Efficient SQL test query or validation query that will work across all (or most) databases

Many database connection pooling libraries provide the ability to test their SQL connections for idleness. For example, the JDBC pooling library c3p0 has a property called preferredTestQuery, which gets executed on the connection at configured intervals. Similarly, Apache Commons DBCP has validationQuery.

Many example queries I've seen are for MySQL and recommend using SELECT 1; as the value for the test query. However, this query doesn't work on some databases (e.g. HSQLDB, for which SELECT 1 expects a FROM clause).

Is there a database-agnostic query that's equivalently efficient but will work for all SQL databases?

Edit:

If there's not (which seems to be the case), can somebody suggest a set of SQL queries that will work for various database providers? My intention would be to programmatically determine a statement I can use based on my database provider configuration.

Solution 1:

After a little bit of research along with help from some of the answers here:

SELECT 1

• H2
• MySQL
• Microsoft SQL Server (according to NimChimpsky)
• PostgreSQL
• SQLite
• Hive

SELECT 1 FROM DUAL

• Oracle

SELECT 1 FROM any_existing_table WHERE 1=0

or

SELECT 1 FROM INFORMATION_SCHEMA.SYSTEM_USERS

or

CALL NOW()

• HSQLDB (tested with version 1.8.0.10)

  Note: I tried using a WHERE 1=0 clause on the second query, but it didn't work as a value for Apache Commons DBCP's validationQuery, since the query doesn't return any rows

VALUES 1 or SELECT 1 FROM SYSIBM.SYSDUMMY1

• Apache Derby (via daiscog)

SELECT 1 FROM SYSIBM.SYSDUMMY1

• DB2

select count(*) from systables

• Informix

Solution 2:

If your driver is JDBC 4 compliant, there is no need for a dedicated query to test connections. Instead, there is Connection.isValid to test the connection.

JDBC 4 is part of Java 6 from 2006 and you driver should support this by now!

Famous connection pools, like HikariCP, still have a config parameter for specifying a test query but strongly discourage to use it:

🔠connectionTestQuery

If your driver supports JDBC4 we strongly recommend not setting this property. This is for "legacy" databases that do not support the JDBC4 Connection.isValid() API. This is the query that will be executed just before a connection is given to you from the pool to validate that the connection to the database is still alive. Again, try running the pool without this property, HikariCP will log an error if your driver is not JDBC4 compliant to let you know. Default: none

Solution 3:

Unfortunately there is no SELECT statement that will always work regardless of database.

Most databases support:

SELECT 1

Some databases don't support this but have a table called DUAL that you can use when you don't need a table:

SELECT 1 FROM DUAL

MySQL also supports this for compatibility reasons, but not all databases do. A workaround for databases that don't support either of the above is to create a table called DUAL that contains a single row, then the above will work.

HSQLDB supports neither of the above, so you can either create the DUAL table or else use:

SELECT 1 FROM any_table_that_you_know_exists_in_your_database