Slide 15.2: SQL SELECT statement (cont.)

Slide 15.1: SQL SELECT statement
Slide 15.3: SQL SELECT statement (cont.)
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SQL SELECT Statement (Cont.)

SELECT Examples
Some of SELECT examples are given next.

☠ Caution ☠: NOT all SQL commands are supported by Oracle. For a complete Oracle SQL command list, check Oracle Database SQL Language Quick Reference.

Let R be a relational schema with a set of attributes X, where {A₁, ..., A_k} is contained in X. The project of R onto {A₁, ..., A_k} is expressed by
SELECT DISTINCT A1, ... Ak FROM R; SQL> SELECT DISTINCT class FROM student;

Let R and S be relational schemata with equal sets of attributes. The union of R and S is expressed by

SELECT DISTINCT * FROM R UNION SELECT DISTINCT * FROM S;

SQL> SELECT DISTINCT * FROM ( SELECT last_name FROM student )
  2    UNION
  3  SELECT DISTINCT * FROM ( SELECT first_name FROM student );

Let R be as in the previous slide, where A and B are in X. The selection of R with respect to condition A = a is expressed by

SELECT DISTINCT * FROM R WHERE A = a;

SQL> SELECT DISTINCT last_name FROM student WHERE class = 2;

The selection with respect to condition A = B is expressed by

SELECT DISTINCT * FROM R WHERE A = b;

SQL> SELECT DISTINCT first_name FROM student WHERE class = student_id;

Demonstration
Below is an SQL test area from W3Schools, which uses the well-known Northwind sample database. The tables here are for read only because of the problem of embedding the scripts. For a fully working example, check this by using Chrome.

Result:

The Database includes:

Tablename	Record
Customers	91
Categories	8
Employees	10
OrderDetails	518
Orders	196
Products	77
Shippers	3
Suppliers	29

W3C WebSQL

WebSQL Browser Support