18.6 DATABASE QUERIES
Oracle uses a structured query language (SQL) to enable you to search the database objects and gather the information you need. The format of the database statements follows a specific syntax that includes the command, object, and source table from which to extract the data. In order to extract the data using SQL, you could execute a pre-existing script, write a script that contains the SQL statements you need, or execute the SQL statement at the database command line.
18.6.1 Basics of Writing SQL Statements
The following is true of SQL statements: Begin at the SQL prompt Can be entered on one or more lines Line wraps are indicated with a number at the beginning of the continued line Are not case sensitive, unless indicated Clauses are usually placed on separate lines for readability and editing Tabs and indents can be used to make the code more readable Keywords cannot be split across lines or abbreviated Keywords typically are entered in uppercase All other words, such as table names and columns, are lowercase One statement can be entered at a time for processing End with semicolon Choose the rows in a table Choose the columns in a table Select data from multiple tables
18.6.2 Examples of Database Queries using SQL
Login to the database. Use the sqlplus command to execute several SQL statements: # sqlplus
SQL*Plus: Release 9.2.0.2.0 - Production on Sat Jan 10 12:57:48 2004
Copyright © 1982, 2002, Oracle Corporation. All rights reserved.
Enter user-name: opc_op/opc_op@ov_net
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.2.0 - 64bit Production
JServer Release 9.2.0.2.0 - Production
SQL> select count(*) from opc_act_messages;
COUNT(*)
139
SQL>
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