SQL SQL stands for Structured Query Language SQL allows you to access a database SQL is an ANSI standard computer language SQL can execute queries against.
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SQL SQL stands for Structured Query Language SQL allows you to access a database SQL is an ANSI standard computer language SQL can execute queries against a database SQL can retrieve data from a database SQL can insert new records in a database SQL can delete records from a database SQL can update records in a database
History Was designed and implemented by IBM Research (1986) A joint with American National standards Institute (ANSI) and International Standards Organization (ISO) led to the standard version of SQL-86 A revised and expanded in 1992 called SQL-92. Most recent is now SQL-99
Definitions and Data Types Uses terms table, rows, columns for the formal relational model terms relations, tuple, and attribute. An SQL schema is identified by a schema name, including authorization identifier to indicate user who owns it and descriptions for each element. Schema elements include tables, constraints, views, domains, and other constructs Catalog – a named collection of schemas in an SQL environment
Common Data Types char (size) – Fixed length character string. Size is specified in parenthesis. Max 255 bytes. varchar (size) – Variable-length character string. Max size is specified in parenthesis. number (size) – Number value with a max number of column digits specified in parenthesis. date – Date value number (size, d) – Number value with a max number of digits of “size” total, with a max number of “d” digits to the right of the decimal.
Creating Tables Create Table – used to specify a new relation by giving it a name, and attributes with initial constraints. – Example: CREATE TABLE company.employee … Company is the schema name Employee is the relation name
Creating a Table Create table myemployees (firstname varchar(30), lastname varchar(30), title varchar (30), age number(2), salary number(8, 2)); Creates a table called myemployees First name, last name, and title allows 30 characters each. Age is allowed 2 digits Salary is allowed 8 digits with 2 decimals
Other Functions Select – allows you to select a certain and retrieve data specified. – Example: Select “column1” From “TableName” Where “condition”; Select column 1 from the TableName with the following condition.
Insertion Insert into “tablename” (first_column, … last_column) values (first_value,…last_value); Insert into employee (first, last, age, address, city, state) values (‘James’, ‘Tran’, 23, ‘1111 1 st street’, ‘San Jose’, ‘California’); Inserts into specified table name Specify all columns inserting to separated by a comma. Values inserted are specified afterwards Strings enclosed in single quotes, numbers are not.
Updating update “tablename” set “columnname” = “newvalue” [,”nextcolumn” = “newvalue2”…] where “columnname” OPERATOR “value” [and | or “column” OPERATOR “value”]; **[ ] = optional Update the specified table name Set the column specified with new value Add in conditionals if needed Optional values and input add [ ]
Deleting delete from “tablename” where “columnname” OPERATOR “value” [and | or “column” OPERATOR “value”]; [ ] = optional Delete a certain table, column, row, etc. Operator meaning >,<,=, etc…
Drop Dropping a table removes all rows and definitions. Example: Drop table “TableName”
Ordering SQL allows you to order elements in a table. Example: orders by alphabetical select distinct customer-name from borrower, loan where borrower.loan-number = loan.loan- number and branch-name = ‘Perryridge’ order by customer-name
Aggregates More functions that allow you to operate on sets. – COUNT, SUM, AVG, MAX, MIN Produces numbers, not tables. Not part of relational algebra – Example: Select MAX (Age) From Employee E
Grouping Sometimes we want to apply aggregate functions to subgroups of tuples in a relation. Such as finding the average salary of employees in each department or the number of employees that are working on each project. SQL has a GROUP BY clause that allows for specific grouping of attributes
Grouping Cont Example: – SELECT Dno, COUNT(*), AVG (Salary) FROM EMPLOYEE GROUP BY Dno; – The EMPLOYEE tuples are partitioned into groups, each group having the same value for the grouping attribute Dno. – Then the COUNT and AVG functions are applied to each group.
A A1 A2 A4 A5 A A1 A2 A3 A4 A A1 A2 A3 A4 A5 Two tables a) b) R(A) UNION ALL S(A) c) d) A A2 A3 A A2 A3 R(A) EXCEPT ALL S(A) R(A) INTERSECT S(A) SQL Multiset Operations SR T T T
Nested Queries List all courses that were not taught in S2000 SELECT C.CrsName FROM Course C WHERE C.CrsCode NOT IN (SELECT T.CrsCode --subquery FROM Teaching T WHERE T.Sem = ‘S2000’) Evaluation strategy: subquery evaluated once to produces set of courses taught in S2000. Each row (as C) tested against this set.