根据表数据有条件地执行SQ​​L查询/语句

Question

First, take a look at this table, basically I need to UPDATE (+1) a ticket WHERE the Username equals to Jondoe AND Money is greater than 200.

Now, I know I can execute 3 queries, first to check if the actual user has Jondoe as Username, then check if he has enough Money and if these results are true, then UPDATE (+1) a ticket finally.

I'm learning SQL and i'm working over a mssql database, what's the proper way to do such a conditional query/update? Can I avoid using that many queries?

I'm also working with laravel framework, I don't know if it comes with any "tool" to accomplish what I want.

Thanks in advance

Answer 1

What you are looking for is to use the UPDATE statement and the WHERE statement to seive out what you require, and this is how you do it. Parse the command through laravel and it will update accordingly.

UPDATE TableName Set Tickets=Tickets+1 WHERE USERNAME='JonDoe' AND Money > 200

Answer 2

使用Eloquent：

\App\User::where('username','JonDoe')->where('Money','>',200)->increment('Tickets');

Answer 3

I'm not expert with Laravel, but as many other frameworks, it should have an ORM system ( Object Relational Mapping : https://en.wikipedia.org/wiki/Object-relational_mapping ), this systems helps you to 'speak' to databases in an object oriented fashion ( with methods like getFirstByPrimaryKey( $primaryKey ) ).

This said, I think that kind of systems are better when you already know how to do it manually.

In the case you are proposing, you have to think first what you need, and then think what's the better approach to accomplish it.

What you need:

Insert a ticket for one user if that user has more or equals some quantity.

Let me suppose, perhaps you're going to detry that quantity from money field after a successful ticket creation, right ?

So I think we're selling a ticket, and the normal steps should be:

• Check if user is logged. If it's logged, we probably have the user id in session or a similar system. It's much better to search in indexed numeric fields, if possible.

• Once we have the user_id, we update the row if that user id has enough money for this action:

//pseudo code
        $userId = 12;
        $cost = 200;
        $query = "update ticketstable set tickets=tickets+1, money=money-$cost 
    where id='$userId' and money >= $cost";
        $result = $db->query($query);

        if($result){
          //row with id = $userId has been updated
        }else{
          //There's not a row with $userId, or that row's money was less than $cost
        }

Take in account when dealing with money operations that you should make all related queries as a transaction ( a transaction in database argot means several sql sentences executed together, in a way that if some fails, all others are reverted, to avoid inconsistency ).

If you divide my proposal in two queries:

1) check if user with id=x has money >= $cost;

2) update money -= $cost;

You can find in a situation where the user or other automated process takes some money from the same row between the steps 1 and 2, and then you end with negative money, and allowing an operation you shouldn't.

Answer 4

Laravel has the fluent query builder which you can use (more or less) like below:

$affectedRows = DB::table('TableName')
    ->where("Username", "Jondoe")
    ->where("Money",">",200)
    ->increment("Tickets");

You can also use $affectedRows to check if there were any updates made.

Edit:

If you have a user model (eg named User ) then you can use the same syntax but with Eloquent.

Example:

User::where("Username", "Jondoe")
    ->where("Money",">",200)
    ->increment("Tickets");

Eloquent is Laravel's ORM (Object-Relational model) which provides a mapping between relational databases and PHP objects (ie the model part of the MVC framework). It's not a query builder itself but it does use fluent in the background to build queries.

Reference https://laravel.com/docs/5.0/queries

Answer 5

Try This Command

UPDATE TableName Set Tickets=Tickets+1 WHERE USERNAME='JonDoe' AND Money > 200

Hopefully This will solve your problem