MYSQL NOT IN子选择

Question

I have two table

1. item
2. confirmmasterdetail

I want to select records from item table whose is not in confirmmasterdetail table when me run this query at that it's return empty result set.

SELECT itemId
,      itemName
FROM   item
LEFT 
JOIN   item /* HERE AN ALIAS IS MISSING, ITEM occurs twice. */
ON     item.itemId = confirmmasterdetail.itemId
WHERE  confirmmasterdetail.itemId 
       NOT IN 
       ( SELECT confirmmasterdetail.itemId
         FROM   confirmmasterdetail
       )
AND    confirmMasterId = ".$_REQUEST['confirmMasterId'];

Answer 1

See your query. Please prefix all columns selected with either table name or (better) add an alias to each table and use that one. Also note that item occurs twice in the query, so column names might not be what they seem to be.

Finally, ensure null can not be returned from the subselect.

Answer 2

I believe your query has basic conceptual problems with SQL. It is hard to give advice without a clear statement of what you want and how the tables look like. To help you, we need at least information about the tables (what columns and how are they connected).

Edit : With the information you provided you might want to try one of these queries:

1. Select all items that have no corresponding entry in confirmmasterdetail:

    SELECT itemId , itemName FROM item WHERE item.itemId NOT IN ( SELECT confirmmasterdetail.itemId FROM confirmmasterdetail ); 

2. Select all items that have no entry in confirmmasterdetail with the given confirmMasterId:

    SELECT itemId , itemName FROM item WHERE item.itemId NOT IN ( SELECT confirmmasterdetail.itemId FROM confirmmasterdetail WHERE confirmMasterId = ".$_REQUEST['confirmMasterId'] ); 

Answer 3

There is one important thing about null in SQL, it means unknown not nothing . So if your sub-query returns null values, it means unknown , and not in unknown makes DBMS to ignore all records.

Just change the subquery to:

SELECT confirmmasterdetail.itemId
  FROM confirmmasterdetail
 WHERE confirmmasterdetail.itemId is not null

Answer 4

Try this query -

SELECT
  i.*
FROM item i
  LEFT JOIN confirmmasterdetail c
    ON i.itemId = c.itemId
WHERE
  c.itemId IS NULL