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I know that my objects must have statistics gathered on them for the CBO to work. How do I use the ANALYZE command to determine access statistics?<p><B>1 Technique</B><p>Use the ANALYZE TABLE command to gather statistics on a table and all associated indexes. The syntax of several different ANALYZE commands are shown in <A HREF="image/04oht20.gif">Figure 4.20</A>. These will be used to gather and remove statistics for Oracle抯 Cost Based optimizer.<p>There are two main options of the ANALYZE table command: ESTIMATE and COMPUTE. ESTIMATE looks at a sample of records in a table and determines various statistics about the data of the table, which is explained later in this How-To. Although ESTIMATE looks at only a sample of data, usually 25% or less, COMPUTE looks at every record in a table. Although this takes considerably more time, the statistics that it gathers may be more accurate. Which method to use will depend on which is more important梩he speed to collect statistics or the accuracy of the statistics.<p><B>Steps</B><P><B>1.</B>	Connect to SQL*Plus as the WAITE account. If you have not done so already, create the EMPLOYEE04 table by running the CHP4_1.SQL script. At this point, there will be no records in the table. To get a better grasp of how statistics on tables work, create some sample data in the table.<p><B>2.</B>	Run CHP4_18.SQL, shown in <A HREF="image/04oht21.gif">Figure 4.21</A>, to create sample data.<p><code><b>SQL> START CHP4_18.sql<p>1 row created.<p>1 row created.<p>2 rows created.<p>4 rows created.<p>8 rows created.<p>16 rows created.<p>SQL></b></code><p><B>3.</B>	At this point, 32 records will be in the EMPLOYEE04 table but no statistics. Run CHP4_19.SQL to estimate statistics, sampling 25% of the records.<p><code><b>SQL> GET CHP4_19.sql<p>1  ANALYZE TABLE EMPLOYEE04<p>2  ESTIMATE STATISTICS SAMPLE 25 PERCENT;<p>SQL> /<p>Table analyzed.<p>SQL></b></code><p><B>4.</B>	Now that the table has been analyzed, you may view the statistics that have been gathered. Run the CHP4_20.SQL script to see a few statistics.<p><code><b>SQL> GET CHP4_20.sql</b></code><table border=0 cellpadding=3 cellspacing=3><TR><td><code><b>1</b></code></TD><TD><code><b>SELECT NUM_ROWS,</b></code></TD> <TD><code><b>AVG_SPACE,</b></code></TD> <TD><code><b>SAMPLE_SIZE,</b></code></TD> <TD><code><b>AVG_ROW_LEN</b></code></TD></TR><TR><td><code><b>2</b></code></TD><TD colspan=4><code><b>FROM DBA_TABLES</b></code></TD></TR><TR><td><code><b>3</b></code></TD><TD colspan=5><code><b>WHERE TABLE_NAME = 慐MPLOYEE04
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