"Already exists" while pooling

Question

I start MySQL docker starts and run fine:

 docker run -d `
     --network todo-app --network-alias mysql `
     -v todo-mysql-data:/var/lib/mysql `
     -e MYSQL_ROOT_PASSWORD=secret `
     -e MYSQL_DATABASE=todos `
     mysql:5.7

But what does line 69692152171a: Already exists means? Command docker images brings nothing with id 69692152171a.

Unable to find image 'mysql:5.7' locally
5.7: Pulling from library/mysql
69692152171a: Already exists
1651b0be3df3: Pull complete
951da7386bc8: Pull complete
0f86c95aa242: Pull complete
37ba2d8bd4fe: Pull complete
6d278bb05e94: Pull complete
497efbd93a3e: Pull complete
a023ae82eef5: Pull complete
e76c35f20ee7: Pull complete
e887524d2ef9: Pull complete
ccb65627e1c3: Pull complete

UPD Below is output from docker image inspect mysql:5.7 but there is nothing about 69692152171a

[
    {
        "Id": "sha256:2c9028880e5814e8923c278d7e2059f9066d56608a21cd3f83a01e3337bacd68",
        "RepoTags": [
            "mysql:5.7"
        ],
        "RepoDigests": [
            "mysql@sha256:a682e3c78fc5bd941e9db080b4796c75f69a28a8cad65677c23f7a9f18ba21fa"
        ],
        "Parent": "",
        "Comment": "",
        "Created": "2021-05-12T08:11:03.343403499Z",
        "Container": "db38503d38cc5342a2e11abace95c67ea3cc8bb65b48d45bfcda4bcb30748245",
        "ContainerConfig": {
            "Hostname": "db38503d38cc",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "3306/tcp": {},
                "33060/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "GOSU_VERSION=1.12",
                "MYSQL_MAJOR=5.7",
                "MYSQL_VERSION=5.7.34-1debian10"
            ],
            "Cmd": [
                "/bin/sh",
                "-c",
                "#(nop) ",
                "CMD [\"mysqld\"]"
            ],
            "Image": "sha256:4b62934a5405f45c27bf212c6289792743498ce4ff0a5e0f1cdf6b6371320fbf",
            "Volumes": {
                "/var/lib/mysql": {}
            },
            "WorkingDir": "",
            "Entrypoint": [
                "docker-entrypoint.sh"
            ],
            "OnBuild": null,
            "Labels": {}
        },
        "DockerVersion": "19.03.12",
        "Author": "",
        "Config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "3306/tcp": {},
                "33060/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "GOSU_VERSION=1.12",
                "MYSQL_MAJOR=5.7",
                "MYSQL_VERSION=5.7.34-1debian10"
            ],
            "Cmd": [
                "mysqld"
            ],
            "Image": "sha256:4b62934a5405f45c27bf212c6289792743498ce4ff0a5e0f1cdf6b6371320fbf",
            "Volumes": {
                "/var/lib/mysql": {}
            },
            "WorkingDir": "",
            "Entrypoint": [
                "docker-entrypoint.sh"
            ],
            "OnBuild": null,
            "Labels": null
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 446995706,
        "VirtualSize": 446995706,
        "GraphDriver": {
            "Data": {
                "LowerDir": "/var/lib/docker/overlay2/4b355447174887cc24e9c4ce3d03bf66a43f9f12933a51d67447e6e7d3440f68/diff:/var/lib/docker/overlay2/4a933d2f6392c6e7a6bde1a2ec07796647afb48bfd3786a0487814787bcc2e6b/diff:/var/lib/docker/overlay2/dc24d83df2f1b4125d5541e576a18e4f1fabf4aa51ffb55e1670055a3a7765aa/diff:/var/lib/docker/overlay2/28c38b6e267cc02a806eb033998d90d5483e875283993bf15ebd6fb676445aa4/diff:/var/lib/docker/overlay2/8b98e54ac5867901dfb899acd5c8c945f5ea98f69bc99ed4283cbbe5fd1a5b5e/diff:/var/lib/docker/overlay2/c974a8bac2ab3fb407d73d379d1fd8e3ad2d5d37bd84d259aaf5d19dd8e4bb20/diff:/var/lib/docker/overlay2/cf85ba34d9447973763b63e81351759ad4665a182bd42a12f2bf01416cb6236e/diff:/var/lib/docker/overlay2/9dfb686f6a4c9bb5aac551ff50f6c89493e5d37229e8d0a90f1725a4a97b98eb/diff:/var/lib/docker/overlay2/ccbe6e85c920f45001435c90f2bd95d432e2908804631901c6eb00b0290e3a25/diff:/var/lib/docker/overlay2/39c609a115068695fe652ebe45e382b7a9b8651eaf9b9d0a1db631f4ca4352f9/diff",
                "MergedDir": "/var/lib/docker/overlay2/8acf9c4dcbc0241cdb938b766c1035c69716b44617ef8105ae5845ad70189ef8/merged",
                "UpperDir": "/var/lib/docker/overlay2/8acf9c4dcbc0241cdb938b766c1035c69716b44617ef8105ae5845ad70189ef8/diff",
                "WorkDir": "/var/lib/docker/overlay2/8acf9c4dcbc0241cdb938b766c1035c69716b44617ef8105ae5845ad70189ef8/work"
            },
            "Name": "overlay2"
        },
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:02c055ef67f5904019f43a41ea5f099996d8e7633749b6e606c400526b2c4b33",
                "sha256:14be0d40572c9e789898075dab874a65268de67962d8fd775172b206a9305022",
                "sha256:e82f328cb5e68d3c0fcc6604b3c09a2898d94fde76f589abc5163c85e168a075",
                "sha256:b2abc2ad4a418fb408384c726f800fa1f722cbb38987200cd362bc73f20cc988",
                "sha256:570df12e998cd93e68915a6de7002f9ca1e4b21bbaca3cd1124b7770c800b1b4",
                "sha256:ae477702a51387de5407cbaad4e225c3b3ddfb329cb1b00739b4161fe34d80a6",
                "sha256:3182d4b853f01f95a1cc30cd97c3e5e4d1aa3011ba4cf6273c2d5b38ef1adba0",
                "sha256:940ffd6ceda5ac47aeabf50a3210969f1adce1a78b1dd66dab62c20a2c58caa5",
                "sha256:d329e0888b830d8de863fedf17cb8e600f46ff869b82a43d92499fceb7797bf8",
                "sha256:516d3b88eaf6e98711593913e66d73b14c4438aeec0ca57e6378823e7423ec6d",
                "sha256:8dd710df810d11d75e69cfd8dd0db15ebdd13a667069db0638b9d3168218b3f4"
            ]
        },
        "Metadata": {
            "LastTagTime": "0001-01-01T00:00:00Z"
        }
    }
]

Answer 1

The id 69692152171a is the first layer of the image and because you probably have another version of mysql locally that has the same layer as this one, when you did pull the image, this message 69692152171a: Already exists means that there where no changes on that layer between versions.

To see the layers of an image run docker image inspect mysql:5.7

You can read more here: https://docs.docker.com/engine/reference/commandline/pull/#examples