# Providing Parameters from a Database

The DatabaseParameterProvider at its core maps database rows to Parameters, specified by a Parameter Name Column and Parameter Value Column. The Parameter Group name must also be accounted for, and may be specified in different ways using the Parameter Grouping Strategy.

Before discussing the actual configuration, note that in some databases, the words 'PARAMETER', 'PARAMETERS', 'GROUP', and even 'VALUE' are reserved words. If you choose a column name that is a reserved word in the database you are using, make sure to quote it per the database documentation.

Also note that you should use the preferred table name and column name case for your database. For example, Postgres prefers lowercase table and column names, while Oracle prefers capitalized ones. Choosing the appropriate case can avoid unexpected issues in configuring your DatabaseParameterProvider.

The default configuration uses a fully column-based approach, with the Parameter Group Name also specified by columns in the same table. An example of a table using this configuration would be:

PARAMETER_CONTEXTS
PARAMETER_NAME | PARAMETER_VALUE | PARAMETER_GROUP
--- | --- | ---
param.foo | value-foo | group_1
param.bar | value-bar | group_1
param.one | value-one | group_2
param.two | value-two | group_2
Table 1: Database table example with Grouping Strategy = Column

In order to use the data from this table, set the following Properties:

- Parameter Grouping Strategy - Column
- Table Name - PARAMETER_CONTEXTS
- Parameter Name Column - PARAMETER_NAME
- Parameter Value Column - PARAMETER_VALUE
- Parameter Group Name Column - PARAMETER_GROUP

Once fetched, the parameters in this example will look like this:

Parameter Group group_1:

- param.foo - value-foo
- param.bar - value-bar

Parameter Group group_2:

- param.one - value-one
- param.two - value-two

### Grouping Strategy

The default Grouping Strategy is by Column, which allows you to specify the parameter Group name explicitly in the Parameter Group Column. Note that if the value in this column is NULL, an exception will be thrown.

The other Grouping Strategy is by Table, which maps each table to a Parameter Group and sets the Parameter Group Name to the table name. In this Grouping Strategy, the Parameter Group Column is not used. An example configuration using this strategy would be:

- Parameter Grouping Strategy - Table
- Table Names - KAFKA, S3
- Parameter Name Column - PARAMETER_NAME
- Parameter Value Column - PARAMETER_VALUE

An example of some tables that may be used with this strategy:

KAFKA
PARAMETER_NAME | PARAMETER_VALUE
--- | ---
brokers | http://localhost:9092
topic | my-topic
password | my-password
Table 2: 'KAFKA' Database table example with Grouping Strategy = Table

S3
PARAMETER_NAME | PARAMETER_VALUE
--- | ---
bucket | my-bucket
secret.access.key | my-key
Table 3: 'S3' Database table example with Grouping Strategy = Table

Once fetched, the parameters in this example will look like this:

Parameter Group KAFKA:

- brokers - http://localhost:9092
- topic - my-topic
- password - my-password

Parameter Group S3:

- bucket - my-bucket
- secret.access.key - my-key

### Filtering rows

If you need to include only some rows in a table as parameters, you can use the 'SQL WHERE clause' property. An example of this is as follows:

- Parameter Grouping Strategy - Table
- Table Names - KAFKA, S3
- Parameter Name Column - PARAMETER_NAME
- Parameter Value Column - PARAMETER_VALUE
- SQL WHERE clause - OTHER_COLUMN = 'my-parameters'

Here we are assuming there is another column, 'OTHER_COLUMN' in both the KAFKA and S3 tables. Only rows whose 'OTHER_COLUMN' value is 'my-parameters' will then be fetched from these tables.