Mastering Oracle SQL

DML Statements

In this section, we introduce the four statements that comprise the DML portion of SQL. The information presented in this section should be enough to allow you to start writing DML statements. As is discussed at the end of the section, however, DML can look deceptively simple, so keep in mind while reading the section that there are many more facets to DML than are discussed here.

The SELECT Statement

The SELECT statement is used to retrieve data from a database. The set of data retrieved via a SELECT statement is referred to as a result set . Like a table, a result set is comprised of rows and columns, making it possible to populate a table using the result set of a SELECT statement. The SELECT statement can be summarized as follows:

SELECT <one or more things>
FROM <one or more places>
WHERE <zero, one, or more conditions apply>

While the SELECT and FROM clauses are required, the WHERE clause is optional (although you will seldom see it omitted). We therefore begin with a simple example that retrieves three columns from every row of the customer table:

               SELECT cust_nbr, name, region_id
               FROM customer; CUST_NBR NAME REGION_ID ---------- ------------------------------ ---------- 1 Cooper Industries 5 2 Emblazon Corp. 5 3 Ditech Corp. 5 4 Flowtech Inc. 5 5 Gentech Industries 5 6 Spartan Industries 6 7 Wallace Labs 6 8 Zantech Inc. 6 9 Cardinal Technologies 6 10 Flowrite Corp. 6 11 Glaven Technologies 7 12 Johnson Labs 7 13 Kimball Corp. 7 14 Madden Industries 7 15 ...