SQL Cookbook

Chapter 1. Retrieving Records

This chapter focuses on very basic SELECT statements. It is important to have a solid understanding of the basics as many of the topics covered here are not only present in more difficult recipes but also are found in everyday SQL.

1.1. Retrieving All Rows and Columns from a Table

Problem

You have a table and want to see all of the data in it.

Solution

Use the special “*” character and issue a SELECT against the table:

	1 select *
	2   from emp

Discussion

The character “*” has special meaning in SQL. Using it will return every column for the table specified. Since there is no WHERE clause specified, every row will be returned as well. The alternative would be to list each column individually:

	select empno,ename,job,sal,mgr,hiredate,comm,deptno
	  from emp

In ad hoc queries that you execute interactively, it’s easier to use SELECT *. However, when writing program code it’s better to specify each column individually. The performance will be the same, but by being explicit you will always know what columns you are returning from the query. Likewise, such queries are easier to understand by people other than yourself (who may or may not know all the columns in the tables in the query).

1.2. Retrieving a Subset of Rows from a Table

Problem

You have a table and want to see only rows that satisfy a specific condition.

Solution

Use the WHERE clause to specify which rows to keep. For example, to view all employees assigned to department number 10:

 1 select * 2 from emp 3 where ...