An example of using ethereum to save data.

EthAsDB.sol

// Estimated Gas: 1,368,083
pragma solidity ^0.4.24;

library StringOperation {function concat(string string1, string string2, string sep) internal pure returns (string){

        bytes memory string1Bytes = bytes(string1);
        bytes memory string2Bytes = bytes(string2);
        bytes memory sepBytes = bytes(sep);

        string memory concatString = new string(string1Bytes.length + sepBytes.length + string2Bytes.length);
        bytes memory concatStringBytes = bytes(concatString);
        uint k = 0;

        // Concat string1
        for (uint i = 0; i < string1Bytes.length; i++) concatStringBytes[k++] = string1Bytes[i];
        // Concat sep
        for (i = 0; i < sepBytes.length; i++) concatStringBytes[k++] = sepBytes[i];
        // Concat string2
        for (i = 0; i < string2Bytes.length; i++) concatStringBytes[k++] = string2Bytes[i];

        return string(concatStringBytes);
    }
}

contract DBExample {
    using StringOperation for *;

    struct SomeStruct {
        string data1;
        string data2;
        string data3;
        string data4;
    }

    address owner;
    address[] private admins;
    // user => SomeStruct
    mapping (address => SomeStruct[]) userSomeStruct;

    event BroadcastSomeStruct(address receiver, string data3, string dataDetails);

    // modifier to check if caller is owner
    modifier ifOwner() {
        if (msg.sender != owner) {
            revert();
        }
        _; /*  _means contiune normal flow */
    }

    constructor() public {
        owner = msg.sender;
        admins.push(owner);
    }

    function assignSomeStruct(address user, string data1, string data2, string data3, string data4) public ifOwner {

        SomeStruct memory someStruct;
        someStruct.data1 = data1;
        someStruct.data2 = data2;
        someStruct.data3 = data3;
        someStruct.detail = data4;

        userSomeStruct[user].push(someStruct);

        emit BroadcastSomeStruct(user, data3, data4);
    }

    function viewAllSomeStruct(address user) public constant returns (string allSomeStruct){

        SomeStruct[] memory someStructs = userSomeStruct[user];
        string memory someStructString;

        for(uint i = 0; i < someStructs.length; i++) {
            someStructString = StringOperation.concat(
                                    someStructs[i].data1,
                                    someStructs[i].data2,
                                    "   ");
            someStructString = StringOperation.concat(
                                    someStructString,
                                    someStructs[i].data3,
                                    "   ");
            someStructString = StringOperation.concat(
                                    someStructString,
                                    someStructs[i].detail,
                                    "   ");
            if (i > 0) {
                allSomeStruct = StringOperation.concat(
                                    allSomeStruct,
                                    someStructString,
                                    ",");
            } else {
                allSomeStruct = someStructString;
            }
        }
        allSomeStruct = StringOperation.concat(
                            "SomeStructID  data2  data3   SomeStructDetail",
                            allSomeStruct,
                            ",");
    }

    function viewSomeStructByData2(address user, string data2) public constant returns (string someStruct){

        SomeStruct[] memory someStructs = userSomeStruct[user];

        for(uint i = 0; i < someStructs.length; i++) {
            if (keccak256(someStructs[i].data2) == keccak256(data2)) {
                someStruct = StringOperation.concat(
                                someStructs[i].data1,
                                someStructs[i].data2,
                                "   ");
                someStruct = StringOperation.concat(
                                someStruct,
                                someStructs[i].data3,
                                "   ");
                someStruct = StringOperation.concat(
                                someStruct,
                                someStructs[i].detail,
                                "   ");
                someStruct = StringOperation.concat(
                                "SomeStructID  data2  data3   SomeStructDetail",
                                someStruct,
                                ",");
            }
        }
    }
}