Using the JDBC Driver¶
This topic provides information about how to use the JDBC driver.
Snowflake JDBC API extensions¶
The Snowflake JDBC driver supports additional methods beyond the standard JDBC specification. This section documents how to use unwrapping to access the Snowflake-specific methods, then describes three of the situations in which you might need to unwrap:
Uploading data files directly from a stream to an internal stage.
Downloading data files directly from an internal stage to a stream.
Unwrapping Snowflake-specific classes¶
The Snowflake JDBC driver supports Snowflake-specific methods. These methods are defined in Snowflake-specific
Java-language interfaces, such as SnowflakeConnection, SnowflakeStatement, and SnowflakeResultSet. For example,
the SnowflakeStatement interface contains a getQueryID()
method that is not in the JDBC Statement interface.
When the Snowflake JDBC driver is asked to create a JDBC object (e.g. create a JDBC Statement
object by
calling a Connection
object’s createStatement()
method), the Snowflake JDBC driver actually creates
Snowflake-specific objects that implement not only the methods of the JDBC standard, but also the additional methods
from the Snowflake interfaces.
To access these Snowflake methods, you “unwrap” an object (such as a Statement
object) to expose the Snowflake
object and its methods. You can then call the additional methods.
The following code shows how to unwrap a JDBC Statement
object to expose the methods of the
SnowflakeStatement
interface, and then call one of those methods, in this case setParameter
:
Statement statement1; ... // Unwrap the statement1 object to expose the SnowflakeStatement object, and call the // SnowflakeStatement object's setParameter() method. statement1.unwrap(SnowflakeStatement.class).setParameter(...);
Performing an asynchronous query¶
The Snowflake JDBC Driver supports asynchronous queries (i.e. queries that return control to the user before the query completes). Users can start a query, then use polling to determine when the query has completed. After the query completes, the user can read the result set.
This feature allows a client program to run multiple queries in parallel without the client program itself using multi-threading.
Asynchronous queries use methods added to the SnowflakeConnection
, SnowflakeStatement
, SnowflakePreparedStatement
, and
SnowflakeResultSet
classes.
Note
To perform asynchronous queries, you must ensure the ABORT_DETACHED_QUERY
configuration parameter is FALSE
(default value).
If the connection to client is lost:
For synchronous queries, all in-progress synchronous queries are aborted immediately regardless of the parameter value.
For asynchronous queries:
If ABORT_DETACHED_QUERY is set to
FALSE
, in-progress asynchronous queries continue to run until they end normally.If ABORT_DETACHED_QUERY is set to
TRUE
, Snowflake automatically aborts all in-progress asynchronous queries when a client connection is not re-established after five minutes.
You can run a mix of synchronous and asynchronous queries in the same session.
Best practices for asynchronous queries¶
Ensure that you know which queries are dependent upon other queries before you run any queries in parallel. Some queries are interdependent and order sensitive, and therefore not suitable for parallelizing. For example, obviously an INSERT statement should not start until after the corresponding CREATE TABLE statement has finished.
Ensure that you do not run too many queries for the memory that you have available. Running multiple queries in parallel typically consumes more memory, especially if more than one ResultSet is stored in memory at the same time.
When polling, handle the rare cases where a query does not succeed. For example, avoid the following potential infinite loop:
QueryStatus queryStatus = QueryStatus.RUNNING; while (queryStatus != QueryStatus.SUCCESS) { // NOT RECOMMENDED Thread.sleep(2000); // 2000 milliseconds. queryStatus = resultSet.unwrap(SnowflakeResultSet.class).getStatus(); }
Instead, use code similar to the following:
// Assume that the query is not done yet. QueryStatus queryStatus = QueryStatus.RUNNING; while (queryStatus == QueryStatus.RUNNING || queryStatus == QueryStatus.RESUMING_WAREHOUSE) { Thread.sleep(2000); // 2000 milliseconds. queryStatus = resultSet.unwrap(SnowflakeResultSet.class).getStatus(); } if (queryStatus == QueryStatus.SUCCESS) { ... }
Ensure that transaction control statements (BEGIN, COMMIT, and ROLLBACK) do not execute in parallel with other statements.
Examples of asynchronous queries¶
Most of these examples require that the program import classes as shown below:
import java.sql.Connection; import java.sql.ResultSet; import java.sql.Statement; import net.snowflake.client.core.QueryStatus; import net.snowflake.client.jdbc.SnowflakeConnection; import net.snowflake.client.jdbc.SnowflakeResultSet; import net.snowflake.client.jdbc.SnowflakeStatement;
This is a very simple example:
String sql_command = ""; ResultSet resultSet; System.out.println("Create JDBC statement."); Statement statement = connection.createStatement(); sql_command = "SELECT PI()"; System.out.println("Simple SELECT query: " + sql_command); resultSet = statement.unwrap(SnowflakeStatement.class).executeAsyncQuery(sql_command); // Assume that the query isn't done yet. QueryStatus queryStatus = QueryStatus.RUNNING; while (queryStatus == QueryStatus.RUNNING || queryStatus == QueryStatus.RESUMING_WAREHOUSE) { Thread.sleep(2000); // 2000 milliseconds. queryStatus = resultSet.unwrap(SnowflakeResultSet.class).getStatus(); } if (queryStatus == QueryStatus.FAILED_WITH_ERROR) { // Print the error code to stdout System.out.format("Error code: %d%n", queryStatus.getErrorCode()); System.out.format("Error message: %s%n", queryStatus.getErrorMessage()); } else if (queryStatus != QueryStatus.SUCCESS) { System.out.println("ERROR: unexpected QueryStatus: " + queryStatus); } else { boolean result_exists = resultSet.next(); if (!result_exists) { System.out.println("ERROR: No rows returned."); } else { float pi_result = resultSet.getFloat(1); System.out.println("pi = " + pi_result); } }
This example stores the query ID, closes the connection, re-opens the connection, and uses the query ID to retrieve the data:
String sql_command = ""; ResultSet resultSet; String queryID = ""; System.out.println("Create JDBC statement."); Statement statement = connection.createStatement(); sql_command = "SELECT PI() * 2"; System.out.println("Simple SELECT query: " + sql_command); resultSet = statement.unwrap(SnowflakeStatement.class).executeAsyncQuery(sql_command); queryID = resultSet.unwrap(SnowflakeResultSet.class).getQueryID(); System.out.println("INFO: Closing statement."); statement.close(); System.out.println("INFO: Closing connection."); connection.close(); System.out.println("INFO: Re-opening connection."); connection = create_connection(args); use_warehouse_db_and_schema(connection); resultSet = connection.unwrap(SnowflakeConnection.class).createResultSet(queryID); // Assume that the query isn't done yet. QueryStatus queryStatus = QueryStatus.RUNNING; while (queryStatus == QueryStatus.RUNNING) { Thread.sleep(2000); // 2000 milliseconds. queryStatus = resultSet.unwrap(SnowflakeResultSet.class).getStatus(); } if (queryStatus == QueryStatus.FAILED_WITH_ERROR) { System.out.format( "ERROR %d: %s%n", queryStatus.getErrorMessage(), queryStatus.getErrorCode()); } else if (queryStatus != QueryStatus.SUCCESS) { System.out.println("ERROR: unexpected QueryStatus: " + queryStatus); } else { boolean result_exists = resultSet.next(); if (!result_exists) { System.out.println("ERROR: No rows returned."); } else { float pi_result = resultSet.getFloat(1); System.out.println("pi = " + pi_result); } }
Upload data files directly from a stream to an internal stage¶
You can upload data files using the PUT command. However, sometimes it makes sense to transfer data directly from a
stream to an internal (i.e. Snowflake) stage as a file. (The stage
can be any internal stage type: table stage, user stage, or named stage. The JDBC driver does not support uploading to an external
stage.) Here is the method exposed in the SnowflakeConnection
class:
/** * Method to compress data from a stream and upload it at a stage location. * The data will be uploaded as one file. No splitting is done in this method. * * Caller is responsible for releasing the inputStream after the method is * called. * * @param stageName stage name: e.g. ~ or table name or stage name * @param destPrefix path / prefix under which the data should be uploaded on the stage * @param inputStream input stream from which the data will be uploaded * @param destFileName destination file name to use * @param compressData compress data or not before uploading stream * @throws java.sql.SQLException failed to compress and put data from a stream at stage */ public void uploadStream(String stageName, String destPrefix, InputStream inputStream, String destFileName, boolean compressData) throws SQLException
Sample usage:
Connection connection = DriverManager.getConnection(url, prop); File file = new File("/tmp/test.csv"); FileInputStream fileInputStream = new FileInputStream(file); // upload file stream to user stage connection.unwrap(SnowflakeConnection.class).uploadStream("MYSTAGE", "testUploadStream", fileInputStream, "destFile.csv", true);
Code written for JDBC Driver versions prior to 3.9.2 might cast SnowflakeConnectionV1
rather than
unwrap SnowflakeConnection.class
. For example:
... // For versions prior to 3.9.2: // upload file stream to user stage ((SnowflakeConnectionV1) connection.uploadStream("MYSTAGE", "testUploadStream", fileInputStream, "destFile.csv", true));
Note
Customers using newer versions of the driver should update their code to use unwrap
.
Download data files directly from an internal stage to a stream¶
You can download data files using the GET command. However, sometimes it makes sense to transfer data directly from a
file in an internal (i.e. Snowflake) stage to a stream. (The stage
can be any internal stage type: table stage, user stage, or named stage. The JDBC driver does not support downloading to an
external stage.) Here is the method exposed in the SnowflakeConnection
class:
/** * Download file from the given stage and return an input stream * * @param stageName stage name * @param sourceFileName file path in stage * @param decompress true if file compressed * @return an input stream * @throws SnowflakeSQLException if any SQL error occurs. */ InputStream downloadStream(String stageName, String sourceFileName, boolean decompress) throws SQLException;
Sample usage:
Connection connection = DriverManager.getConnection(url, prop); InputStream out = connection.unwrap(SnowflakeConnection.class).downloadStream( "~", DEST_PREFIX + "/" + TEST_DATA_FILE + ".gz", true);
Code written for JDBC Driver versions prior to 3.9.2 might cast SnowflakeConnectionV1
rather than
unwrap SnowflakeConnection.class
. For example:
... // For versions prior to 3.9.2: // download file stream to user stage ((SnowflakeConnectionV1) connection.downloadStream(...));
Multi-statement support¶
This section describes how to execute multiple statements in a single request using the JDBC Driver.
Note
Executing multiple statements in a single query requires that a valid warehouse is available in a session.
By default, Snowflake returns an error for queries issued with multiple statements to protect against SQL injection . Executing multiple statements in a single query increases the risk of SQL injection. Snowflake recommends using it sparingly. To reduce the SQL injection risk, use the
SnowflakeStatement
class’ssetParameter()
method to specify the number of statements to be executed, which makes it more difficult to inject a statement by appending it. For more information aboutSnowflakeStatement
, see Interface: SnowflakeStatement.
Sending multiple statements and handling results¶
Queries containing multiple statements can be executed the same way as queries with a single statement, except that the query string contains multiple statements separated by semicolons.
There are two ways to allow multiple statements:
Call Statement.setParameter(“MULTI_STATEMENT_COUNT”, n) to specify how many statements at a time this Statement should be allowed to execute. See below for more details.
Set the MULTI_STATEMENT_COUNT parameter at the session level or the account level by executing one of the following commands:
alter session set MULTI_STATEMENT_COUNT = 0;
Or:
alter account set MULTI_STATEMENT_COUNT = 0;
Setting the parameter to 0 allows an unlimited number of statements. Setting the parameter to 1 allows only one statement at a time.
In order to make SQL Injection attacks more difficult, users can call the setParameter
method to
specify the number of statements to be executed in a single call, as shown below.
In this example, the number of statements to execute in a single call is 3:
// Specify the number of statements that we expect to execute. statement.unwrap(SnowflakeStatement.class).setParameter( "MULTI_STATEMENT_COUNT", 3);
The default number of statements is 1; in other words, multi-statement mode is off.
To execute multiple statements without specifying the exact number, pass a value of 0.
The MULTI_STATEMENT_COUNT parameter is not part of the JDBC standard; it is a Snowflake extension. This parameter affects more than one Snowflake driver/connector.
When multiple statements are executed in a single execute()
call, the result of the first statement is
available through the standard getResultSet()
and getUpdateCount()
methods.
To access the results of the statements that follow, use the getMoreResults()
method.
This method returns true
when more statements are available for iteration, and false
otherwise.
The example below sets the MULTI_STATEMENT_COUNT parameter, executes 3 statements, and retrieves update counts and result sets:
// Create a string that contains multiple SQL statements. String command_string = "create table test(n int); " + "insert into test values (1), (2); " + "select * from test order by n"; Statement stmt = connection.createStatement(); // Specify the number of statements (3) that we expect to execute. stmt.unwrap(SnowflakeStatement.class).setParameter( "MULTI_STATEMENT_COUNT", 3); // Execute all of the statements. stmt.execute(command_string); // false // --- Get results. --- // First statement (create table) stmt.getUpdateCount(); // 0 (DDL) // Second statement (insert) stmt.getMoreResults(); // true stmt.getUpdateCount(); // 2 // Third statement (select) stmt.getMoreResults(); // true ResultSet rs = stmt.getResultSet(); rs.next(); // true rs.getInt(1); // 1 rs.next(); // true rs.getInt(1); // 2 rs.next(); // false // Past the last statement executed. stmt.getMoreResults(); // false stmt.getUpdateCount(); // 0 (no more results)
Snowflake recommends using execute()
for multi-statement queries.
The methods executeQuery()
and executeUpdate()
also support multiple statements, but will throw an exception if the first result is not the expected result type (result set and update count, respectively).
Failed statements¶
If any of the SQL statements fails to compile or execute, execution is aborted. Any previous statements that ran before are unaffected.
For example, if the statements below are run as a single multi-statement query, the query will fail on the third statement, and an exception will be thrown.
CREATE OR REPLACE TABLE test(n int); INSERT INTO TEST VALUES (1), (2); INSERT INTO TEST VALUES ('not_an_int'); -- execution fails here INSERT INTO TEST VALUES (3);
If you were to then query the contents of table test
, values 1
and 2
would be present.
Unsupported features¶
PUT and GET statements are not supported for multi-statement queries.
Preparing statements and using bind variables are also not supported for multi-statement queries.
Binding variables to statements¶
Binding allows a SQL statement to use a value that is stored in a Java variable.
Simple binding¶
Without binding, a SQL statement specifies values by specifying literals inside the statement. For example, the following
statement uses the literal value 42
in an UPDATE statement:
stmt.execute("UPDATE table1 SET integer_column = 42 WHERE ID = 1000");
With binding, you can execute a SQL statement that uses a value that is inside a variable. For example:
int my_integer_variable = 42; PreparedStatement pstmt = connection.prepareStatement("UPDATE table1 SET integer_colum = ? WHERE ID = 1000"); pstmt.setInt(1, my_integer_variable); pstmt.executeUpdate();
The ?
inside the VALUES
clause specifies that the SQL statement uses the value from a variable. The setInt()
method
specifies that the first question mark in the SQL statement should be replaced with the value in the variable named
my_integer_variable
. Note that setInt()
uses 1-based, rather than 0-based values (i.e. the first question mark is
referenced by 1, not 0).
Binding variables to timestamp columns¶
Snowflake supports three different variations for timestamps: TIMESTAMP_LTZ , TIMESTAMP_NTZ , TIMESTAMP_TZ. When you call
PreparedStatement.setTimestamp
to bind a variable to a timestamp column, the JDBC Driver interprets the timestamp value in
terms of the local time zone (TIMESTAMP_LTZ
) or the time zone of the Calendar
object passed in as an argument:
// The following call interprets the timestamp in terms of the local time zone.
insertStmt.setTimestamp(1, myTimestamp);
// The following call interprets the timestamp in terms of the time zone of the Calendar object.
insertStmt.setTimestamp(1, myTimestamp, Calendar.getInstance(TimeZone.getTimeZone("America/New_York")));
If you want the driver to interpret the timestamp using a different variation (e.g. TIMESTAMP_NTZ
), use one of the
following approaches:
Set the session parameter CLIENT_TIMESTAMP_TYPE_MAPPING to the variation.
Note that the parameter affects all binding operations for the current session. If you need to change the variation (e.g. back to
TIMESTAMP_LTZ
), you must set this session parameter again.(In the JDBC Driver 3.13.3 and later versions) Call the
PreparedStatement.setObject
method, and use thetargetSqlType
parameter to specify one of the following Snowflake timestamp variations:SnowflakeUtil.EXTRA_TYPES_TIMESTAMP_LTZ
SnowflakeUtil.EXTRA_TYPES_TIMESTAMP_TZ
SnowflakeUtil.EXTRA_TYPES_TIMESTAMP_NTZ
For example:
import net.snowflake.client.jdbc.SnowflakeUtil; ... insertStmt.setObject(1, myTimestamp, SnowflakeUtil.EXTRA_TYPES_TIMESTAMP_NTZ);
Batch inserts¶
In your Java application code, you can insert multiple rows in a single batch by binding parameters in an INSERT statement and
calling addBatch()
and executeBatch()
.
As an example, the following code inserts two rows into a table that contains an INTEGER column and a VARCHAR column. The example
binds values to the parameters in the INSERT statement and calls addBatch()
and executeBatch()
to perform a batch
insert.
Connection connection = DriverManager.getConnection(url, prop); connection.setAutoCommit(false); PreparedStatement pstmt = connection.prepareStatement("INSERT INTO t(c1, c2) VALUES(?, ?)"); pstmt.setInt(1, 101); pstmt.setString(2, "test1"); pstmt.addBatch(); pstmt.setInt(1, 102); pstmt.setString(2, "test2"); pstmt.addBatch(); int[] count = pstmt.executeBatch(); // After execution, count[0]=1, count[1]=1 connection.commit();
When you use this technique to insert a large number of values, the driver can improve performance by streaming the data (without creating files on the local machine) to a temporary stage for ingestion. The driver automatically does this when the number of values exceeds a threshold.
In addition, the current database and schema for the session must be set. If these are not set, the CREATE TEMPORARY STAGE command executed by the driver can fail with the following error:
CREATE TEMPORARY STAGE SYSTEM$BIND file_format=(type=csv field_optionally_enclosed_by='"')
Cannot perform CREATE STAGE. This session does not have a current schema. Call 'USE SCHEMA', or use a qualified name.
Note
For alternative ways to load data into the Snowflake database (including bulk loading using the COPY command), see Load Data into Snowflake.
Java sample program¶
For a working sample written in Java, right-click the name of the file, SnowflakeJDBCExample.java
, and save the link/file to your local file system.
Troubleshooting¶
I/O error: Connection reset¶
In some cases, the JDBC Driver might fail with the following error message after a period of inactivity:
I/O error: Connection reset
You can work around the problem by setting a specific “time to live” for the connections. If a connection is idle for longer than the “time to live”, the JDBC Driver removes the connection from the connection pool and creates a new connection.
To set the time to live, set the Java system property named net.snowflake.jdbc.ttl
to the number of seconds that the
connection should live:
To set this property programmatically, call
System.setProperty
:// Set the "time to live" to 60 seconds. System.setProperty("net.snowflake.jdbc.ttl", "60")
To set this property when running the
java
command, use the-D
flag:# Set the "time to live" to 60 seconds. java -cp .:snowflake-jdbc-<version>.jar -Dnet.snowflake.jdbc.ttl=60 <ClassName>
The default value of the net.snowflake.jdbc.ttl
property is -1
, which means that idle connections are not removed from
the connection pool.
Handling errors¶
When handling errors and exceptions for a JDBC application, you can use the ErrorCode.java file that Snowflake provides to determine the cause of the problems. Error codes specific to the JDBC driver start with 2, in the form: 2NNNNN.
Note
The link to the ErrorCode.java in the public snowflake-jdbc git repository points to the latest version of the file, which might differ from the version of the JDBC driver you currently use.