从一个表中选择带有AND子句的数据，然后从另一个表中选择一个列？

Question

I am trying to select two columns from one table with an AND clause while also just selecting a column from another table.

The process I want to achieve is that the query reads one table for a username and password using the AND clause to validate whether the entered credentials are correct and another part of the process which just reads another table for one column (the column in this table is associated with the same username as the above table)

SQL in C# for selecting data in one table

SELECT TwyID, PW 
FROM LoginTbl 
WHERE TwyID = '"+TwyID_txt.Text+"' 
  AND PW = '"+Pw_txt.Text+"'"

For selecting data in the other table

SELECT Class 
FROM UserInfo 
WHERE TwyID = '"+TwyID_txt.Text+"'

I simply just like to merge these two SQL statements into one.

I've looked at the user of JOINS but they don't seem to work how ever I try to implement them.

I tried one solution being:

SELECT 
    TwyID, PW, 
    (SELECT Class 
     FROM UserInfo 
     WHERE TwyID = '"+TwyIDTextBox.Text+"') 
FROM LoginTbl 
WHERE TwyID = '" + TwyIDTextBox.Text + "' 
  AND PW = '" + PasswordTextBox.Text + "'";

Although this was to no avail.

I'm sure I am being dim and the solution is rather simple, but trying new things never goes without its problems right? :-)

Hope anyone can help.

Thanks, Liam

Answer 1

You should use INNER JOIN here:

SELECT L.TwyID, L.PW
WHERE L.TwyID = '" + TwyIDTextBox.Text + "' 
    AND L.PW = '" + PasswordTextBox.Text + "'"
FROM LoginTbl L INNER JOIN UserInfo U ON L.TwyID = U.TywID

On a side note, you should never ever create SQL directly from user input. There is a huge security risk (SQL Injection) in doing that.

Answer 2

Why don't try Join statement?

Select T1.TwyID,T1.PW,T2.Class
From LoginTbl as T1
Join UserInfo as T2 on T1.TwyID = T2.TwyID
Where T1.TwyID = '"+TwyID_txt.Text+"' AND T1.PW = '"+Pw_txt.Text+"'"

Answer 3

if you don't want to use join you can try this

    select t.Id,t.Password,class
    from
    (select TwyID as 'Id', PW as 'Password' from LoginTable
    where TwyID = '"+TwyIDTextBox.Text+"' and PW = '" + PasswordTextBox.Text + "')as t,UserInfo u
    where u.Id= '"+TwyIDTextBox.Text+"'

but inner join is better.

Answer 4

Turns out a LEFT JOIN was what I needed.

SELECT *
FROM LoginTbl
LEFT JOIN UserInfo
ON LoginTbl.TwyID = UserInfo.TwyID
WHERE LoginTbl.TwyID = '"+TwyIDTextBox.Text"'
AND LoginTbl.PW = '"+PasswordTextBox.Text+"'

This solution selects all fields in the UserInfo table where the TwyID matched the TwyID from the LoginTbl. From this I was able to read the Class field from the UserInfo table into a variable and it worked!

Thank you everyone for all your answers, opened mind to play with the statement eventually getting it to work.