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Custom SQL Functions

The SQL Engine can extend the SQL functions' set, defined by the ANSI-99 specification, via the addition of custom SQL functions written in Java.

A custom SQL function is just a public or public static method marked by the @QuerySqlFunction annotation.

static class SqlFunctions {
    @QuerySqlFunction
    public static int sqr(int x) {
        return x * x;
    }
}

The class that owns the custom SQL function has to be registered in the CacheConfiguration. To do that, use the setSqlFunctionClasses(…) method.

// Preparing a cache configuration.
CacheConfiguration cfg = new CacheConfiguration("myCache");

// Registering the class that contains custom SQL functions.
cfg.setSqlFunctionClasses(SqlFunctions.class);

IgniteCache cache = ignite.createCache(cfg);

Once you have deployed a cache with the above configuration, you can call the custom function from within SQL queries:

// Preparing the query that uses the custom defined 'sqr' function.
SqlFieldsQuery query = new SqlFieldsQuery("SELECT name FROM myCache WHERE sqr(size) > 100");

// Executing the query.
cache.query(query).getAll();

Custom SQL function can be a table function. Result of table function is treated as a row set (a table) and can be used by other SQL operators. Custom SQL function is also a public or public static method marked by annotation @QuerySqlTableFunction. Table function must return an Iterable as a row set. Each row can be represented by an Object[] or by a Collection. Row length must match the defined number of column types. Row value types must match the defined column types or be able assigned to them.

static class SqlTableFunctions {
    @QuerySqlTableFunction(columnTypes = {Integer.class, String.class}, columnNames = {"INT_COL", "STR_COL"})
    public static Iterable<Object[]> table_function(int i) {
        return Arrays.asList(
            new Object[] {i, "" + i},
            new Object[] {i * 10, "empty"}
        );
    }
}

CacheConfiguration cfg = new CacheConfiguration("myCache");

cfg.setSqlFunctionClasses(SqlTableFunctions.class);

IgniteCache cache = ignite.createCache(cfg);

SqlFieldsQuery query = new SqlFieldsQuery("SELECT STR_COL FROM TABLE_FUNCTION(10) WHERE INT_COL > 50");

cache.query(query).getAll();

With custom SQL function you can get access to application attributes set on the client side via SessionContext API.

Note	Creating custom functions in the system schema is forbidden. Creating a custom function in schema 'PUBLIC' is forbidden if the function name interferes with a standard function like 'TYPEOF' or 'SUBSTRING'.

Note	The table functions and application attributes are currently available only with Calcite.

Note

With Calcite, a custom SQL function can execute nested SQL queries through Ignite APIs such as SqlFieldsQuery only when the blocking query task executor is enabled with the -DIGNITE_CALCITE_USE_QUERY_BLOCKING_TASK_EXECUTOR=true system property. The default striped query task executor can lead to deadlocks for queries started from user-defined functions.

Note	When nested SQL queries are executed from user-defined functions, configure `IgniteConfiguration.QueryThreadPoolSize` so it is greater than the maximum number of concurrent queries initiated from UDFs. Otherwise, nested queries can fail because of query thread pool starvation.

Note	Classes registered with `CacheConfiguration.setSqlFunctionClasses(…)` must be added to the classpath of all the nodes where the defined custom functions might be executed. Otherwise, you will get a `ClassNotFoundException` error when trying to execute the custom function.

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