你可以使用COUNT(DISTINCT col1 || '-' || col2)，但如果列是字符串值，并且你有'ab-'||'-'|...
oracle数据库才会给我们统计基于表的统计信息 --在指定for all columns 和不指定任何参数的时候oracle会给所有字段做统计信息,在指定for indexed columns时,oracle只给[b]有索引的字段进行字段信息统计[/b],如果我们别有必要给所有字段统计信息时,这个属性就很有用了. --再综合前面的我们就会发现,如果在运行analyze...
distinct; 使用表达式定义的字段; 伪列rownum; 原表在视图中未选择(未select)的字段的所有数据为非空且无默认值。 当然,并非只要SQL语句中包含了这6个子句或条件,就无法对视图进行全部DML。规则如下: 删除视图记录。要求SQL语句中不能包含前3个子句或条件。 修改视图记录。要求SQL语句中不能包含前5个子句...
all values found by the subquery are used for pivoting. The output isnot the same cross-tabular format returned by non-XML pivot queries. Instead ofmultiple columns specified in the pivot_in_clause, the subquery produces asingle XML string column. The XML string for each row holds aggregated...
In the past, classic reports rendered when the result set contained multiple columns with the same name. In Application Express 18.1, the column names of the query result set must be unique, otherwise a "Column Ambiguously Defined" error occurs. You must change any non-unique report queries pr...
2.Bitmap based count distinct SQL Function 基于位图的COUNT DISTINCT SQL函数 在19c 中,SQL 功能获得了进一步的增强,这其中包括对于 COUNT DISTINCT的进一步优化,在12c中引入的近似 Distinct 操作已经可以为特定SQL带来极大性能提升,现在基于位图的COUNT DISTINCT 操作继续为查询加速 ...
Introduced in ECC V12, a Summary line is displayed for aggregated table metrics at the footer for all records for: Sum, Min, Max, Count, Count Distinct and Average. This summary is impacted by any selected refinement and local filters. Example of a Summary Line at the Footer of the Aggre...
WHERE clause constraints are evaluated on the data before it is grouped. HAVING clause constraints are evaluated on the results of the data after it has been grouped together. You can specify multiple columns in a GROUP BY clause. For example, the following query includes the city and descripti...
multiblock (up to DB_FILE_MULTIBLOCK_READ_COUNT blocks) reads due to full scans into the buffer cache show up as waits for 'db file scattered read'. Check the following V$SESSION_WAIT parameter columns: P1: The absolute file number P2: The block being read P3: The number of blocks (...
Hence a count of 50,000 in the “0 access” bucket. It seems like a viable explanation – but we might want to fiddle with slightly different queries, and do some tests of multiple executions of the same query (while the data changes), and some tests with slightly different but ...