title: SQL Server Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >=
body: <p>I run the following query:</p>
  
  <pre><code>SELECT 
     orderdetails.sku,
     orderdetails.mf_item_number,
     orderdetails.qty,
     orderdetails.price,
     supplier.supplierid,
     supplier.suppliername,
     supplier.dropshipfees,
     cost = (SELECT supplier_item.price
             FROM   supplier_item,
                    orderdetails,
                    supplier
             WHERE  supplier_item.sku = orderdetails.sku
                    AND supplier_item.supplierid = supplier.supplierid)
  FROM   orderdetails,
         supplier,
         group_master
  WHERE  invoiceid = '339740'
         AND orderdetails.mfr_id = supplier.supplierid
         AND group_master.sku = orderdetails.sku  
  </code></pre>
  
  <p>I get the following error:</p>
  
  <blockquote>
    <p>Msg 512, Level 16, State 1, Line 2
    Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, &lt;, &lt;= , >, >= or when the subquery is used as an expression.</p>
  </blockquote>
  
  <p>Any ideas?</p>