以前から気になっていたが、APIGatewayをトリガーにLambda関数を動かしているのにeventが取得できなく・・・調べたところ
リクエストのマッピングテンプレートを使わない場合、[Lambdaプロキシ統合の使用]にチェックしないとeventが空になってしまうんですね。

・APIGatewayはエンドポイントをリージョンとしたシンプルなものAPIGateway/Lambda関数の呼び出し辺りを参考に作成
・Lambda関数は下記のコードで、APIGatewayからのeventをそのままブラウザに表示しています。

import json
  
def lambda_handler(event, context):
    jsn_str = json.dumps(event, ensure_ascii=False, indent=2)
    return {
        'isBase64Encoded': False,
        'statusCode': 200,
        'headers': {},
        'body': jsn_str
    }

※Lambda関数選択時に、[Lambdaプロキシ統合の使用]をチェックしません。

ブラウザへのレスポンス

{"isBase64Encoded": false, "statusCode": 200, "headers": {}, "body": "{}"}

※Lambda関数選択時に、[Lambdaプロキシ統合の使用]をチェックします。

ブラウザへのレスポンスは長いので末尾に

[https://XXXXX.execute-api.ap-northeast-1.amazonaws.com/test]の末尾に[?id=0001&value=tokyo]をつけてリクエストしてみる。
[queryStringParameters]と[multiValueQueryStringParameters]が追加されていました。

  "queryStringParameters": {
    "id": "0001",
    "value": "tokyo"
  },
  "multiValueQueryStringParameters": {
    "id": [
      "0001"
    ],
    "value": [
      "tokyo"
    ]
  }

Aws/Lambda/APIGWのクエリパラメータをDyanmoDBに書き込む

{
  "resource": "/",
  "path": "/",
  "httpMethod": "GET",
  "headers": {
    "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9",
    "accept-encoding": "gzip, deflate, br",
    "accept-language": "ja",
    "cache-control": "max-age=0",
    "Host": "{APIGWのID}.execute-api.ap-northeast-1.amazonaws.com",
    "referer": "https://ap-northeast-1.console.aws.amazon.com/",
    "sec-ch-ua": "\" Not A;Brand\";v=\"99\", \"Chromium\";v=\"90\", \"Google Chrome\";v=\"90\"",
    "sec-ch-ua-mobile": "?0",
    "sec-fetch-dest": "document",
    "sec-fetch-mode": "navigate",
    "sec-fetch-site": "cross-site",
    "sec-fetch-user": "?1",
    "upgrade-insecure-requests": "1",
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36",
    "X-Amzn-Trace-Id": "Root=1-60aa083e-2598a84640ebc8667f9f08ee",
    "X-Forwarded-For": "{接続元IPアドレス}",
    "X-Forwarded-Port": "443",
    "X-Forwarded-Proto": "https"
  },
  "multiValueHeaders": {
    "accept": [
      "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9"
    ],
    "accept-encoding": [
      "gzip, deflate, br"
    ],
    "accept-language": [
      "ja"
    ],
    "cache-control": [
      "max-age=0"
    ],
    "Host": [
      "{APIGWのID}.execute-api.ap-northeast-1.amazonaws.com"
    ],
    "referer": [
      "https://ap-northeast-1.console.aws.amazon.com/"
    ],
    "sec-ch-ua": [
      "\" Not A;Brand\";v=\"99\", \"Chromium\";v=\"90\", \"Google Chrome\";v=\"90\""
    ],
    "sec-ch-ua-mobile": [
      "?0"
    ],
    "sec-fetch-dest": [
      "document"
    ],
    "sec-fetch-mode": [
      "navigate"
    ],
    "sec-fetch-site": [
      "cross-site"
    ],
    "sec-fetch-user": [
      "?1"
    ],
    "upgrade-insecure-requests": [
      "1"
    ],
    "User-Agent": [
      "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36"
    ],
    "X-Amzn-Trace-Id": [
      "Root=1-60aa083e-2598a84640ebc8667f9f08ee"
    ],
    "X-Forwarded-For": [
      "{接続元IPアドレス}"
    ],
    "X-Forwarded-Port": [
      "443"
    ],
    "X-Forwarded-Proto": [
      "https"
    ]
  },
  "queryStringParameters": null,
  "multiValueQueryStringParameters": null,
  "pathParameters": null,
  "stageVariables": null,
  "requestContext": {
    "resourceId": "sk5324ywjb",
    "resourcePath": "/",
    "httpMethod": "GET",
    "extendedRequestId": "fxY5tHljtjMFq3w=",
    "requestTime": "23/May/2021:07:46:06 +0000",
    "path": "/test",
    "accountId": "{アカウントID}",
    "protocol": "HTTP/1.1",
    "stage": "test",
    "domainPrefix": "{APIGWのID}",
    "requestTimeEpoch": 1621755966012,
    "requestId": "e00c2936-dca1-4084-a574-a7c8b7fb4b21",
    "identity": {
      "cognitoIdentityPoolId": null,
      "accountId": null,
      "cognitoIdentityId": null,
      "caller": null,
      "sourceIp": "{接続元IPアドレス}",
      "principalOrgId": null,
      "accessKey": null,
      "cognitoAuthenticationType": null,
      "cognitoAuthenticationProvider": null,
      "userArn": null,
      "userAgent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36",
      "user": null
    },
    "domainName": "{APIGWのID}.execute-api.ap-northeast-1.amazonaws.com",
    "apiId": "{APIGWのID}"
  },
  "body": null,
  "isBase64Encoded": false
}