The following query will not return any data. Cannot figure out why. Removing one of the joins works but then I can't get data from one table.
$productInfo = "SELECT stock.*, s_list.*, c_list.*
FROM stock
INNER JOIN s_list
ON stock.s_compo_id = s_list.id
INNER JOIN c_list
ON stock.c_compo_id = c_list.id
WHERE batch_id = '$productID'";
This is your query:
SELECT stock.*, s_list.*, c_list.*
FROM stock INNER JOIN
s_list
ON stock.s_compo_id = s_list.id INNER JOIN
c_list
ON stock.c_compo_id = c_list.id
WHERE batch_id = '$productID'";
Here are some reasons that I readily think of that you would get no data:
batch_id and $productID don't match. The names are different, so why should I think they refer to the same thing?
Either s_list or c_list (or both) have no matching records. You're doing inner joins, so no matching records would mean no rows are returned.
You are getting rows, but the columns have the same names in the two tables. For instance, you will likely see one id column in your output, and it is not clear which table it comes from. Explicitly list the columns you want and give them unique aliases.
And, less likely because the naming looks right:
The join conditions for one or both joins are not correct, so nothing matches.
And, an obligatory note that you should not be putting variables directly into query strings. Use parameters. Not only is it safer, but it gives the engine that opportunity to cache the query plan, saving effort when called multiple times.
Try with the below query.
$productInfo = "SELECT stock.*, s_list.*, c_list.*
FROM stock
LEFT JOIN s_list
ON stock.s_compo_id = s_list.id
LEFT JOIN c_list
ON stock.c_compo_id = c_list.id
WHERE batch_id = '$productID'";
Related
I have a SQL query that works in Access 2016:
SELECT
Count(*) AS total_tests,
Sum(IIf(score>=securing_threshold And score<mastering_threshold,1,0)) AS total_securing,
Sum(IIf(score>=mastering_threshold,1,0)) AS total_mastering,
total_securing/Count(*) AS percent_securing,
total_mastering/Count(*) AS percent_mastering,
(Count(*)-total_securing-total_mastering)/Count(*) AS percent_below,
subjects.subject,
students.year_entered,
IIf(Month(Date())<9,Year(Date())-students.year_entered+6,Year(Date())-students.year_entered+7) AS current_form,
groups.group
FROM
((subjects
INNER JOIN tests ON subjects.ID = tests.subject)
INNER JOIN (students
INNER JOIN test_results ON students.ID = test_results.student) ON tests.ID = test_results.test)
LEFT JOIN
(SELECT * FROM group_membership LEFT JOIN groups ON group_membership.group = groups.ID) As g
ON students.ID = g.student
GROUP BY subjects.subject, students.year_entered, groups.group;
However, I wish to filter out irrelevant groups before joining them to my table. The table groups has a column subject which is a foreign key.
When I try changing ON students.ID = g.student to ON students.ID = g.student And subjects.ID = g.subject I get the error 'JOIN expression not supported'.
Alternatively, when I try adding WHERE subjects.ID = groups.subject to the subquery, it asks me for the parameter value of subjects.ID, although it is a column in the parent query.
Googling reveals many similar errors but they were all resolved by changing the brackets. That didn't help.
Just in case the table relationships help:
Thank you.
EDIT: Sample database at https://www.dropbox.com/s/yh80oooem6gsni7/student%20tracker.ACCDB?dl=0
MS Access queries with many joins are difficult to update by SQL alone as parenetheses pairings are required unlike other RDBMS's and these pairings must follow an order. Moreover, some pairings can even be nested. Hence, for beginners it is advised to build queries with complex and many joins using the query design GUI in the MS Office application and let it build out the SQL.
For a simple filter on the g derived table, you could filter subject on the derived table, g, but likely you want want all subjects:
...
(SELECT * FROM group_membership
LEFT JOIN groups ON group_membership.group = groups.ID
WHERE groups.subject='Earth Science') As g
...
So for all subjects, consider re-building query from scratch in GUI that nearly mirrors your table relationships which actually auto-links joins in the GUI. Then, drop unneeded tables.
Usually you want to begin with the join table or set like groups and group_membership or tests and test_results. In fact, consider saving the g derived table as its own query.
Then add the distinct record primary source tables like students and subjects.
You may even need to play around with order in FROM and JOIN clauses to attain desired results, and maybe even add the same table in query. And be careful with adding join tables like group_membership (two one-to-many links), to GROUP BY queries as it leads to the duplicate record aggregation. So you may need to join aggregates queries by subject.
Unless you can post content of all tables, from our perspective it is difficult to help from here.
Your subquery g uses a LEFT JOIN, but there is a enforced 1:n relation between the two tables, so there will always be a matching group. Use a INNER JOIN instead.
With g.subject you are trying to join on a column that is on the right side of a left join, that cannot really work.
Also you shouldn't use SELECT * on a join of tables with identical column names. Include only the qualified column names that you need.
LEFT JOIN
(SELECT group_membership.student, groups.group, groups.subject
FROM group_membership INNER JOIN groups
ON group_membership.group = groups.ID) As g
ON (students.ID = g.student AND subjects.ID = g.subject)
I would call the columns in group_membership group_ID and student_ID to avoid confusion.
I don't have the database to test, but I would use subject table as subquery:
(SELECT * FROM subject WHERE filter out what you don't need) Subj
Then INNER JOIN this new Subj Table in your query which would exclude irrelevant groups.
Also I would never create join in WHERE clause (WHERE subjects.ID = groups.subject), what this does it creates cartesian product (table with all the possible combinations of subjects.ID and groups.subject) then it filters out records to satisfy your join. When dealing with huge data it might take forever or crash.
Error related to "Join expression may not be supported"; do datatypes match in those fields?
I solved it by (a lot of trial and error and) taking the advice here to make queries in the GUI and joining them. The end result is 4 queries deep! If the database was bigger, performance would be awful... but now its working I can tweak it eventually.
Thank you everybody!
I have 7 Tables as per attached following Image.
I will either enter Engine Number or Chassis Number and it should show the respective tables information (these tables have only mentioned fields) so all fields can be shown as result.
I can use hard coded Engine Number or Chassis Number. Every time of execution of this Query, I will hard code the required Engine/Chassis Number and will get the result.
Can anybody please help me to write this query for me?
Click Here to See the Tables
This might be a starting point for your solution.
SELECT prod.EngineNo AS engNo, prod.ChassisNo, doral.doralNo [, table.column [AS name]]
FROM DOProductSpecsDetais AS prod
INNER JOIN DORAL AS doral
ON prod.DOProductSpecsDetailID = doral.DOProductSpecsID
INNER JOIN DOProductDetail AS prodDetail
ON prod.DOProductDetailID = prodDetail.DOProductDetailID
WHERE prod.ChassisNo = '<input>' OR prod.EngineNo='<input>'
Between the SELECT and the FROM Statement, you can select any column out of your JOIN.
You can cascade as many JOINs as you like...
Which DBMS are you going to use?
One suggestion: Try to simplify the names of your columns, if possible.
One more: If you just started to do Database things, it is always helpful to start a test environment and use a client tool.
You can write query something like this:
select * from
DoProductSpecsDetail tbl1 inner join Doral tbl2
on tbl1.DoProductSpecsDetailId = tbl2.DoProductSpecsId
inner join DoproductDetail tbl3
on tbl1.DoProductDetailId = tbl3.DoProductDetailId
inner join ProductColor tbl4
on tbl1.ProductColorId = tbl4.ProductColorId
inner join DoDetail tbl5
on tbl3.DeliveryOrderDetailId = tbl5.DeliveryOrderId
inner join ProductMain tbl6
on tbl3.ProductId = tbl6.ProductId
inner join BPMain tbl7
on tbl5.BusinessPartnerId = tbl7.BusinessPartnerId
I have the query
select gltree.*,tsacc.confirm,tsacc.acc_no,commacc.* from tsacc
inner join commacc on tsacc.acc_no = commacc.acc_no and tsacc.glcode = commacc.glcode
inner join gltree on tsacc.glcode = gltree.glcode
where gltree.glcode = 12738
in this query two specified tables have 'glcode' column name , so
why I should specify table name in where clause eg. gltree.glcode and can't use only glcode without table name ? As we have just one glcode in executed query ?
You actually have threes columns with that name (tsacc.glcode, commacc.glcode and gltree.glcode), so you need to tell the database which one you mean.
The list of columns in the select list is evaluated as the last step when processing the statement. So when the DB processes the where clause it does not "know" which of them you are actually using (you could use all of them).
Plus: with an inner join it does indeed not matter, but if you were using an outer join it would make a big difference which of those three columns is used in the where clause.
I am trying to understand the following query which is automatically produced by some software library:
SELECT DISTINCT `t`.* FROM `teacher` AS `t`
LEFT JOIN `rel` AS `rel_profile`
ON `rel_profile`.`field_id` = 2319 AND `rel_profile`.`item_id` = `t`.`id`
LEFT JOIN `teacher_info` AS `profile`
ON `profile`.`id` = `rel_profile`.`related_item_id`
LEFT JOIN `rel` AS `rel_profile_city`
ON `rel_profile_city`.`field_id` = 2320 AND `rel_profile_city`.`item_id` = `profile`.`id` WHERE `rel_profile_city`.`item_id` = 1
There are three left joins. I understand the first and second one. What I don't understand is the third left join:
LEFT JOIN `rel` AS `rel_profile_city`
ON `rel_profile_city`.`field_id` = 2320 AND `rel_profile_city`.`item_id` = `profile`.`id` WHERE `rel_profile_city`.`item_id` = 1
The table rel has already been used in the first left join:
LEFT JOIN `rel` AS `rel_profile`
ON `rel_profile`.`field_id` = 2319
Now, the same table is left joined again but this time the value of the joined field is different:
LEFT JOIN `rel` AS `rel_profile_city`
ON `rel_profile_city`.`field_id` = 2320
How come that these two joins do not contradict?
The query is using aliases:
`rel` AS `rel_profile`
Says to pretend that the table rel is actually a table called rel_profile. That alias is then used throughout the rest of the query. I'm not sure of MySQL, but on some other database systems, it's an error to refer to the table as rel from then onwards(*) (unless there's another join that re-introduces the table and doesn't provide an alias).
And joining to the same table multiple times is allowed - provided that the names (or aliases) are unique. This is useful when you're trying to construct a result that relies on the content of multiple rows from the same table, where the result should occupy a single row.
(*) "Then onwards" being in the order in which the clauses are processed, not the text order. E.g. you should use the alias in the SELECT clause because, even though it occurs earlier textually, it's (conceptually) processed after the FROM clause.
This query will show teacher rows that have associated rows in rel with field_id = 2319 OR field_id = 2320
The are not "contradicting" each other. Imagine you have a table of users, wich have the demographic and personal data of your users. And another table with the "relation" between users. So, in this "relations" table, you have columns UserId1 and UserId2. If you want a query that returns the data of those two users, you'll need to do two JOINS with the table Users, once per each User column. This doesn't mean that they are contradicting each other.
I have a query which works, goes like this:
Select
count(InsuranceOrderLine.AntallPotensiale) as potensiale,
COUNT(InsuranceOrderLine.AntallSolgt) as Solgt,
InsuranceProduct.Name,
InsuranceProductCategory.Name as Kategori
From
InsuranceOrderLine, InsuranceProduct, InsuranceProductCategory
where
InsuranceOrderLine.FKInsuranceProductId = InsuranceProduct.InsuranceProductID
and InsuranceProduct.FKInsuranceProductCategory = InsuranceProductCategory.InsuranceProductCategoryID
Group by
InsuranceProduct.name, InsuranceProductCategory.Name
This query over returns what I need, but when I try to add more table (InsuranceOrder) to be able to get the regardingUser column, then all the count values are way high.
Select
count(InsuranceOrderLine.AntallPotensiale) as Potensiale,
COUNT(InsuranceOrderLine.AntallSolgt) as Solgt,
InsuranceProduct.Name,
InsuranceProductCategory.Name as Kategori,
RegardingUser
From
InsuranceOrderLine, InsuranceProduct, InsuranceProductCategory, InsuranceSalesLead
where
InsuranceOrderLine.FKInsuranceProductId = InsuranceProduct.InsuranceProductID
and InsuranceProduct.FKInsuranceProductCategory = InsuranceProductCategory.InsuranceProductCategoryID
Group by
InsuranceProduct.name, InsuranceProductCategory.Name,RegardingUser
Thanks in advance
You're adding one more table to your FROM statement, but you don't specify any JOIN condition for that table - so your previous result set will do a FULL OUTER JOIN (cartesian product) with your new table! Of course you'll get duplication of data....
That's one of the reasons that I'm recommending never to use that old, legacy style JOIN - do not simply list a comma-separated bunch of tables in your FROM statement.
Always use the new ANSI standard JOIN syntax with INNER JOIN, LEFT OUTER JOIN and so on:
SELECT
count(iol.AntallPotensiale) as Potensiale,
COUNT(iol.AntallSolgt) as Solgt,
ip.Name,
ipc.Name as Kategori,
isl.RegardingUser
FROM
dbo.InsuranceOrderLine iol
INNER JOIN
dbo.InsuranceProduct ip ON iol.FKInsuranceProductId = ip.InsuranceProductID
INNER JOIN
dbo.InsuranceProductCategory ipc ON ip.FKInsuranceProductCategory = ipc.InsuranceProductCategoryID
INNER JOIN
dbo.InsuranceSalesLead isl ON ???????? -- JOIN condition missing here !!
When you do this, you first of all see right away that you're missing a JOIN condition here - how is this new table InsuranceSalesLead linked to any of the other tables already used in this SQL statement??
And secondly, your intent is much clearer, since the JOIN conditions linking the tables are where they belong - right with the JOIN - and don't clutter up your WHERE clauses ...
It looks like you added the table join which slightly multiplies count of rows - make sure, that you properly joining the table. And be careful with aggregate functions over several joined tables - joins very often lead to duplicates