Java中将输入数据与Sql表进行比较的有效方法

Question

First of all I will explain my use case:

I will get a String Array of names from user(Can of size 2,5,1)

e.g Suppose user input is like this: 
String[] names={"Micheal", "Joe","Jim"}

Now after taking input from user, I have to hit SQL table called "USERS" and check whether all of these names are present in USERS table or not. If any single name is not present then return false. If all names are present in USERS table then return true.

My Idea:

My idea is to hit USERS table. Get all names of USERS table in a String array (named as all_names) and then compare my input string(ie names) with this all_names String. So if names is subset of all_names then return true else return false.

Problem:

But I think this is not an efficient solution. When this table will expand then I will have thousands of records so this technique will be very exhaustive. Any other better and efficient solution for this please.

Updated Solution:

Suppose names in USERS table are unique.

Thanks for your replies. Now I have adopted this approach after getting help from your answers. I want to know that this solution is a better approach or not:

            String[] names={"Micheal","Jim","Joe"};


            String list2string =  StringUtils.join(names, ", "); 
            //connection was established previosuly
            stmt = conn.createStatement();
            System.out.println(list2string);
            rs = stmt.executeQuery("SELECT COUNT(*) AS rowcount FROM USERS WHERE name IN (" + 
            list2string + 
            ")");

            rs.next();
            int count = rs.getInt("rowcount");
            rs.close();
            if(names.length==count){
                System.out.println("All names are in users table");
            }else{
                System.out.println("All names are not present in users table");
            }

Want your comments on this updated solution please.

Regards

Answer 1

You are right, this is not really efficient.

It is the database job to do such things.

You can either make a select statement for each name, eg.

SELECT name FROM users WHERE name = 'Micheal'

or

SELECT name FROM users WHERE name IN ('Micheal', 'Joe', 'Jim')

and check the returned rows.

It might be quiet different depending on which framework you use to query the database.

Answer 2

you can form a string out of string array using loop
for example if you have string array like this:
String[] names={"Micheal", "Joe","Jim"} get a string lets say s -> "Micheal", "Joe","Jim"
now query like this:
String sql = SELECT name FROM users WHERE name IN (" + s + ")". (you can check the format).
get the output collection and compare with the given collection.

Answer 3

One way to do it, could be

SELECT
    COUNT(DISTINCT name)
FROM
    users
WHERE
    name IN ('Micheal', 'Joe', 'Jim')

Then check if the count is equal to your parameter count, in our case, we should get 3.

Answer 4

I will get a String Array of names from user(Can of size 2,5,1)

You get the input from user, you hit the database with query:

SELECT (WHATEVER_YOU_NEED) FROM SCHEMA_NAME.TABLE_NAME WHERE COLUMN IN (USER_PROVIDED_INPUT);

You store this result in List.

Get all names of USERS table in a String array (named as all_names) and then compare my input string(ie names) with this all_names String. So if names is subset of all_names then return true else return false.

Yes, you are right, so you will use

Use Collection.containsAll() :

boolean isSubset = listA.containsAll(listB);

And, if your database has unique names (which I guess can be duplicate), you can simply get the count from SQL Query and match it with the user input.

I hope this will help.

Answer 5

SELECT IF(
    ( SELECT COUNT(DISTINCT name) FROM users WHERE name IN ({toSearch}) ) = {Count},
    , 1 , 0
) as Result

replace {toSearch} with eg 'Micheal', 'Joe', 'Jim' {count} is the number of searche, in this example 3. so if all exist the column "Result" has the value 1 else 0