MySqlWorkbench Tutorial: Creating Related Database Tables

Transcription

1 MySqlWrkbench Tutrial: Creating Related Database Tables (Primary Keys, Freign Keys, Jining Data) Cntents 1. Overview 2 2. Befre Yu Start 2 3. Review Database Terms and Cncepts 2 4. Cnnect t MySql using MySqlWrkbench 4 5. Create Tables web_user and user_rle 4 6. Add Freign Key frm Table web_user t Table user_rle 6 7. Add Data t Table user_rle (and Get Primary Key Vilatin) 7 8. Add Data t Table web_user (and Get Freign Key Vilatin) 8 9. Selecting Data Jining Data Dcument yur Wrk 12 Page 1

2 1. Overview After reviewing database terms, yu will use MySqlWrkbench t create a database with 2 tables (custmer and prduct) and enter test data int bth f these tables. Yu will learn abut primary keys (aut-increment and nt aut-increment) and primary key cnstraints. Yu will als learn hw t write and execute simple (single table) SQL select statements. 2. Befre Yu Start There is a separate dcument that tells yu hw t install MySqlWrkbench n yur PC/MAC. MySqlWrkbench is a GUI (Graphical User Interface) frnt end t the MySql database management system (which runs n a temple database server). 3. Review Database Terms and Cncepts A table cntains data abut bjects f a particular type r entity. Examples f entities are Custmers, Prducts. The rws in a table are called recrds. The clumns in a table are called fields r attributes. Clumns may have cnstraints. Fr example, when yu define a clumn as being f data type Date (and it is a required field), this means that the database has a cnstraint that says, n recrd may be added unless it has a valid date in that field. If yu specify anther clumn as being 20 characters, the database will nt allw a recrd t be added if it has mre than 20 characters in that field. Each table shuld have a primary key, which is ne r mre fields that uniquely identifies a recrd within the table. When yu specify a primary key, yu are setting up a cnstraint that says this table shall nt cntain mre than ne recrd with the same primary key value as anther recrd (in the same table). A table may have zer r mre freign keys which pint t anther recrd (in the same r different table). When yu specify a freign key (with integrity enfrced ), yu are setting up a cnstraint that says n freign key value can pint t a nn-existing recrd. A database is a cllectin f related tables. When we design a database, we determine which tables need t be included fr a given applicatin, what fields r attributes are needed fr each table, and hw thse tables shuld be related. A database management system (DBMS) is system sftware that encapsulates the database. There is n way t add, edit, delete, r even view the data unless yu g thrugh the database management system. Yu can think f the DBMS as the buncer at a night club. Nbdy unauthrized gets in. N actins (e.g., updates) are allwed if they wuld break the rules (cnstraints). As we specify the field types and specific relatinships between tables, this creates cnstraints t be enfrced by the Data base management system (e.g., MSAcess). The DBMS ensures that nly valid data ges in (e.g., valid dates in date fields, valid numbers in number fields), there are n duplicate primary key values in any table, and there are n invalid freign key values (ne recrd pinting t anther recrd that des nt exist). Page 2

3 The example belw shws a database with tw tables: an Emplyee table and a Department table. The Emplyee table cntains 7 rws (als called recrds r bjects), each representing a particular Emplyee. There are 8 clumns in the Emplyee table (clumns are als called fields r attributes) s, that means we knw 8 pieces f data (first name, last name, address, etc.) abut each Emplyee in ur table. In ur example, Emp_ID has been specified as the primary key. Once a certain field (r fields) is specified as primary key, the DBMS will never allw tw recrds with the same primary key value t be stred in a table. In ur example, the Emplyee table has ne freign key field, Dept_ID that pints t a recrd in the Department table. Once we tell the DBMS that a freign key f ne table pints t the primary key f anther table, the DBMS will ensure that there is never a pinter t nwhere. Emplyee Table Emp_ID Last_name First_name Emplyee_Adrs City State zip_cde Dept_ID 1 Paquette Je 2224 Web Blvd Centralia WA Jhnsn Fred 410 Deer Ave Centralia WA Bradish Emily 512 Plaza Place Seattle WA Braak Jhn 112 N Lincln Centralia WA Shuster Gerge 5003 Cuntry Ln Centralia WA Tate Frank 603 Pinecrest Rd Chehalis WA Department Table Dept_ID Dept_name Dept_Expense_Act 1 Marketing Sales Service Manufacturing Given the abve data (with primary keys and freign keys specified), the DBMS will prevent the fllwing actins. Cannt add this recrd int the Emplyee table (Duplicate Primary Key). Emp_Id = 7 is already there. Emp_ID Last_name First_name Emplyee_Adrs City State zip_cde Dept_ID 7 Smith Mary 123 Any St Chehalis WA Cannt add this recrd int the Emplyee table (Invalid Freign Key). There is n Department with Dept_Id = 888 Emp_ID Last_name First_name Emplyee_Adrs City State zip_cde Dept_ID 8 Smith Mary 123 Any St Chehalis WA Cannt delete (wuld create invalid freign key fr several Emplyee Recrds that have Dept_ID = 5) Dept_ID Dept_name Dept_Expense_Act 5 Service Page 3

4 Using a Database cncept called JOIN, yu can extract data that LOOKS redundant data (see belw), but there is n actual redundancy within the database (n cpies f data stred). SELECT Last_name, First_Name, Emplyee_Adrs, Emplyee.Dept_Id, Dept_Name FROM Emplyee, Department WHERE Emplyee.Dept_ID = Department.Dept_ID Last_name First_name Emplyee_Adrs Dept_ID Dept_Name Paquette Je 2224 Web Blvd 6 Manufacturing Jhnsn Fred 410 Deer Ave 1 Marketing Bradish Emily 512 Plaza Place 5 Seattle Braak Jhn 112 N Lincln 6 Manufacturing Shuster Gerge 5003 Cuntry Ln 1 Marketing Tate Frank 603 Pinecrest Rd 5 Chehalis 4. Cnnect t MySql using MySqlWrkbench There is a separate dcument that tells yu hw t find yur database credentials and cnnect t the database that was created fr yur use in yur class. It s a little invlved the first time since yu have t find yur database passwrd, etc. 5. Create Tables web_user and user_rle Using MySqlWrkbench, lcate then duble click n yur database schema (left pane under SCHEMAS ). Yur schema will then becme bld indicating that this is the default database. Then pen up yur schema and right click n Tables (under yur database schema), then select create table. The blded database schema is the default schema. Duble click t select yurs (therwise yu ll have t prefix every table name with yur schema name in yur SQL cde). Right click Tables Select Create Table Page 4

5 Frm the New Table windw, enter the new table name ( web_user ), check that InnDB is selected fr database engine InnDB (s freign keys will wrk), and pen up the tw chevrns s that there is space t enter in the clumns fr the web_user table. Click the chevrns s yu can enter in the clumns. Muse ver the abbreviatins abve the check bxes t learn the varius attributes f database table clumns: PK: Primary Key (unique identifier f each recrd within the table) NN: Nt Null (nt allwed t be null, means it is a required field fr the user t enter) UQ: field must be unique within the table. AI: Aut-increment. The database management system supplies the next available number (autmatically) the user des nt have t enter a value int this field. Then enter in the clum names, data types, and attributes f the web_user table exactly as shwn. Yu will be getting sample cde all semester that expects this table t be just s. Create a secnd table named user_rle with clumns and attributes (exactly) as shwn: If yu ever need t mdify the design f ne f yur tables, right click n the table, then select Alter Table. If yu are nt seeing a table that yu just created, right click n Tables and select Refresh All. Page 5

6 When yu design a database table, Typically yu will have ne clumn that is the primary key (PK, NN). By naming cnventin, the name f this field shuld be tablename_id. A primary key may ften be aut-increment (AI) which means that the database management system is in charge f allcating a unique number t each recrd as the recrds are inserted. In this tutrial, ne f the tables (web_user) has an aut-increment primary key, but the ther (user_rle) des nt. This is t shw yu the difference between the tw typical design chices. Fr ther clumns, specify the desired data type. Here are sme f the nrmal types are: VARCHAR: specify the maximum size f a string t be stred. INT: this is a nrmal integer. Specify the maximum number f digits t be stred. DECIMAL: this is the best data type t stre currency. It s stred like an integer (nt real number/flating pint number), but with the decimal pint mved t the left a certain number f digits. Specify the maximum digits and the number f digits t the right f the decimal pint. DATE: this is the data type t use (nt DATETIME) if yu just want t stre day/mnth/year. DATETIME Is mre cmplicated t use it includes hurs/minutes/secnds/millisecnds and it requires mre effrt t cnvert and frmat. In ur data mdel, we want each web_user recrd t indicate which user_rle they are. T implement this, we add field user_rle_id t table web_user (type matching user_rle.user_rle_id) and in the next step we will turn that field int a freign key (like a pinter). It is a database naming cnventin t name a freign key field the same as the primary key that it references. 6. Add Freign Key frm Table web_user t Table user_rle A freign key is like a pinter. T create a freign key frm web_user.user_rle_id t user_rle.user_rle_id, type the fllwing SQL int the Query area then click n the execute icn (lightning blt). Nte: if the query area is clsed/disabled, right click n ne f yur tables and chse Select Rws. This will pen a query windw. Then replace that SQL (e.g., SELECT * FROM web_user ) with the SQL yu want t run. If there is an errr, yu shuld see a message at the bttm f the utput windw. Verify that yu created the freign key by right clicking n table web_user, selecting Alter Table, and clicking n the Freign Keys tab. Yu shuld see an autmatically named freign key listed there. Page 6

7 7. Add Data t Table user_rle (and Get Primary Key Vilatin) T add data int table user_rle, right click that table and select the tp ptin Select Rws. Enter 2-3 recrds int table user_rle then click Apply. Yur data desn t have t match what s belw. Try t enter a recrd that has the same user_rle_id as a recrd already in the table (and click Apply ). Since this wuld vilate the Primary Key (PK) cnstraint that yu specified fr the user_rle.user_rle_id, the database management system will give an errr (like belw). This is ne f the main jbs f a database management system t prevent cnstraint vilatins, t prtect the integrity f the database. Page 7

8 8. Add Data t Table web_user (and Get Freign Key Vilatin) Right click n table web_user and enter ne recrd. Nte: Leave the web_user_id field empty. We designed this field as aut-increment which means we want the database management system t assign the next available (unique) number whenever we insert a recrd. Enter the date in this frmat: YYYY-MM-DD. Dn t put cmmas in the decimal field (membership_fee). Enter a web_user.user_rle_id value that matches ne f the values in user_rle.user_rle_id. Click Apply and cnfirm that the recrd gt inserted. Nw enter 3-5 mre web_user recrds - all with empty web_user_id, sme with empty birthday, sme with empty membership_fee, all with valid user_rle_id (values fund in user_rle.user_rle_id). Click Apply and cnfirm that all recrds were inserted (if any ne is rejected, all are rejected until yu fix it). Try t enter a web_user recrd that has an invalid user_rle_id (a value that is nt fund in user_rle.user_rle_id). This shuld cause a freign key cnstraint vilatin and the database management system will give an errr like this: Page 8

9 9. SELECT Data T extract data frm the database use the SQL SELECT statement. The data that is returned by running a SELECT statement is called a result set. Type yur SQL int the windw as shwn, then click n Query Execute r click n the lightning blt icn. The first statement (USE) specifies which database schema we are using. If yu have selected yur schema frm the default database schema pick list, yu d nt need t enter the USE statement. The secnd statement (SELECT) indicates that we want t see all the clumns (*) frm the table. Since n WHERE clause is used, all recrds are shwn and we see a green check mark that cnfirms the syntactically crrect SQL was executed. If yur SQL had a syntax errr, yu wuld see an errr message at the bttm f the windw, in the utput area (smetimes a little hard t ntice). In the example belw, I misspelled the table name and yu can see a very descriptive errr message. Page 9

10 Instead f using *, yu can specify which clumns yu want t see by listing them ut. Yu can specify the rder yu want t see in the result set by adding an ORDER BY clause. Yu can specify which recrds yu want t see by adding a WHERE clause. Yu can split a SQL statement int multiple lines. At the end f each SQL statement, yu need a ; Page 10

11 10. Jin Data Relatinal databases are all abut nt having any redundancy. This is why we wuld nt put user_rle_id and user_rle_type directly int the web_user table. Instead we keep data abut user_rles in the user_rle table and simply pint web_user recrds t the prper user_rle recrd. T shw related data, we use a JOIN. The JOIN can be written using a WHERE clause (as belw) r an INNER JOIN (belw that) bth yielding the same result set. When ne field name is in mre than ne table in a SELECT statement, yu must use a table name prefix fr thse ambiguus fields (e.g., user_rle_id which is in bth tables). Page 11

12 11. Dcument yur Wrk Create a wrd dcument and paste in the red text belw t be used t label yur answers. Then paste yur answers (frm MySql Wrkbench) after each label. Nte that it is hard t read (t small) if yu cpy/paste entire screen shts, s paste int a prgram like MSPaint first, then just cpy ut the part that has been requested (as I have dne t create this tutrial). Wrth 1 pint: a) Table design f user_rle (Alter Table) b) All rws, all clumns f user_rle (SELECT *) c) Primary Key cnstraint errr generated by the DBMS when trying t insert a duplicate user_rle_id int the user_rle table Wrth 3 pints: d) Table design f web_user (Alter Table) e) Freign key tab f the web_user table design (shwing the freign key yu created) f) All rws, all clumns f web_user (SELECT *) g) Freign Key cnstraint errr generated by the DBMS when trying t insert a web_user recrd with an invalid user_rle_id Wrth 3 pints: h) Jin f web_user table with user_rle table shwing clumns user_ , user_passwrd, user_rle_id, user_rle_type, web_user_id srted by user_ (use WHERE r INNER JOIN) i) Nte: because user_rle_id is an ambiguus clumn name given the tables in this SELECT statement, yu must prefix this clumn name with a table name Jin f web_user table with user_rle table shwing clumns web_user_id, user_ , user_passwrd, srted by web_user_id but nly fr sme f the web_user recrds filtered by _address. HINT: use single qute when cmparing with character data like this: WHERE user_ _address > 'd' Page 12