Lookup UDF Join

Lookup UDF is used to get dimension data via primary key from a dimension table allowing a decoration join functionality. Lookup UDF can only be used with a dimension table in Pinot.

Syntax

The UDF function syntax is listed as below:

lookupUDFSpec:
    LOOKUP
    '('
    '''dimTable'''
    '''dimColToLookup'''
    [ '''dimJoinKey''', factJoinKey ]*
    ')'

• dimTable Name of the dim table to perform the lookup on.

• dimColToLookUp The column name of the dim table to be retrieved to decorate our result.

• dimJoinKey The column name on which we want to perform the lookup i.e. the join column name for dim table.

• factJoinKey The column name on which we want to perform the lookup against e.g. the join column name for fact table

Noted that:

1. all the dim-table-related expressions are expressed as literal strings, this is the LOOKUP UDF syntax limitation: we cannot express column identifier which doesn't exist in the query's main table, which is the factTable table.

2. the syntax definition of [ '''dimJoinKey''', factJoinKey ]* indicates that if there are multiple dim partition columns, there should be multiple join key pair expressed.

Examples

Here are some of the examples

Single-partition-key-column Example

Consider the table baseballStats

and dim table dimBaseballTeams

several acceptable queries are:

Dim-Fact LOOKUP example

SELECT 
  playerName, 
  teamID, 
  LOOKUP('dimBaseballTeams', 'teamName', 'teamID', teamID) AS teamName, 
  LOOKUP('dimBaseballTeams', 'teamAddress', 'teamID', teamID) AS teamAddress
FROM baseballStats 

Self LOOKUP example

SELECT 
  teamID, 
  teamName AS nameFromLocal,
  LOOKUP('dimBaseballTeams', 'teamName', 'teamID', teamID) AS nameFromLookup
FROM dimBaseballTeams

Complex-partition-key-columns Example

Consider a single dimension table with schema:

BILLING SCHEMA

Self LOOKUP example

select 
  customerId,
  missedPayment, 
  LOOKUP('billing', 'city', 'customerId', customerId, 'creditHistory', creditHistory) AS lookedupCity 
from billing

Usage FAQ

• The data return type of the UDF will be that of the dimColToLookUp column type.

• when multiple primary key columns are used for the dimension table (e.g. composite primary key), ensure that the order of keys appearing in the lookup() UDF is the same as the order defined in the primaryKeyColumns from the dimension table schema.