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# Chapter 51. Joiners

Joiners serve to join data from more data sources according to the key values.

We can distinguish Joiners according to how they process data. Most Joiners work using key values.

- Some Joiners read data from two or more input ports and join them according to the equality of key values.

  - ExtHashJoin joins two or more data inputs according to the equality of key values.

  - ExtMergeJoin joins two or more sorted data inputs according to the equality of key values.

- Other Joiners read data from one input port and another data source and join them according to the equality of key values.

  - DBJoin joins one input data source and a database according to the equality of key values.

  - LookupJoin joins one input data source and a lookup table according to the equality of key values.

- One Joiner joins data according to the user-defined relation of key values.

  - RelationalJoin joins two or more sorted data inputs according to the user-defined relation of key values (`!=`, `>`, `>=`, `<`. `<=`).

- Combine joins data flows by tuples.

- CrossJoin creates a Cartesian product of records from connected input ports.

##### See also

Chapter 30, Components
Common Properties of Components
Specific Attribute Types
Common Properties of Joiners
Chapter 50, Transformers

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