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I have a .jsp page where I have a GUI table that displays records from an Oracle database. This table allows typical pagination behaviour, such as "FIRST", "NEXT", "PREVIOUS" and "LAST". The records are obtained from a Java ResultSet object that is returned from executing a SQL statement.
This ResultSet might be very big, so my question is:
If I have a ResultSet containing one million records but my table only displays the data from the first ten records in the ResultSet, is the data only fetched when I start requesting record data or does all of the data get loaded into memory entirely once the ResultSet is returned from executing a SQL statement?
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Invoke the Statement. executeQuery method to obtain the result table from the SELECT statement in a ResultSet object. In a loop, position the cursor using the next method, and retrieve data from each column of the current row of the ResultSet object using getXXX methods.
A table of data representing a database result set, which is usually generated by executing a statement that queries the database. A ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row.
Hence, when a Java programmer needs to determine if ResultSet is empty or not, it just calls the next() method and if next() returns false it means ResultSet is empty.
An SQL result set is a set of rows from a database, as well as metadata about the query such as the column names, and the types and sizes of each column. Depending on the database system, the number of rows in the result set may or may not be known.
The Java ResultSet is a pointer (or cursor) to the results in the database. The ResultSet loads records in blocks from the database. So to answer your question, the data is only fetched when you request it but in blocks.
If you need to control how many rows are fetched at once by the driver, you can use the setFetchSize(int rows) method on the ResultSet. This will allow you to control how big the blocks it retrieves at once.
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