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datastream = DATABASESOURCE({connection='con1', table='main'})

This query tries to fetch the schema from the table main. If the schema in a MySQL has, for example, the attributes "id, value" with the datatypes "int, varchar", this is mapped to an output schema "id, value" with the datatypes "integer, string" in Odysseus. If a database has a special data type that is not known by JDBC (see java.sql.Types), it is mapped to the Odysseus datatype called "Object". Since the fetching of the schema from the database opens a connection, you can explicitely define the schema alternatively by using the optional "attributes" paramter here:

datastream = DATABASESOURCE({connection='con1', table='main', attributes=[['id', 'INTEGER'],['val', 'STRING']]})

Since PQL allows to create views and names for reusing connections (see The Odysseus Procedural Query Language (PQL) - Usage and Development), you may use this syntax, for example to create a dedicated source entry.

datastream := DATABASESOURCE({connection='con1', table='main'})

Then you can use this in other queries, like in the following example:

example = PROJECT({attributes=['val']}, datastream)

Remember the special behevior, if you reuse an existing operator. If there is already an operator that reads from the database, a second operator would join this reading - and not beginning from the start of the table.

Writing to a database

You can write a stream into a database by using the DATABASESINK operator. So, if you have for example a stream or an operator that is named "datastream", the DATABASESINK can be used as follows:

result = DATABASESINK({connection='con1', table='main'}, datastream)

Using a connection in StreamSQL (CQL)

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