How To Create A Table In Sql (Ahem)

Transcription

1 Database Systems Unit 5 Database Implementation: SQL Data Definition Language Learning Goals In this unit you will learn how to transfer a logical data model into a physical database, how to extend or modify the structure of an existing database, how to ensure data integrity, and how to control access to the data in the database. DB / PRM1 / db07_sql_ddl.ppt / Version

2 Languages Implementation of tables and other objects of a database system is done by data definition language (DDL) statements. Insertion, Modification and Deletion of the objects of a database system is done by data manipulation language (DML) statements Both sublanguages are included in SQL (Structered Query Language). DB / PRM1 / db07_sql_ddl.ppt / Version Implementation CREATE DATABASE... USER... TABLE... VIEW... INDEX GRANT CREATE PROCEDURE... FUNCTION... TRIGGER Operation INSERT UPDATE SELECT DELETE GRANT REVOKE Maintenance & Optimization CREATE / ALTER / DROP... TABLE... VIEW... INDEX... FUNCTION... PROCEDURE... TRIGGER... USER... DATABASE GRANT / REVOKE DB / PRM1 / db07_sql_ddl.ppt / Version

3 Databases and Schemas Usually, a database system maintains more than one database Within one database, the objects (tables etc.) may be grouped into different schemas. Database objects are named uniquely within the same schema To specify objects in another schema, you have to use a qualified name, the schema name and the object name separated by a period, e.g., "CarDB.Car" (except for objects in the default schema) To specify objects in another database, it has to be qualified with the database and schema name, e.g., "t4a.prm.employee" DB / PRM1 / db07_sql_ddl.ppt / Version Databases and Schemas CREATE SCHEMA company AUTHORIZATION JSMITH; In general, not all users are authorized to create schemas and schema elements. The privilege to create schemas, tables, and other constructs must be explicitely granted to the relevant user assounts by the system administrator or DBA. In addition to the concept of a schema, SQL-92 uses the concept of a catalog a named collection of schemas in an SQL environment. A SQL environment is basically an installation of an SQL-compliant RDBMS on a computer system. DB / PRM1 / db07_sql_ddl.ppt / Version

4 CREATE TABLE Commands in SQL CREATE TABLE company.table ; The relations declared through CREATE TABLE statements are called base tables (or base relations); this means that the relation and its tuples are actually created and stored as a file by the DBMS.. Base relations are distinguished from virtual relations, created through the CREATE VIEW statement, which may or may not correspond to an actual physical file. In SQL the attributes in a base table are considered to be ordered in the sequence in which they are specified in the CREATE TABLE statement. DB / PRM1 / db07_sql_ddl.ppt / Version CREATE TABLE Commands in SQL CREATE TABLE table (column-definition [, column-definition table-constraint...]); column-defintion = column datatype [ [NOT] NULL ] [ [DEFAULT constant_expression] [IDENTITY [(seed, increment)] ] ] [ column-constraint ] DB / PRM1 / db07_sql_ddl.ppt / Version

5 CREATE TABLE Commands in SQL CREATE TABLE employee ( FNAME VARCHAR(15) NOT NULL, LNAME VARCHAR(15) NOT NULL, SSN CHAR(9) NOT NULL, BDATE DATE, ADDRESS VARCHAR(15), SEX CHAR, SALARY DECIMAL(10,2), SUPERSSN CHAR(9), DNO INT NOT NULL DEFAULT 1, ); DB / PRM1 / db07_sql_ddl.ppt / Version Alphanumeric CHAR(n) Fixed-length non-unicode character data with a maximum length of 8'000 characters VARCHAR(n) Variable-length non-unicode character data with a maximum of 8'000 characters TEXT Variable-length non-unicode data with a max. length of characters NCHAR / NVARCHAR / NTEXT represent the same types as above, but for Unicode characters (maximal capacity is half as specified above) DB / PRM1 / db07_sql_ddl.ppt / Version

6 Numeric Values: Integers and Floating Point Values BIGINT Integer values from through INT Integer values from through SMALLINT Integer values from through TINYINT Integer values from 0 through 255 FLOAT[(n)] Floating point values from -1.79E+308 to -2.23E-308, 0 and 2.23E-308 to 1.79E+308 n (1 to 53) is the nb. of bits for the mantissa REAL -3.40E+38 to -1.18E-38, 0 and 1.18E-38 to 3.40E+38 DB / PRM1 / db07_sql_ddl.ppt / Version Decimal and Numeric DECIMAL[(p[, s])] Fixed precision and scale numeric values from through Specifies the maximum total number of decimal digits that can be stored, both to the left and to the right of the decimal point The precision (p) must be a value from 1 through the maximum precision The scale (s) specifies the maximum number of decimal digits that can be stored to the right of the decimal point NUMERIC[(p[, s])] Functionally equivalent to Decimal DB / PRM1 / db07_sql_ddl.ppt / Version

7 Date and Time DATETIME Date and time values from January 1, 1753, through December 31, 9999, with an accuracy of threehundredths of a second, or 3.33 milliseconds SMALLDATETIME Date and time data from January 1, 1900, through June 6, 2079, with an accuracy of one minute DB / PRM1 / db07_sql_ddl.ppt / Version Money MONEY Monetary data values from through , with accuracy to 1/10'000 of a monetary unit SMALLMONEY Monetary data values from -214, through +214, , with accuracy to 1/10'000 of a monetary unit DB / PRM1 / db07_sql_ddl.ppt / Version

8 SQL Data Types Overview Access SQL-Server Oracle MySQL PostgreSQL boolean Yes/No Bit Byte N/A Boolean Integer Number (integer) Int, BigInt Smallint, Tinyint, Numeric, Decimal Number Numeric Int Integer (synonyms) Integer Int float Number (single) Float, Real Number Float Numeric currency Currency Money, Smallmoney N/A N/A Money string (fixed) N/A Char, NChar Char Char Char string (variable) Text (<256) Memo (65k+) Varchar NVarchar Varchar Varchar2 Varchar Varchar binary object Date & Time OLE Object Memo Date/Time Binary (fixed up to 8K) Varbinary (<8K) Image (<2GB) DateTime SmallDateTime Timestamp Long Raw (<2GB) Date Timestamp Blob Text Date, Time, DateTime Timestamp Binary Varbinary Date, Time Timestamp Interval DB / PRM1 / db07_sql_ddl.ppt / Version Binary Data and Semi-Structured Data BINARY(n) Binary data with fixed length n between 1 and 8000 VARBINARY(n) Binary data with variable length (maximal n) between 1 and 8000 IMAGE Binary data with a maximal size of XML New in SQL Server 2005; Used to store XML documents or fragments DB / PRM1 / db07_sql_ddl.ppt / Version

9 CREATE TABLE Commands in SQL CREATE DOMAIN ssn_type AS CHAR(9); A domain can be declared, and the domain name used with the attribute specification. This makes it easier to change the data type for a domain that is used by numerous attributes in a schema and improves schema readability. We can use ssn_type in place of CHAR(9). DB / PRM1 / db07_sql_ddl.ppt / Version The Constraint Concept Constraints are properties or predicates assigned to a column or a set of columns within a table They specify integrity rules and prevent that values that do not fulfill the rules may be inserted in the table Technically we differentiate between Column-Constraints Part of the column-definition and only affecting this column Table-Constraints Defined independently from the column definitions and may affect multiple columns DB / PRM1 / db07_sql_ddl.ppt / Version

10 Constraints and Data Integrity Constraints may be used to enforce different types of data integrity, namely: Entity Integrity ensures that there are no duplicate rows in a table Domain Integrity enforces valid entries for a given column by restricting the type, the format, or the range of possible values Referential integrity ensures that rows may not be deleted, when they are referenced by other rows User-Defined Integrity enforces some specific business rules that do not fall into entity, domain, or referential integrity categories DB / PRM1 / db07_sql_ddl.ppt / Version Syntax for a Column Constraint [ CONSTRAINT constraint-name ] { [ NULL NOT NULL ] [ PRIMARY KEY UNIQUE ] [ REFERENCES RefTable [(RefColumn)] [ON DELETE {CASCADE NO ACTION}] [ON UPDATE {CASCADE NO ACTION}] CHECK (boolean-expression) } DB / PRM1 / db07_sql_ddl.ppt / Version

11 Syntax for a Column Constraint: Example CREATE TABLE departement ( DNAME VARCHAR(15) NOT NULL, DNUMBER INT PRIMARY KEY, MGRSSN CHAR(9) NOT NULL, MGRSTARDATE DATE, ); DB / PRM1 / db07_sql_ddl.ppt / Version Table Constraint [ CONSTRAINT constraint-name ] { [ { PRIMARY KEY UNIQUE } (column-list) ] [ FOREIGN KEY (column-list) REFERENCES RefTable [(RefColumn)] [ON DELETE {CASCADE NO ACTION}] [ON UPDATE {CASCADE NO ACTION}] CHECK (boolean-expression) } DB / PRM1 / db07_sql_ddl.ppt / Version

12 Table Constraint: Example CREATE TABLE Employee ( Lastname VARCHAR(30) NOT NULL, Firstname VARCHAR(30) NOT NULL, DeptId INT NOT NULL, CONSTRAINT PK_Employee PRIMARY KEY (Lastname, Firstname), CONSTRAINT FK_Emp_Dept FOREIGN KEY (DeptId) REFERENCES Department(Id) ON DELETE SET DEFAULT ON UPDATE CASCADE, ); DB / PRM1 / db07_sql_ddl.ppt / Version Primary Key Constraint A PRIMARY KEY constraint is a unique identifier for a row within a database table Every table should have a primary key constraint to uniquely identify each row Only one primary key constraint can be created for each table The primary key constraints are used to enforce entity integrity Most DBMS provide a mechanism to create unique key values without any semantical meaning (e.g., Identity) DB / PRM1 / db07_sql_ddl.ppt / Version

13 Foreign Key Constraint A FOREIGN KEY constraint is a reference from one table to another (or the same) A foreign key in one table points to a primary key in another table Foreign keys enforce referential integrity by preventing violating actions (NO ACTION; default) cascading delete or update actions (CASCADE) In the latter case a referential triggered action is specified; alternatives are SET NULL, SET DEFAULT. DB / PRM1 / db07_sql_ddl.ppt / Version Foreign Key Constraint The action for SET NULL or SET DEFAULT is the same for both on ON DELETE or ON UPDATE; the value of the affected referncing attributes is changed to NULL for SET NULL, and to the specified default value for SET DEFAULT. ON DELETE CASCADE is to delete all the referencing tuples. ON UPDATE CASCADE is to change the value of the foreign key to the updated (new) primary value for all referencing tuples. DB / PRM1 / db07_sql_ddl.ppt / Version

14 Unique Constraint A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered The unique key constraints are used to enforce entity integrity as the primary key constraints Unique constraints are also often used for the candidate keys which have not been chosen to be the primary key. Typically, the attributes to be unique are then declared with the NOT NULL modifier. DB / PRM1 / db07_sql_ddl.ppt / Version Check Constraint A CHECK constraint is used to limit the values that can be stored in a given column (Column constraint) It may also be used to prevent invalid or senseless value combinations within rows (Table constraint) The check constraints are used to enforce domain integrity and/or business rules The argument of a check constraint is a simple or complex boolean expression containing one or more attributes and to be satisfied by the attribute values of each tuple contained in the table. DB / PRM1 / db07_sql_ddl.ppt / Version

15 Syntax for a Column Constraint: Example CREATE TABLE departement (, DNUMBER INT NOT NULL CHECK (DNUMBER>0 AND DNUMBER<21), ); DB / PRM1 / db07_sql_ddl.ppt / Version Schema Change Statements in SQL DROP SCHEMA company {CASCADE RESTRICT}; If the RESTRICT option is chosen in place of CASCADE, the schema is dropped only if it has no elements in it; otherwise, the DROP command will not be executed. DROP TABLE table {CASCADE RESTRICT}; If the RESTRICT schema is chosen instead of CASCADE, a table is dropped only if it is not referenced in any constraints (for example, by foreign key definitions in another relation) or views. With the CASCADE option, all such constraints and views that refernce the table are dropped automatically from the schema. DB / PRM1 / db07_sql_ddl.ppt / Version

16 Schema Change Statements in SQL ALTER TABLE company.employee ADD job VARCHAR(12); The definition of a base table can be changed by using the ALTER command. This command adds a new column to the table ALTER TABLE company.employee DROP address {CASCADE RESTRICT}; If the RESTRICT is chosen, the command is successful only if no views or constraints reference the column. With the CASCADE option, all such constraints and views that reference the table are dropped automatically from the schema. DB / PRM1 / db07_sql_ddl.ppt / Version Schema Change Statements in SQL ALTER TABLE table { ADD column-definition table-constraint [, column-definition table-constraint...] ALTER COLUMN column-definition DROP constraint DROP COLUMN column } DB / PRM1 / db07_sql_ddl.ppt / Version

17 Commands for Manipulation the Database in SQL ALTER TABLE company.employee ADD job VARCHAR(12); The definition of a base table can be changed by using the ALTER command. This command adds a new column to the table ALTER TABLE company.employee DROP address {CASCADE RESTRICT}; If the RESTRICT is chosen, the command is successful only if no views or constraints reference the column. With the CASCADE option, all such constraints and views that reference the table are dropped automatically from the schema. DB / PRM1 / db07_sql_ddl.ppt / Version SQL Queries SELECT <ATTRIBUTE ANF FUNCTION LIST> FROM <TABLE LIST> [WHERE <CONDITION>] [GROUP BY <GROUPING ATTRIBUTE(S)>] [HAVING <GROUP CONDITION>] [ORDER BY <ATTRIBUTE LIST>] ; DB / PRM1 / db07_sql_ddl.ppt / Version

18 The SELECT clause lists the attributes or functions to be retrieved The FROM clause specifies all relations (tables) needed in the query, including joined relations. The WHERE clause specifies the conditions for selection of tuples from these relations, inclduing joined conditions if needed. DB / PRM1 / db07_sql_ddl.ppt / Version SQL Queries SELECT FNAME, LNAME FROM EMPLOYEE; Lists all the name pairs of the employees. SELECT * FROM EMPLOYEE; List all attributes of each each employee tuple. SELECT FNAME, LNAME FROM EMPLOYEE WHERE SEX = M; Lists all male employees. DB / PRM1 / db07_sql_ddl.ppt / Version

19 SQL Queries GROUP BY specifies grouping attributes to partition the set of tuples into a set of subgroups. HAVING specifies a condition on the groups being selected rather than on the individual tuples. Finally, ORDER BY specifies an order for displaying the result of a query. The built-in aggregate functions COUNT, SUM, MIN, MAX, and AVG are usually used in conjunction with grouping, but they can also be applied to all the selected tuples in a query without a GROUP BY clause. DB / PRM1 / db07_sql_ddl.ppt / Version SQL Queries SELECT FNAME, EMPLOYEE.NAME FROM EMPLOYEE, DEPARTEMENT WHERE DEPARTEMENT.NAME= Research AND DEPARTEMENT.DNUMBER=EMPLOYEE.DNUMBER; If a query refers to two or more attributes with the same name, we must qualify the attribute name with the relation name to prevent ambiguity. DB / PRM1 / db07_sql_ddl.ppt / Version

20 SQL Queries SELECT E.FNAME, E.LNAME,S.FNAME, S.LNAME FROM EMPLOYEE AS E, EMPLOYEE AS S WHERE E.SUPERSSN=S.SSN; It is possible to declare alternative relation names, called aliases or tuple variables (here E and S for the EMPLOYEE relation). DB / PRM1 / db07_sql_ddl.ppt / Version SQL Queries SELECT SSN, DNAME FROM EMPLOYEE, DEPARTEMENT; This statement produces all the combinations of EMPLOYEE SSN and DEPARTEMENT DNAME. SELECT * FROM EMPLOYEE, DEPARTEMENT; This statement produces the cross product of both relations. DB / PRM1 / db07_sql_ddl.ppt / Version

21 SQL Queries SELECT ALL SALARY FROM EMPLOYEE; This statement generates possibly duplicate tuples. Duplicates are not eliminated SELECT DISTINCT SALARY FROM EMPLOYEE; This statement eliminates duplicate tuples. DB / PRM1 / db07_sql_ddl.ppt / Version The Concept of Indexes The order of tuples in a relation is not defined! Searching in unsorted data is very slow (linear search). Indexes are constructs that speed up searching or ordering of data in tables given a specific subset of attributes. We may declare more than one index for one and the same relation. In most RDBMS, the presence of indexes is transparent to users and programmers. DB / PRM1 / db07_sql_ddl.ppt / Version

22 Creating and Removing Indexes Create a new index: CREATE [UNIQUE] INDEX index ON table (column [ASC DESC] [,column [ASC DESC]...]); Remove an existing index: DROP INDEX Tablename.index; DB / PRM1 / db07_sql_ddl.ppt / Version Unique and not-unique Index Indexes may be helpful or even necessary in the following cases: unique indexes for the primary keys of all tables, unique indexes for candidate keys, non-unique indexes for often used foreign keys, and non-unique indexes for specific sort orders and search procedures. Most DBMS automatically create indexes for primary keys, for foreign keys with forced referential integrity, and for unique constraints. DB / PRM1 / db07_sql_ddl.ppt / Version

23 Remarks The DROP INDEX statement does not apply to indexes automatically created by the system for constraint specifications All indexes are bound to exactly one table; dropping this table also drops any index defined on the table DB / PRM1 / db07_sql_ddl.ppt / Version DB / PRM1 / db07_sql_ddl.ppt / Version