COUNT function in Amazon QLDB - Amazon Quantum Ledger Database (Amazon QLDB)

COUNT function in Amazon QLDB

In Amazon QLDB, use the COUNT function to return the number of documents that are defined by the given expression. This function has two variations:

  • COUNT(*) – Counts all of the documents in the target table whether or not they include null or missing values.

  • COUNT(expression) – Computes the number of documents with non-null values in a specific, existing field or expression.


The COUNT function is not optimized, so we don't recommend using it without an indexed lookup. When you run a query in QLDB without an indexed lookup, it invokes a full table scan. This can cause performance problems on large tables, including concurrency conflicts and transaction timeouts.

To avoid table scans, you must run statements with a WHERE predicate clause using an equality operator (= or IN) on an indexed field or a document ID. For more information, see Optimizing query performance.


COUNT ( * | expression )



The field name or expression that the function operates on. This parameter can be any of the supported Data types.

Return type



SELECT COUNT(*) FROM VehicleRegistration r WHERE r.LicensePlateNumber = 'CA762X' -- 1 SELECT COUNT(r.VIN) FROM Vehicle r WHERE r.VIN = '1N4AL11D75C109151' -- 1 SELECT COUNT(a) FROM << { 'a' : 1 }, { 'a': 2 }, { 'a': 3 } >> -- 3

Related functions