How to get item count from DynamoDB?

Can be seen from UI as well. Go to overview tab on table, you will see item count. Hope it helps someone.

You can use the Select parameter and use COUNT in the request. It "returns the number of matching items, rather than the matching items themselves". Important, as brought up by Saumitra R. Bhave in a comment, "If the size of the Query result set is larger than 1 MB, then ScannedCount and Count will represent only a partial count of the total items. You will need to perform multiple Query operations in order to retrieve all of the results".

I'm Not familiar with PHP but here is how you could use it with Java. And then instead of using Count (which I am guessing is a function in PHP) on the 'Items' you can use the Count value from the response - $result['Count']:

final String week = "whatever";
final Integer myPoint = 1337;
Condition weekCondition = new Condition()
        .withComparisonOperator(ComparisonOperator.EQ)
        .withAttributeValueList(new AttributeValue().withS(week));
Condition myPointCondition = new Condition()
        .withComparisonOperator(ComparisonOperator.GE)
        .withAttributeValueList(new AttributeValue().withN(myPoint.toString()))

Map<String, Condition> keyConditions = new HashMap<>();
keyConditions.put("week", weekCondition);
keyConditions.put("point", myPointCondition);

QueryRequest request = new QueryRequest("game_table");
request.setIndexName("week-point-index");
request.setSelect(Select.COUNT);
request.setKeyConditions(keyConditions);

QueryResult result = dynamoDBClient.query(request);
Integer count = result.getCount();

If you don't need to emulate the WHERE clause, you can use a DescribeTable request and use the resulting item count to get an estimate.

The number of items in the specified table. DynamoDB updates this value approximately every six hours. Recent changes might not be reflected in this value.

Also, an important note from the documentation as noted by Saumitra R. Bhave in the comments on this answer:

If the size of the Query result set is larger than 1 MB, ScannedCount and Count represent only a partial count of the total items. You need to perform multiple Query operations to retrieve all the results (see Paginating Table Query Results).

With the aws dynamodb cli you can get it via scan as follows:

aws dynamodb scan --table-name <TABLE_NAME> --select "COUNT"

The response will look similar to this:

{
    "Count": 123,
    "ScannedCount": 123,
    "ConsumedCapacity": null
}

notice that this information is in real time in contrast to the describe-table api