Using the FROM clause
The FROM clause is used to iterate over an input element defined by an identifier.
The FROM clause should be structured as
follows:
FROM expression Information noteNote: The FROM clause can be used with an expression that returns
an array, a record or a primitive type. With a record or a primitive type, the clause
creates an array containing a single item.
The FROM clause can contain other keywords, such as AS and INDEX.
The AS keyword allows you to create an alias for an array, it can then be used to refer to the elements in the array in subsequent clauses. The alias must be unique throughout the query and should be defined as follows:FROM expression AS alias When
using a FROM clause without an alias, all identifiers used in the query
are treated as relative to the identifier in the FROM clause, except
when it is followed by an UNNEST clause or when the identifier is an
absolute path. For example, in the following query:
FROM customers
SELECT {
name,
id
}The elements selected are customers.name and
customers.id. You would get the same result with this query, where
the input data is named
input:
FROM customers
SELECT {
input.customers.name,
input.customers.id
}The INDEX keyword allows you to store the index of
the current iteration in a variable. The variable must start with the $
character and cannot be a hierarchical identifier, for example,
$item.index is not a valid variable. The variable must be unique
throughout the query. The INDEX should be defined as
follows:
FROM expression INDEX $variable_name The
following examples are valid FROM
clauses:
FROM customers AS c INDEX $iFROM 1 TO 5 AS iFROM toArray(address_1, address_2, address_3) AS addr INDEX $iFROM ['a', 'e', 'i', 'o', 'u', 'y' ] AS vowels