PHP / SQL：如何从一个表中选择完全不同的表中不存在的值

Question

I have two tables, one with a list of projects and who is assigned to each project, and one with names and information about contractors.

"Projects_table"
Project_ID    Contractor_assigned    Job_Complete
1             Jim Smith              1
2             John Smith             0
3             Edward Smith           0
4             Smith Smith            1
5             Candle Stick           1

and

"Contractors_Table"
Contractor_ID    Name              Drywall     Insulation
1                Jim Smith         1           0
2                John Smith        0           1
3                Edward Smith      0           1
4                Smith Smith       0           1
5                Jack BeNimble     0           1
6                Jack BeQuick      1           0
7                Candle Stick      0           1

What I need, is to pull an SQL query that gives me a list of the Contractors of a certain type (Drywall or Insulator) who are currently not assigned to any job, so long as that job is also not marked "Complete."

I've tried a few versions of this, but with no success:

SELECT
Name FROM Contractors_Table
WHERE Contractors_Table.Insulation=1
AND Name NOT IN
(SELECT Contractor_assigned FROM Projects_table WHERE `Job_Complete` = 0)

What I'm hoping for output from my above example is to get back:

Jack BeNimble
Candle Stick

Those two Insulators are not currently assigned a job, excluding the "complete" job.

Answer 1

You should use NOT EXISTS instead:

SELECT Name
  FROM Contractors_Table c
 WHERE c.Insulation = 1
   AND NOT EXISTS
       (SELECT 1 
          FROM Projects_table p
         WHERE p.Job_Complete = 0
           AND p.Contractor_assigned = c.Name)

You could refactor the query you are trying to do, but will take much more effort to use NOT IN .

You should also use foreign keys instead of names to compare data. You are duplicating information in relational database, which doesn't follow Normalization rules

Answer 2

Firstly your table design is wrong: you should store the Contractor_ID in the project table, and not their names (what happens with homonyms???)

Secondly I don't understand why your query doesnt return the expected result because it looks correct. Maybe because you have a column named Name , and this is a reserved keyword, and you should thus surround it with `

Anyway it's never efficient to do a NOT IN

You can rewrite that with an OUTER JOIN :

SELECT C.`Name` 
FROM Contractors_Table C
LEFT JOIN Projects_table P ON C.`Name` = P.`Contractor_assigned` AND P.`Job_Complete` = 0
WHERE C.Insulation=1
  AND P.ID IS NULL --> This will ensure that you only get those who are not in the Project table

Answer 3

Obviously a couple of queries (one for each type). If you use unique ID's in both tables for each of the contractors you can join the tables and select where Contractors_Table.drywall = 0 and Project_Table = 0 (Group by Contractor ID).

I think its just about getting your data sorted in your tables then writing the query.

HTH :-)