query. Nw, I need t execute the query: mycursr.execute(myquery, ( 42, Jhn Grisham, QB, 110 )) The secnd parameter f mycursr.execute is a tuple f what I want t insert int my placehlders (%s).

4 Since I just inserted new infrmatin int the database, it wuld be a gd idea t cmmit my changes. Yu shuld d this every time yu finish yur wrk with the database: db.cmmit() Let s say that instead, I wanted t get infrmatin frm the database all the players infrmatin. Frm befre, we knw that the query t use is: query = SELECT * mycursr.execute(query) Nw, the infrmatin I want is stred within mycursr, but hw d I get it ut? There are a few methds: firstrw = mycursr.fetchne() Nw, a tuple cntaining the first rw f infrmatin gathered is stred in firstrw. firstrw = (21, Je Jacksn, QB, 220) allrws = mycursr.fetchall() Nw, a tuple cntaining a tuple representing each rw is stred in allrws allrws = ((21, Je Jacksn, QB, 220), (13, Gerge Burdell, DE, 270), (1, Rn Hward, DT, 350)) Use a fr lp t add entries t a list: mylist = [] fr entry in mycursr: mylist.append(entry) This methd wuld generally be useful if yu wanted t d sme srt f cnditinal check in yur fr lp as yu are prcessing the data. After yu are finished using yur cursr, remember t clse it! D this by: mycursr.clse() Fr practice: Write a functin, givemeinf, which will cnnect t a database, retrieve all the rws in a table, and return the infrmatin in a list f lists. Yu can make up the database infrmatin, but use the table name basicinf.

5 Write a functin, insertnewplayers, which will insert new player infrmatin int ur players table. The functin will take in a parameter, playerinf, which is a list f lists f the player infrmatin, and a parameter, db, which is the database bject. The list culd be f any length. Yu shuld insert all the infrmatin int the table. Ex playerinf list: [[43, Bb Bradley, RB, 210], [91, Cl Kid, TE, 250]] XML The XML mdule in pythn shuld be imprted as fllws: imprt xml.etree.elementtree as et Imprting a mdule as anther name allws fr quicker access. Yu can read abut XML fundamentals in the curse ntes: Here is an example functin that creates a XML tree. imprt xml.etree.elementtree as et def myxml(): Grandmther = et.element("grandma", age="90", name="kathleen") mytree = et.elementtree(grandmther) Mther = et.subelement(grandmther, "Mm", age="50", name="ruth") Mther.text = "Clean yur rm!" Aunt = et.element("aunt", num="54", letter="cathy") Grandmther.append(Aunt) Yu = et.subelement(mther, "Yu", age="20", name="bb") Yu.text = "I hate cleaning my rm!" Nte that a subelement can be added t an XML tree in tw ways: 1. Yu can create the element separately and later append it t its parent. myel = et.element( thisname ) rt.append(myel) 2. Yu can create it as a subelement, fr which yu specify its parent as the first parameter: myel = et.subelement(rt, thisname ) Here are sme things yu can d with an XML tree: Let s say I wanted t get sme infrmatin abut Mther Mther.attrib -> returns a dictinary f the attributes. In this case, { age : 50, name : Ruth } Mther.text -> returns the text cntained in the xml tag

6 Clean yur rm! If I wanted t write the XML tree ut t a file, I wuld use mytree.write( filename.xml, UTF-8 ) UTF-8 is the encding type f the file. Alternatively, t pen an xml file, I wuld use: mytree = et.parse( filename.xml ) Then, t find the rt f mytree: myrt = mytree.getrt() What if I want t find a certain branch f the tree? fundbranch = myrt.find( Branch Name ) Fr practice, draw ur what this tree wuld lk like. Practice Prblems (Pssible) Slutins: imprt pymysql def givemeinf(): db = pymysql.cnnect(hst = 'myhst.edu', passwd = 'passwrd', user = 'cs2316', db='cs2316db') query = "SELECT * FROM basicinf" mycursr = db.cursr() mycursr.execute(query) mylist = [] # Create big list t return fr rw in mycursr: # Iterate thrugh the cursr rwlist = [] # Fr every rw, start a new list fr item in rw: # Iterate thrugh each item in the rw rwlist.append(item) # Add each item t the rw list mylist.append(rwlist) # Append the rw list t the new list mycursr.clse() db.cmmit() return rwlist def insertnewplayers(playerinf, db): mycursr = db.cursr() query = "INSERT INTO players VALUES(%s, %s, %s, %s)"

7 fr player in playerinf: mycursr.execute(query, (str(player[0]), str(player[1]), str(player[2]), str(player[3]))) mycursr.clse() db.cmmit()