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Up to now, you have seen how the select command can be used to retrieve records from a table. However, our basic examples have all retrieved every record from the table. If you want to see only certain rows, you must add a where clause.
Since our previous examples returned every record in the table, we created a simple table with a few rows in it for illustration purposes. Had we chosen to illustrate the select command against the large sample tables provided by Oracle, we would have returned thousands of rows—far too many for listing in this chapter. Now that we are introducing the where clause, we will be able to control the output. As a result, the remaining examples in this chapter will now use the customers, products, sales, and costs tables that are part of the Oracle sample database. Let's describe each of these tables.
SQL> desc customers; Name Null? Type ----------------------------------------- -------- ------------------- CUST_ID NOT NULL NUMBER CUST_FIRST_NAME NOT NULL VARCHAR2(20) CUST_LAST_NAME NOT NULL VARCHAR2(40) CUST_GENDER NOT NULL CHAR(1) CUST_YEAR_OF_BIRTH NOT NULL NUMBER(4) CUST_MARITAL_STATUS VARCHAR2(20) CUST_STREET_ADDRESS NOT NULL VARCHAR2(40) CUST_POSTAL_CODE NOT NULL VARCHAR2(10) CUST_CITY NOT NULL VARCHAR2(30) CUST_CITY_ID NOT NULL NUMBER CUST_STATE_PROVINCE NOT NULL VARCHAR2(40) CUST_STATE_PROVINCE_ID NOT NULL NUMBER COUNTRY_ID NOT NULL NUMBER CUST_MAIN_PHONE_NUMBER NOT NULL VARCHAR2(25) CUST_INCOME_LEVEL VARCHAR2(30) CUST_CREDIT_LIMIT NUMBER CUST_EMAIL VARCHAR2(30) CUST_TOTAL NOT NULL VARCHAR2(14) CUST_TOTAL_ID NOT NULL NUMBER CUST_SRC_ID NUMBER CUST_EFF_FROM DATE CUST_EFF_TO DATE CUST_VALID VARCHAR2(1) SQL> desc products; Name Null? Type ----------------------------------------- -------- ------------------- PROD_ID NOT NULL NUMBER(6) PROD_NAME NOT NULL VARCHAR2(50)
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