how to join two tables with a where condition and display the records

Question

So I had a hard time finding a good answer on Stack. I'm looking to run a query that combines the information on two tables together. So far this is what i have got. The actual scenario is as follows:

I will try to explain a bit more from my side to achieve this:

I have two tables :

Comparitive_st_sup
___________________

id  | tender_id | item_name | slno | supplier_name | prod_description
________________________________________________________________________

1       401        Collinear   1      OnlineMetals    Description comes here    
2       401        Filter      2      OnlineMetals    Description comes here
3       401        Antenna     3      OnlineMetals    Description Comes here
4       455        Primer      1      KR Electronics  Description comes here
5       455        Chock       2      KR Electronics  Description comes here


comparitive_st_tech_compliance
_______________________________

id | tender_id | item_name  | slno | supplier_name  | tech_analyst_comment
__________________________________________________________________________

1      401        Collinear    1      OnlineMetals     90%
2      401        Filter       2      OnlineMetals     25%
3      401        Antenna      3      OnlineMetals     87%
4      455        Primer       1      KR Electronics   64%
5      455        Chick        2      KR Electronics   80%

Now i am expecting a result like:

401    Collinear     1    OnlineMetals    Description comes here   90%
401    Filter        2    OnlineMetals    Description comes here   25%
401    Antenna       3    OnlineMetals    Description comes here   87%

As per the tender_id selected the value is passing as a querystring and the records has to be displayed accordingly. Help appreciated..

I tried this, but result is not proper:

 Select comparitive_st_sup.*,
  comparitive_st_sup.tender_id As tender_id1,
  comparitive_st_sup.supplier_name As supplier_name1,
  comparitive_st_sup.slno As slno1,
  comparitive_st_sup.prod_description As prod_description1,
  comparitive_st_sup.item_name As item_name1,
  comparitive_st_sup.total As total1,
  comparitive_st_tech_compliance.tech_analyst_comment
  From comparitive_st_tech_compliance
  Right Join comparitive_st_sup On comparitive_st_sup.tender_id =
  comparitive_st_tech_compliance.tender_id
  Where comparitive_st_sup.tender_id = 401     

I need to display all the fields from comparitive_st_sup and only one field (tech_analyst_comment) with a where condition tender_id. Now the records are duplicating. Instead of 3 records to show, it is showing 9 records. Am i making any mistake?

Answer 1

from your comment, I believe comparitive_st_tech_compliance has more then one row against a row in comparitive_st_sup table for a single tender_id. if it is so then it will return multiple row doesn't matter which Join you use.

Answer 2

You may need to do so here:

Select comparitive_st_sup.*,
  comparitive_st_sup.tender_id As tender_id1,
  comparitive_st_sup.supplier_name As supplier_name1,
  comparitive_st_sup.slno As slno1,
  comparitive_st_sup.prod_description As prod_description1,
  comparitive_st_sup.item_name As item_name1,
  comparitive_st_sup.total As total1,
  comparitive_st_tech_compliance.tech_analyst_comment
  From comparitive_st_tech_compliance
  Where comparitive_st_sup.tender_id = 401  AND comparitive_st_tech_compliance.tender_id =  tender_id1

Answer 3

SELECT comparitive_st_sup.*,
  comparitive_st_sup.tender_id As tender_id1,
  comparitive_st_sup.supplier_name As supplier_name1,
  comparitive_st_sup.slno As slno1,
  comparitive_st_sup.prod_description As prod_description1,
  comparitive_st_sup.item_name As item_name1,
  comparitive_st_sup.total As total1,
  comparitive_st_tech_compliance.tech_analyst_comment
  FROM comparitive_st_sup, comparitive_st_tech_compliance
  WHERE comparitive_st_sup.tender_id = 401
  AND comparitive_st_tech_compliance.tender_id = comparitive_st_sup.tender_id
  GROUP BY comparitive_st_sup.tender_id;

Answer 4

If you don't want or can't GROUP BY , you could try a sub-query. You can also ORDER BY date/id in the sub-query.

SELECT
    cs.*,
    cs.tender_id AS tender_id1,
    cs.supplier_name AS supplier_name1,
    cs.slno AS slno1,
    cs.prod_description AS prod_description1,
    cs.item_name AS item_name1,
    cs.total AS total1,
    (
        SELECT
            ct.tech_analyst_comment
        FROM comparitive_st_tech_compliance AS ct
        WHERE ct.tender_id = cs.tender_id
        LIMIT 1
    ) AS tech_analyst_comment
FROM comparitive_st_sup AS cs
WHERE cs.tender_id = 401

---

LE: IF and ONLY IF slno is the same identifier in both of your tables ( comparitive_st_sup.slno = comparitive_st_tech_compliance.slno ), than you can join them with the extra join argument of AND comparitive_st_sup.slno = comparitive_st_tech_compliance.slno so your initial query will look something like this:

Select comparitive_st_sup.*,
  comparitive_st_sup.tender_id As tender_id1,
  comparitive_st_sup.supplier_name As supplier_name1,
  comparitive_st_sup.slno As slno1,
  comparitive_st_sup.prod_description As prod_description1,
  comparitive_st_sup.item_name As item_name1,
  comparitive_st_sup.total As total1,
  comparitive_st_tech_compliance.tech_analyst_comment
From comparitive_st_tech_compliance
Right Join comparitive_st_sup On
    comparitive_st_sup.tender_id = comparitive_st_tech_compliance.tender_id AND
    comparitive_st_sup.slno = comparitive_st_tech_compliance.slno
Where comparitive_st_sup.tender_id = 401

but if slno differs in table *_st_sup and *_tech_compliance than you will need to add a relationship between the products and comments beside the tender_id

comparitive_st_tech_compliance
+-----------------------------------------------------------------------------------------+
| id | tender_id | product_id | item_name  | slno | supplier_name  | tech_analyst_comment |
+-----------------------------------------------------------------------------------------+
|  1 | 401       |     1      | Collinear  |   1  | OnlineMetals   | description          |
+-----------------------------------------------------------------------------------------+

where comparitive_st_tech_compliance.product_id is Comparitive_st_sup.id, which also brings me to the point where I would suggest you to change your database schema ( structure )

Side note: So from your database structure, one thing to point out is that it's poorly designed. You have duplicate fields in both tabels, so if you need to update for ex. supplier_name you will need to update all of your tables. Now assuming you are willing to make the changes, I would suggest to split up your data into 3 tables, not taking into account that slno may be an identifier between the 2 tables.

comparative_supplier
+---------------------+
| id | supplier_name  |
+---------------------+
| 1  | OnlineMetals   |
| 2  | KR Electronics |
+---------------------+

comparitive_st_sup
+--------------------------------------------------------------------+
| id | tender_id | supplier_id | slno | item_name | prod_description |
+--------------------------------------------------------------------+
| 1  | 401       |      1      |   1  | Collinear | description      |
| 2  | 401       |      1      |   2  | Filter    | description      |
| 3  | 401       |      1      |   3  | Antenna   | description      |
| 4  | 455       |      2      |   1  | Primer    | description      |
| 5  | 455       |      2      |   2  | Chock     | description      |
+--------------------------------------------------------------------+

comparitive_st_tech_compliance
+-----------------------------------------+
| id   | id_supply | tech_analyst_comment |
+-----------------------------------------+
| 15   |     1     |         90%          |
| 56   |     2     |         25%          |
| 123  |     3     |         87%          |
| 412  |     4     |         64%          |
| 684  |     5     |         80%          |
+-----------------------------------------+

with this table structure you can easily join your tables without duplicate entries and change fields without the need to update all your tables.

SELECT
    cs.tender_id, sn.supplier_name, cs.slno, cs.item_name,
    cs.prod_description, ct.tech_analyst_comment
FROM comparitive_st_sup AS cs
LEFT JOIN comparative_supplier AS sn ON sn.id = cs.supplier_id
LEFT JOIN comparitive_st_tech_compliance AS ct ON ct.id_supply = cs.id
WHERE cs.tender_id = 401

or just change your st_sup table and include the the tech comment, because the 2 tables only differ by the tech comment and product description