Database and table creation

Transcription

1 Database and table creation Introduction SQL - Structured Query Language used to create, modify databases, and to place and retrieve data from databases. SQL was developed in the 70s at IBM. It has become the standard in communication with relational database servers. Many modern relational database uses SQL to communicate with the user, so commonly is said that the use of relational databases means the use of SQL. The first company, which included the SQL to its commercial product, was Oracle. Further introduction of SQL, into the products of other companies, inseparably was associated with the introduction of modifications to the original SQL language. Soon, in order to maintain the uniformity of the language, it was necessary to state the SQL language standard. Use SQL, in accordance with its name, depends on asking queries to the database. Quiries can be assigned to one of three major subsets: SQL DML - Data Manipulation Language, SQL DDL - Data Definition Language, SQL DCL - Data Control Language. SQL key words within the traditionally queries are written in capital letters, but it is not mandatory. As standard, the SQL query is terminated with a semicolon (;, but the harvest in all implementations is mandatory (eg. In TransactSQL Microsoft. In addition, some programs to connect to the database engine (eg. Psql for PostgreSQL, use their own instructions (non-standard SQL eg., to connect to the database, display documentation, etc. How to create database IF DB_ID('DatabaseName' IS NULL CREATE DATABASE DatabaseName -- If database does not exist -- Create database How to delete database IF DB_ID('DatabaseName' IS NOT NULL -- If database exists DROP DATABASE DatabaseName -- drop database Tworzenie tabel The data in a relational database are stored in tables, which are two-dimensional arrays. The tables have been selected as the logical structure of the data storage because of the ease of obtaining and displaying data as well as handling. The tables are created by the command: CREATE TABLE. IF OBJECT_ID('DatabaseName.Owner.TableName','U' IS NULL If table does not exist CREATE TABLE Database.Owner.TableName ( -- then create table column_name type [check], column_name type [check],... REMARKS: 1. Administration database name is not mandatory, for example. CREATE TABLE Owner.TableName The table will then assumed in the current (current database. BAD210 Strona 1

2 2. Mention the owner is also not necessary, for example. CREATE TABLE TableName.. Automatically, the owner of the table will be the user who run the query. 3. If the table has to be accessible to many users, the owner should be given the dbo (database owner, ie. The CREATE TABLE dbo.tablename. Remember that while creating a query we will have to refer to attribute tables. Therefore, we give them the names that carry information about the data they contain. Data types Data types are characterized by a given cell line. They determine what kind of information we can put in the column. For example, another type of data we use when we want to store the user's name, another for the date of his birth, and still another, if we want to keep his picture. Different data types can be classified into different groups according to functionality that may meet: Text data: CHAR, VARCHAR, NCHAR, NTEXT, NVARCHAR Numbers: INT, SMALLINT, BIGINT, TINYINT, FLOAT, REAL, DECIMAL, NUMERIC Date and time: DATETIME, SMALLDATETIME Binary: BINARY, VARBINARY Currency:: MONEY, SMALLMONEY Special: TEXT, IMAGE, XML, BIT The precise definition and explanation of the use of each data type can be found in the help attached to MS SQL Server. Limitations Specific attributes of the created table may have restrictions on the acceptable data: PRIMARY KEY limitation that defines table primary key FOREIGN KEY limitation that defines foreign key (link to the another table, see example below NOT NULL the cell value has to be given (it cannot be empty or NULL CHECK the cell value hast to fit the given range UNIQUE the cell value has to be unique within its column In the following column definition, we determine that the cell value should be a text value consisting of 30 char max, the field will not accept NULL values, and the table primary key is based on that one single column. IF OBJECT_ID('Items','U' IS NULL -- If the table Items does not exist CREATE TABLE Items (Name VARCHAR(30 NOT NULL PRIMARY KEY Another examples: IF OBJECT_ID('Teachers','U' IS NULL --If the table Teachers does not exist CREATE TABLE Teachers( id INT NOT NULL PRIMARY KEY, name VARCHAR(30 CHECK (name LIKE '[A-Z]%', OnDuty VARCHAR(30 CHECK (OnDuty in ('mon', 'tue', 'wed', 'thu', 'fr', salary FLOAT CHECK (salary >= 1000 BAD210 Strona 2

3 IF OBJECT_ID('Students','U' IS NULL -- If the table does not exist CREATE TABLE Students( id INT IDENTITY(1,1 PRIMARY KEY, First Name VARCHAR(10, id_dep INT REFERENCES Departments(id_dep, type VARCHAR(7 CHECK (type in ('daily', 'extramular' DEFAULT 'dzienny', StudyYear INT Table modification Existing table can be modified - adding or removing attributes, as well as adding to their limitations. We use this command to alter the table. IF OBJECT_ID('TableName','U' IS NULL -- If the table does not exist ALTER TABLE TableName <operation> [, <operation> ]; where <operation> = ADD <attrybute definition> - add new attribute (column ADD <limitation> - add new limitation ALTER [COLUMN] <attribute definition> - attribute modification DROP attribute name - delete modification DROP CONSTRAINT limitation name - delete limitation NOTE: Before adding, removing or modifying, the column should be checked whether it exists! Example (add attribute BirthDay to the Teachers table: IF COL_LENGTH('Teachers','BirthDay' IS NULL BithDay does not exist ALTER TABLE Teachers ADD BirthDate SMALLDATETIME -- If the column -- add column How to delete table In order to remove tables (along with the data that is in it, use the command: IF OBJECT_ID('TableName','U' IS NOT NULL -- If the table exists DROP TABLE TableName -- drop table Example: IF OBJECT_ID('Teachers','U' IS NOT NULL DROP TABLE Teachers -- If the table exists -- drop table Please note that we cannot clear the table that contains links to other tables (foreign keys without removing the links first, or removing the tables that are referred to. Create an automatic identifier Very often, we want to define tables that contain the attribute ID which is automatically maintained by the database engine. In this way, while inserting data into the table, we do not have to check whether the ID value is unique. In MS SQL to create the automatic ID attribute it suffices to make to add the limit IDENTITY (START, STEP where the parameter START determines the start number and the setting STEP determines how the value is increased. BAD210 Strona 3

4 IF OBJECT_ID('Students','U' IS NULL -- If the table does not exist CREATE TABLE Students( Id INT IDENTITY(1,1 PRIMARY KEY, -- Automatically increased values FirstName VARCHAR(10, ID_fac INT REFERENCES Faculties(ID_fac, type VARCHAR(7 CHECK (type in ('daily', 'extramular' DEFAULT 'dzienny', StudyYear INT Inserting data INSERT INTO TableName [(attribute, attribute,... ] VALUES (value, value,... Examples: INSERT INTO Authors VALUES (1, 'Marciniak', 'Polska' INSERT INTO Students (Pesel, FirstName, Faculty, StudyYear VALUES (' ', 'Jakub',1, 2 NOTE: We may not give the names of columns, but then we have to provide values for all columns in the appropriate order (the first example. If you do not want to specify all values, because they are eg., default or automatically generated, you must specify the columns for which values are supplied (the second example. Primary keys and foreign keys based on a few columns An example of table with primary key that is based on two columns. IF OBJECT_ID('InvoiceLines','U' IS NULL -- If the table does not exist CREATE TABLE InvoiceLines ( ID INT IDENTITY(1,1, InvoiceNr VARCHAR(10 NOT NULL, -- primary key element --(and foreign key of InvoiceHeaders table LineNr INT NOT NULL, -- primary key element ItemCode VARCHAR(20,..., PRIMARY KEY (InvoiceNr, LineNr, -- Primary key definition FOREIGN KEY InvoiceNr REFERENCES InvoiceHeaders(InvoiceNr Linking other table with the table InvoiceLines with use of the key based on two columns: IF OBJECT_ID('InvoiceLineDetails','U' IS NULL --If the table doesn t exist CREATE TABLE InvoiceLineDetails ( ID INT IDENTITY(1,1, InvoiceNr VARCHAR(10 NOT NULL, -- primary (and foreign key element LineNr INT NOT NULL, -- primary (and foreign key element PropertyID VARCHAR(10 NOT NULL, -- primary key element Value VARCHAR(10, PRIMARY KEY (InvoiceNr, LineNr, PropertyID, -- Primary key definition FOREIGN KEY (InvoiceNr, LineNr REFERENCES InvoiceLines(InvoiceNr, LineNr -- Foreign key definition BAD210 Strona 4

5 Copying of table context 1. Copying data into an existing table Table creation IF OBJECT_ID('InvoiceHistory','U' IS NULL CREATE TABLE InvoiceHistory ( ID INT IDENTITY(1,1, InvoiceNr VARCHAR(10 NOT NULL, ClientNr VARCHAR(10 NOT NULL, If table dosen t exist Data copying INSERT INTO InvoiceHistory (InvoiceNr, ClientNr SELECT (InvoiceNr, ClientNr FROM Invoices WHERE Copying data with table creation SELECT (InvoiceNr, ClientNr INTO InvoiceHistory2 FROM Invoices WHERE... InvoiceHistory2 -- and insert data from table Invoices BAD210 Strona 5

6 Exercises In the following examples red colors indicates the colum(s which create the table primary key.. UWAGA: Do not instert the dbo owner in front of the table name. 1. Create table: SCHOOLS (ID_school, Name, City IF OBJECT_ID(...,'U' IS NULL CREATE TABLE (..., PRIMARY KEY Create table: TEACHERS (ID_teacher, LastName, FirstName, BirthDay, Rate 3. Create table: CLASSES (ID_class, Name, ID_school, ID_teacher, ID_school and ID_teacher are the foreign keys that links to the tables SCHOOLS and TEACHERS. 4. Create table: AFFILIATES (ID_aff, Name, Address, with automatically valued Id_aff. 5. Create table: POSTS(ID_post, Salary_min, Salary_max, Salary_max less than Salary_min Hint: Add CHECK constraint after the table is created. 6. Create table: STAFF (ID_empl, LastName, ID_post, Chief, Empl_date, ID_aff, ID_post is a foreign key referring to the POSTS table, ID_aff is a foreign key referring to the AFFILIATES table. 7. Add a new column 'PostCode' (max 25 characters to the AFFILIATES table. IF OBJECT_ID(...,'U' IS NOT NULL -- If the table exists IF COL_LENGTH(...,'PostCode' IS NULL - If the column does not exist ALTER TABLE... ADD Add column 8. Add a new column 'Pesel' to the STAFF table (max 11 characters 9. Add a limitation (constraint to the 'Pesel' column in the STAFF table only digits have to be accepted. Hint: (Pesel LIKE '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]' IF OBJECT_ID(...,'U' IS NOT NULL -- If the table exists IF COL_LENGTH(...,'Pesel' IS NOT NULL - If the column exists ALTER TABLE... ADD CONSTRAINT CT_Pesel CHECK (... - Alter column 10. Drop column 'PostCode from STAFF table IF OBJECT_ID(...,'U' IS NOT NULL -- If the table exists IF COL_LENGTH(...,'PostCode' IS NOT NULL - If the column exists ALTER TABLE... - Drop column 11. Insert data into tables AFFILIATES, POSTS, STAFF by copying them from the tables BRANCHES, POSITIONS, EMPLOYEES and the following queries INSERT INTO AFFILIATES (... SELECT... FROM BRANCHES INSERT INTO POSTS (... SELECT... FROM POSITIONS INSERT INTO STAFF (... SELECT... FROM EMPLOYEES BAD210 Strona 6