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. Cnnect t MySql using MySqlWrkbench 2 4. Create Tables web_user and user_rle 2 5. Add Freign Key frm Table web_user t Table user_rle 4 6. Add Data t Table user_rle (and Get Primary Key Vilatin) 5 7. Add Data t Table web_user (and Get Freign Key Vilatin) 6 8. SELECT Data 7 9. Jin Data 9 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). There is a separate dcument which reviews database terms and cncepts. 3. 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. 4. 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 2

3 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 3

4 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. 5. 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 4

5 6. 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 5

6 7. 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 6

7 8. 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 7

8 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 8

9 9. 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 9