Oracle Database

Here are some frequently used queries for histograms in Oracle How to check the endpoint values for the histograms SELECT ENDPOINT_NUMBER, ENDPOINT_VALUE, COLUMN_NAME FROM DBA_HISTOGRAMS WHERE TABLE_NAME=’&table_name’ AND owner=’&owner’; How to check the type of histogram created select COLUMN_NAME,NUM_DISTINCT,NUM_BUCKETS,HISTOGRAM from DBA_TAB_COL_STATISTICS where table_name=’&table_name’ and owner=’&table_owner’ order by column_name; How to check details for the frequency …

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Histograms are generated in Oracle by using the method_opt parameter in the dbms_stats procedure method_opt syntax FOR ALL [INDEXED | HIDDEN] COLUMNS [size_clause] FOR COLUMNS [column_clause] [size_clause] size_clause is defined as size_clause := SIZE {integer | REPEAT | AUTO | SKEWONLY} column_clause is defined as column_clause := column_name | extension name | extension – integer : …

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In this post, we will see the important topic of histograms in Optimizer stats What is a histograms in Oracle A histogram is a special type of column statistic that provides more detailed information about the data distribution in a table column. By gathering histogram data, the CBO can make improved selectivity estimates in the …

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Sometimes, we may need to set the optimizer statistics preferences at the table level. We will check in detail about it How to set table level preference setting The DBMS_STATS.SET_TABLE_PREFS procedure is used to set the statistics preferences of the specified table in the specified schema. Syntax DBMS_STATS.SET_TABLE_PREFS ( ownname IN VARCHAR2, tabname IN VARCHAR2, …

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Suppose you want to set up method_opt preference for the schema, then the below procedure can be done to set it up The  DBMS_STATS.SET_SCHEMA_PREFS procedure is used to set the statistics preferences of all the tables owned by the specified owner name. DBMS_STATS.SET_SCHEMA_PREFS (ownname IN VARCHAR2,pname IN VARCHAR2,pvalue IN VARCHAR2) Example exec DBMS_STATS.SET_SCHEMA_PREFS(‘SCOTT’, ‘method_opt’,’for all …

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