CODEWITHSUNDEEP
javajdbcresultset
Steve McLeod
Steve McLeod

Reputation: 52448

How do I get the row count in JDBC?

I've executed a JDBC query to obtain a resultset. Before iterating over it, I'd like to quickly find out how many rows were returned. How can I do this with high performance?

I'm using Java 6, Oracle 11g, and the latest Oracle JDBC drivers.

Upvotes: 32

Views: 100738

Answers (7)

Tom Hawtin - tackline
Tom Hawtin - tackline

Reputation: 147124

If your driver supports it(!), you can call ResultSet.afterLast() ResultSet.getRow() ResultSet.beforeFirst(). Performance may or may not be good.

A better solution would be to rewrite your algorithm not to require the size up front.

Upvotes: 4

v8-E
v8-E

Reputation: 1105

Without ternary operator 

rs.last();  // Moves the cursor to the last row in this ResultSet object.
int rowCount = rs.getRow();  //Retrieves the current row number.
rs.beforeFirst(); //Moves the cursor to the front of this ResultSet object,just before the first row.

With ternary operator one line 

int rowCount = rs.last() ? rs.getRow() : 0; 
rs.beforeFirst();

Upvotes: 2

MindBrain
MindBrain

Reputation: 7768

Code:

//Create a Statement class to execute the SQL statement
Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery("SELECT COUNT(*) AS COUNT FROM
TABLENAME");

 while(rs.next()) {
    System.out.println("The count is " + rs.getInt("COUNT"));
 }

 //Closing the connection
 con.close();

Upvotes: 0

user2594537
user2594537

Reputation: 251

To get the number of rows from JDBC:

ResultSet rs = st.executeQuery("select count(*) from TABLE_NAME");
rs.next();
int count = rs.getInt(1);

Upvotes: 21

thezar
thezar

Reputation: 1298

ResultSet rs = stmt.executeQuery(sql);
int rowCount = rs.last() ? rs.getRow() : 0; // Number of rows in result set. Don't forget to set cyrsor to beforeFirst() row! :)

Upvotes: 23

cletus
cletus

Reputation: 625007

You're going to have to do this as a separate query, for example:

SELECT COUNT(1) FROM table_name

Some JDBC drivers might tell you but this is optional behaviour and, more to the point, the driver may not know yet. This can be due to how the query is optimised eg two example execution strategies in Oracle are to get all rows as quickly as possible or to get the first row as quickly as possible.

If you do two separate queries (one a count and the other the query) then you'll need to do them within the same transaction. This will work well on Oracle but can be problematic on other databases (eg SQL Server will either show you uncommitted data or block on an external uncommitted update depending on your isolation level whereas Oracle supports an isolation level that gives you a transactionally consistent view of the data without blocking on external updates).

Normally though it doesn't really matter how many rows there are. Typically this sort of query is either batch processed or paged and either way you have progress information in the form of rows loaded/processed and you can detect the end of the result set (obviously).

Upvotes: 34

Jon Skeet
Jon Skeet

Reputation: 1499800

Short answer: you can't.

Long answer: you can't, partly because the database may be lazily evaluating the query, only returning rows as you ask for them.

EDIT: Using a scrollable ResultSet you can :)

Indeed, I asked this very question in the Java databases newsgroup a long time ago (back in 2001!) and had some helpful responses.

Upvotes: 20

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