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http://viralpatel.net/blogs/useful-oracle-queries/
Here’s a list of 40+ Useful Oracle queries that every Oracle developer must bookmark. These queries range from date manipulation,getting server info,get execution status,calculate database size etc.
Date / Time related queries
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Get the first day of the month
Quickly returns the first day of current month. Instead of current month you want to find first day of month where a date falls,replace SYSDATE with any date column/value.
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Get the last day of the month
This query is similar to above but returns last day of current month. One thing worth noting is that it automatically takes care of leap year. So if you have 29 days in Feb,it will return 29/2. Also similar to above query replace SYSDATE with any other date column/value to find last day of that particular month.
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Get the first day of the Year
First day of year is always 1-Jan. This query can be use in stored procedure where you quickly want first day of year for some calculation.
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Get the last day of the year
Similar to above query. Instead of first day this query returns last day of current year.
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Get number of days in current month
Now this is useful. This query returns number of days in current month. You can change SYSDATE with any date/value to know number of days in that month.
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Get number of days left in current month
Below query calculates number of days left in current month.
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Get number of days between two dates
Use this query to get difference between two dates in number of days.
Use second query if you need to find number of days since some specific date. In this example number of days since any employee is hired.
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Display each months start and end date upto last month of the year
This clever query displays start date and end date of each month in current year. You might want to use this for certain types of calculations.
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Get number of seconds passed since today (since 00:00 hr)
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Get number of seconds left today (till 23:59:59 hr)
Data dictionary queries
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Check if a table exists in the current database schema
A simple query that can be used to check if a table exists before you create it. This way you can make your create table script rerunnable. Just replace table_name with actual table you want to check. This query will check if table exists for current user (from where the query is executed).
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Check if a column exists in a table
Simple query to check if a particular column exists in table. Useful when you tries to add new column in table using ALTER TABLE statement,you might wanna check if column already exists before adding one.
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Showing the table structure
This query gives you the DDL statement for any table. Notice we have pass ‘TABLE’ as first parameter. This query can be generalized to get DDL statement of any database object. For example to get DDL for a view just replace first argument with ‘VIEW’ and second with your view name and so.
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Getting current schema
Yet another query to get current schema name.
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Changing current schema
Yet another query to change the current schema. Useful when your script is expected to run under certain user but is actually executed by other user. It is always safe to set the current user to what your script expects.
Database administration queries
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Database version information
Returns the Oracle database version.
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Database default information
Some system default information.
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Database Character Set information
Display the character set information of database.
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Get Oracle version
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Store data case sensitive but to index it case insensitive
Now this ones tricky. Sometime you might querying database on some value independent of case. In your query you might do UPPER(..) = UPPER(..) on both sides to make it case insensitive. Now in such cases,you might want to make your index case insensitive so that they don’t occupy more space. Feel free to experiment with this one.
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Resizing Tablespace without adding datafile
Yet another DDL query to resize table space.
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Checking autoextend on/off for Tablespaces
Query to check if autoextend is on or off for a given tablespace.
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Adding datafile to a tablespace
Query to add datafile in a tablespace.
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Increasing datafile size
Yet another query to increase the datafile size of a given datafile.
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Find the Actual size of a Database
Gives the actual database size in GB.
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Find the size occupied by Data in a Database or Database usage details
Gives the size occupied by data in this database.
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Find the size of the SCHEMA/USER
Give the size of user in MBs.
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Last SQL fired by the User on Database
This query will display last SQL query fired by each user in this database. Notice how this query display last SQL per each session.
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Performance related queries
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CPU usage of the USER
Displays CPU usage for each User. Useful to understand database load by user.
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Long Query progress in database
Show the progress of long running queries.
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Get current session id,process id,client process id?
This is for those who wants to do some voodoo magic using process ids and session ids.
- V$SESSION.SID AND V$SESSION.SERIAL# is database process id
- V$PROCESS.SPID is shadow process id on this database server
- V$SESSION.PROCESS is client PROCESS ID,ON windows it IS : separated THE FIRST # IS THE PROCESS ID ON THE client AND 2nd one IS THE THREAD id.
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Last SQL Fired from particular Schema or Table:
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Find Top 10 SQL by reads per execution
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