使用第一个表的输出从第二个表中选择特定数据

Question

I have two table. One is account and the other is client table. The user will give input and in this case is 19 . What I want to do is that I want to select ONLY a single name from client using client_id as identifier and only using a single select statement. I could do select query twice but that's not what I wanted.

So to explain it better: User give input such as $id = 19 , I will use id from account table to identify client_id which in this case is 17 . I will then select name from client table using client_id .

account table

client table

I already take a look at join and left join and I'm still stuck. Please help me with this. Thanks in advance.

My current not working code:

$sql = " SELECT account.id, client.client_id\n"
    . " FROM account, client\n"
    . " WHERE account.id = 19";

Answer 1

A simple inner join will do the task

 $query = "select 
                  account.id,client.client_id 
           from 
                  account 
           join 
                  client 
            on 
                  account.client_id = client.client_id 
           where 
                  account.id = 19";

Answer 2

This should work using an INNER JOIN :

SELECT c.name
FROM Client C
   INNER JOIN Account A ON C.Client_Id = A.Client_Id
WHERE A.Id = 19

You're query is producing a Cartesian Product since you aren't joining the tables on any field.

• A Visual Explanation of SQL Joins

Answer 3

You didn't join Account and Client. And moreover you want only the client name and the query has to be:

Select distinct client.client_name from account, client where client.client_id=account.account_id and account_id=19 

Answer 4

You need to specify which column is used to join the two tables.

It's an unfortunate fact about the SQL language that the default behavior is to join two tables by matching each row in one table to every row in the other table. That is, every possible pairing is part of the result set. SQL doesn't have any way of inferring which column(s) you want to use as the join criteria, so you have to specify the condition yourself.

Here's a better form for the query:

$sql = " SELECT account.id, client.client_id
    FROM account JOIN client USING (client_id) 
    WHERE account.id = 19";

Do use the JOIN syntax. It has been the standard way of doing joins in SQL since 1992. The comma-style syntax is only for backward compatibility with pre-1992 SQL. They perform exactly the same, but the 1992 syntax can do outer joins and it's easier to read.

PS: PHP supports multi-line strings, so there's no need to concatenate strings together as you're doing. That's a Java habit.

Answer 5

$sql = " SELECT account.id, client.client_id
           FROM `account`
     INNER JOIN `client` ON `client`.client_id = `account`.`client_id`
          WHERE account.id = 19";

Answer 6

Since you didn't provide information about the structure of your client table, this is just a guess:

SELECT account.id, client.client_id
FROM account, client
WHERE account.id = 19
  AND account.client_id = client.id

Answer 7

Maybe you should try:

$sql = "SELECT account.id, client.client_id
        FROM account, client
        WHERE account.client_id=client.id AND account.id = 19 "

Answer 8

这应该为您完成。从帐户c.name，c.client_id，a.id到客户端c的左连接上a.client_id = c.client_id，其中a.id = 19