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Transcript
SQL • Structured Query Language (SQL) is an industrystandard language used for creating, updating and querying relational databases • SQL operations are based on relational algebra that underlies relational database design • SQL is a 4th Generation non-procedural language (whereas C and COBOL are 3rd generation procedural languages; Assembler language is 2nd generation; Machine language is 1st generation) • SQL is non-procedural – language does not contain procedural constructs like loops, if-then-else, functions, etcetera Extended Versions of SQL • Standard SQL is available on all relational DBMS including IBM’s DB2, Oracle Corporation’s Oracle, Microsoft’s SQL Server and Access, Open Source’s MySQL • However most Database Management Systems (DBMS) provide non-standard extensions to SQL that include procedural elements • IBM’s extended versions of SQL include SQL/400 and SQL/DS • Oracle’s extension to SQL is called PL/SQL • SQL Server’s extension is called Transact-SQL SQL Subsets • 3 subsets of SQL statements: – Data Definition Language (DDL) : used to define objects such as collections, tables and views – Data Manipulation Language (DML): Used to modify data in a database – Data Control Language (DCL): used to control access to database objects • Main focus in DBS201: DDL to define a database • Main focus of DBS301: DML to retrieve and manipulate data in a database SQL DDL Statements (DBS201) Data Definition Language (DDL) is used to define objects: • CREATE (COLLECTION, TABLE or VIEW): defines a collection, table, or view to the DBMS • DROP (COLLECTION, TABLE or VIEW): removes definition of a collection, table or view from the DBMS • ALTER TABLE: modifies the definition of a table SQL DML Statements (DBS201) • INSERT: adds a row of data to a table • SELECT: displays data from one or more tables or views (presented in part in DBS201 – will mainly be covered in DBS301) • DELETE: removes data from a table Create Table with Primary Key Syntax: CREATE TABLE table_name ( fieldname datatype (length, decimals), fieldname2 datatype (length, decimals, fieldname3 datatype (length, decimals), CONSTRAINT constraint_name PRIMARY KEY (column name) ) Example: CREATE TABLE STUDENT (StudNo NUMERIC (9, 0), LastName CHAR (20), First_Name CHAR (20), Program CHAR (4) CONSTRAINT Student_PK PRIMARY KEY(StudNo) ) Insert Row of Data into a Table Syntax: INSERT INTO table_name VALUES(value1, value2…) where number, sequence and data-type of values must correspond exactly to columns in table Example: INSERT INTO Student VALUES(123456789, ‘Wong’, ‘Susan’, ‘CPD’) Insert Row of Data into a Table Syntax: INSERT INTO table_name(Column_name2, column_name1) VALUES(value2, value1…) where number and sequence of values does not have to correspond to columns in table Example: INSERT INTO Student(LastName,StudNo,FirstName) VALUES(‘Smith’, 111111111, ‘Bill’) Exercise • Write the SQL command to create a table called Supplier. It should have 3 columns, Supplier Number - a 5-digit number, Supplier Name – max length 25 characters, Supplier Rating – a number from 1 to 5. The primary key will be supplier number. • Write the SQL command to insert a row of data into the supplier table.