我想出来了！这是语法：
当数据库中有多个john smiths时，用户为jo smith键入“jo”。你需要传入两个变量。
答。他们打字的前两个字母。
b。他们键入的全部字符串。

exports.handler = function(event, context, callback) 
{
    completeCount = 0;
    completeCeiling = 1;

    var returnArray = {
    }

    findPlayer();

    function findPlayer() 
    {
        var params = 
        {
            TableName : "Z_DEV_findPlayerTable",
            KeyConditions: 
            {
                "firstLetters": {
                    ComparisonOperator: 'EQ',
                    AttributeValueList: [
                        event.first2Letters ]
                },
                "firstOrLastName": 
                {
                    ComparisonOperator: 'BEGINS_WITH',
                    AttributeValueList: [
                        event.currentTypedLetters ]
                }
            },
        };

        dynamodb.query(params, function(err, data) 
        { if (err) {
            console.log("break 1A")
                console.log(err, "findPLayer error");
                callback(err);
            } else {
                console.log("break 1B");
                console.log("my data is", data.Items);
                var folderKeys = Object.keys(data.Items);
                completeCeiling = folderKeys.length;
                for(i = 0; i < folderKeys.length; i++)
                {
                    var filteredPlayer = JSON.stringify(data.Items[folderKeys[i]].firstOrLastName);
                    var splitString = filteredPlayer.split('+');
                    var filteredID = splitString[1];
                    filteredID = filteredID.replace(/['"]+/g, '')

                    console.log("my filteredPlayer is ", filteredPlayer);
                    console.log("my filteredID2 is ", filteredID);
                    getPlayer(filteredID);
                }

            }
        });
    }

     function getPlayer(playerID) {

        var params = {
            TableName : "Z_DEV_playerTable",
            Key: {
                "playerID": playerID
            },
        };
        dynamodb.get(params, function(err, data)
            { if (err) {
                console.log(err);
                console.log("break 2A");
            } else 
            {
                console.log("break 2B");
                //console.log("my data.Item is ",data.Item)
                if(data.Item != undefined)
                {
                    returnArray[playerID] = data.Item
                    completeCount++;
                    console.log("completeCount is " + completeCount);
                    if (completeCount === completeCeiling) 
                    {
                        callback(null, JSON.stringify(returnArray)); 
                    }
                }
                else
                {
                    console.log("player doesn't exist");
                }
            }
        });   
    }
};