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LET operation in AQL

You can use the LET operation to assign an arbitrary value to a variable

The variable is introduced in the scope the LET statement is placed in. You cannot change the value once assigned.


LET variableName = expression

expression can be a simple expression or a subquery.

For allowed variable names AQL Syntax.


Variables are immutable in AQL, which means they cannot be re-assigned:

LET a = [1, 2, 3]  // initial assignment

a = PUSH(a, 4)     // syntax error, unexpected identifier
LET a = PUSH(a, 4) // parsing error, variable 'a' is assigned multiple times
LET b = PUSH(a, 4) // allowed, result: [1, 2, 3, 4]

LET statements are mostly used to declare complex computations and to avoid repeated computations of the same value at multiple parts of a query.

FOR u IN users
  LET numRecommendations = LENGTH(u.recommendations)
    "user" : u,
    "numRecommendations" : numRecommendations,
    "isPowerUser" : numRecommendations >= 10

In the above example, the computation of the number of recommendations is factored out using a LET statement, thus avoiding computing the value twice in the RETURN statement.

Another use case for LET is to declare a complex computation in a subquery, making the whole query more readable.

FOR u IN users
  LET friends = (
  FOR f IN friends 
    FILTER == f.userId
    RETURN f
  LET memberships = (
  FOR m IN memberships
    FILTER == m.userId
      RETURN m
    "user" : u, 
    "friends" : friends, 
    "numFriends" : LENGTH(friends), 
    "memberShips" : memberships 

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