An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
he USING clause is used to specify with the column to test for equality when two tables are joined.
[sql]Select * from table1 join table2 using table1 ID[/sql]
table1 tables join with the table2 tables with the tableID.
Hash Cluster is a technique used for storing the table to make it faster to retrieve. It order to retrieve the rows from the table, apply the hash value on the table.
Hot backup is taking backup of archived log files when database is open.THe ARCHIVE LOG switch should be enabled for this to happen. Hot backup happens while the database is still being accessed by users and tables are being updated. It does not need the database to have a downtime.
You can use ROWID to fetch Row from the table. The use of ROW ID is the fastest query method for fetching data from the table.
Aggregate function is a function where values of multiple rows or records are joined together to get a single value output.
Common aggregate functions are :-
When the database is created in Oracle database system, it automatically generate a SYSTEM named SYSTEM tablespace. The SYSTEM tablespace contains data dictionary tables for the entire database.
Components of physical database structure are given below:
The optimizer determines the most efficient way to execute a SQL statement based on the kind of data in the table and the statements fired to fetch that data like indexes, full table sc, loops, joins etc. Optimizers are also used to avoid excessive I/O resources.