in-line view to get tablespace usage
The inline view is a
construct in Oracle SQL where you can place a query in the SQL FROM,
clause, just as if the query was a table name.
A common use for
in-line views in Oracle SQL is to simplify complex queries by removing
join operations and condensing several separate queries into a single
query. The best example of the in-line view is the common Oracle DBA
script that is used to show the amount of free space and used space within
all Oracle tablespaces. Let’s take a close look at this SQL to see how
it works. Carefully note that the FROM clause in this SQL query specifies
two sub-queries that perform summations and grouping from two views,
dba_data_files, and dba_free_space.
In ANSI standard SQL,
it is quite difficult to compare two result sets that are summed together
in a single query, and this is a common problem with Oracle SQL where
specific values must be compared to a summary.
Without the use of an in-line view, several separate SQL queries
would need to be written, one to compute the sums from each view and
another to compare the intermediate result sets.
This is a great report
for display the actual amount of free space within an Oracle tablespace.
"Tablespace" format a13
This SQL quickly
compares the sum of the total space within each tablespace to the sum of
the free space within each tablespace. Here is a sample of the output:
Used MB Free MB Total MB
Basically, this query
needs to compare the sum of total space within each tablespace with the
sum of the free space within each tablespace.
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