Case statements can be used for branching execution, like a switch statement.

Syntax:

CASE v WHEN t[1] THEN r[1] 
  WHEN t[2] THEN r[2] ... 
  WHEN t[n] THEN r[n] 
  ELSE r[e] END

The expression v is evaluated and matched for equality against the t[i] value of each WHEN clause. If a match is found, the corresponding r[i] expression becomes the result of the CASE statement. The WHEN clauses are evaluated in order so that if there's more than one matching clause, the result of the first matching clause becomes the result of the CASE statement. If there are no matches, r[e] of the ELSE clause is the result. If there's no match and no ELSE clause, the result is Undefined.

CASE statements require at least one WHEN clause. An ELSE clause is optional.

For example:

Incoming payload published on topic topic/subtopic:

{
    "color":"yellow"
} 

SQL statement:

SELECT CASE color
        WHEN 'green' THEN 'go'
        WHEN 'yellow' THEN 'caution'
        WHEN 'red' THEN 'stop'
        ELSE 'you are not at a stop light' END as instructions
    FROM 'topic/subtopic'

The resulting output payload would be:

{
    "instructions":"caution"
}