I'm working on an SQL project (involving a library database) and I'm having a hard time figuring out how to make a conditional count.
So, I have 4 tables: Imprumuturi, Cititori, Autori, Carti. I need to list the 'Cititori' that have more than one borrowed 'Carti' at the current time.
I tried to use
SELECT cititori.nume_cititor,COUNT(imprumuturi.pk_cititor)
AS numar_imprumuturi FROM cititori, imprumuturi
WHERE imprumuturi.data_return IS NULL GROUP BY cititori.nume_cititor
HAVING COUNT(imprumuturi.pk_cititor)>1
ORDER BY cititori.nume_cititor;
And while it lists all the 'Cititori", it doesn't count the number of active borrowed 'Carti' as it should.
Can I get a hint or some help on how to make it work?
These are the fields of my database
Seems you missed the relation between the tables:
SELECT cititori.nume_cititor,COUNT(imprumuturi.pk_cititor)
AS numar_imprumuturi
FROM cititori
INNER JOIN imprumuturi ON imprumuturi.pk_cititori = cititori.pk_cititori
WHERE imprumuturi.data_return IS NULL
GROUP BY cititori.nume_cititor
HAVING COUNT(imprumuturi.pk_cititor)>1
ORDER BY cititori.nume_cititor;
As suggested, you should not use the old implicit join syntax based on comma-separated table names and where condition, but use explicit join syntax.
Related
I am new to SQL and DB management. I am working on writing queries based on a schema which you can find below. This is an exercise for me to get familiar reading, writing queries on SQL Server for my job. Could you please help me out defining query based on the schema and simply explain the logic?
Thanks a lot!
SQL Server is my DBMS and here are the question
Display ID, First Name, Last Name, and Hits to display all players with more than 2000 career hits.
This one you can get by typing this query in Microsoft SQL Server
SELECT
MLB_PLAYERS.FIRST_NAME,
MLB_PLAYERS.LAST_NAME,
MLB_PLAYERS.ID,
CAREER_STATS.HITS
FROM
MLB_PLAYERS LEFT JOIN KEY_GAMES_STATS on MLB_PLAYERS.ID=CAREER_STATS.ID
WHERE
CAREER_STATS.HITS>2000
So you have a simple structure to follow:
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY
But you decide to get only 3 of them, which is select, from and where. By SELECT you decide which columns you wanna have as an output. Then in FROM you have to choose tables from which you wanna take your variables. But if you decide to use 2 different tables you need to join them. I used left join because I wanted to match hits to existing players. We can match them by similar key, in this case this is their ID. And eventually, you can use where to apply conditions to your queries
I guess you could do it with a join and a group
select p.MLB_PLAYERS.FIRST_NAME,
p.MLB_PLAYERS.LAST_NAME,
p.MLB_PLAYERS.ID,
count(g.KEY_GAMES_STATS.HITS) as hits
from MLB_PLAYERS p
left join KEY_GAMES_STATS on p.ID = g.ID -- not sure how to link there 2 tables
group by p.MLB_PLAYERS.FIRST_NAME,
p.MLB_PLAYERS.LAST_NAME,
p.MLB_PLAYERS.ID
having count(g.KEY_GAMES_STATS.HITS) > 2000
The query is:
I have a member table and a stage table, the 'band_name' is the foreign key in the members table.
I need to show the stage name (stage_name) and how many members will be performing on each stage.
I have attempted so far the following:
SELECT stage_name, member_ID,member.band_name
FROM stage, member
WHERE stage.stage_name = member.band_name
ORDER BY stage_name, member.band_name, member_ID;
This shows one stage_name and the three members but NOT as a number e.g.3 and none of the other stage_names
I think I may need to use COUNT and maybe also INNER join?
FYI - I am very new to SQL oracle
All help appreciated.
You need to learn proper, explicit, standard, readable JOIN syntax. Commas are history. JOIN is not only the future, but the present and much of the past as well.
Then, you want LEFT JOIN and GROUP BY:
SELECT stage_name, COUNT(m.member_ID)
FROM stage s LEFT JOIN
member m
ON s.stage_name = m.band_name
GROUP BY s.stage_name
ORDER BY s.stage_name;
I am trying to convert a T-SQL query to MS Access SQL and getting a syntax error that I am struggling to find. My MS Access SQL query looks like this:
INSERT INTO IndvRFM_PreSort (CustNum, IndvID, IndvRScore, IndRecency, IndvFreq, IndvMonVal )
SELECT
IndvMast.CustNum, IndvMast.IndvID, IndvMast.IndvRScore,
IndvMast.IndRecency, IndvMast.IndvFreq, IndvMast.IndvMonVal
FROM
IndvMast
INNER JOIN
OHdrMast ON IndvMast.IndvID = OHdrMast.IndvID
INNER JOIN
MyParameterSettings on 1=1].ProdClass
INNER JOIN
[SalesTerritoryFilter_Check all that apply] ON IndvMast.SalesTerr = [SalesTerritoryFilter_Check all that apply].SalesTerr
WHERE
(((OHdrMast.OrdDate) >= [MyParameterSettings].[RFM_StartDate]))
GROUP BY
IndvMast.CustNum, IndvMast.IndvID, IndvMast.IndvRScore,
IndvMast.IndRecency, IndvMast.IndvFreq, IndvMast.IndvMonVal,
[CustTypeFilter_Check all that apply].IncludeInRFM,
[ProductClassFilter_Check all that apply].IncludeInRFM,
[SourceCodeFilter_Check all that apply].IncludeInRFM,
IndvMast.FlgDontUse
I have reviewed differences between MS Access SQL and T-SQL at http://rogersaccessblog.blogspot.com/2013/05/what-are-differences-between-access-sql.html and a few other locations but with no luck.
All help is appreciated.
update: I have removed many lines trying to find the syntax error and I am still getting the same error when running just (which runs fine using T-SQL):
SELECT
IndvMast.CustNum, IndvMast.IndvID, IndvMast.IndvRScore,
IndvMast.IndRecency, IndvMast.IndvFreq, IndvMast.IndvMonVal
FROM
IndvMast
INNER JOIN
OHdrMast ON IndvMast.IndvID = OHdrMast.IndvID
INNER JOIN
[My Parameter Settings] ON 1 = 1
There are a number of items in your query that should also have failed in any SQL-compliant database:
You have fields from tables in GROUP BY not referenced in FROM or JOIN clauses.
Number of fields in SELECT query do not match number of fields in INSERT INTO clause.
The MyParameterSettings table is not properly joined with valid ON expression.
Strictly MS Access SQL items:
For more than one join, MS Access SQL requires paired parentheses but even this can get tricky if some tables are joined together and their paired result joins to outer where you get nested joins.
Expressions like ON 1=1 must be used in WHERE clause and for cross join tables as MyParameterSettings appears to be, use comma-separated tables.
For above reasons and more, it is advised for beginners to this SQL dialect to use the Query Design builder providing table diagrams and links (if you have the MS Access GUI .exe of course). Then, once all tables connect graphically with at least one field selected, jump into SQL view for any nuanced scripting logic.
Below is an adjustment to SQL statement to demonstrate the parentheses pairings and for best practices, uses table aliases especially with long table names.
INSERT INTO IndvRFM_PreSort (CustNum, IndvID, IndvRScore, IndRecency, IndvFreq, IndvMonVal)
SELECT
i.CustNum, i.IndvID, i.IndvRScore, i.IndRecency, i.IndvFreq, i.IndvMonVal
FROM
[MyParameterSettings] p, (IndvMast i
INNER JOIN
OHdrMast o ON i.IndvID = o.IndvID)
INNER JOIN
[SalesTerritoryFilter_Check all that apply] s ON i.SalesTerr = s.SalesTerr
WHERE
(o.OrdDate >= p.[RFM_StartDate])
GROUP BY
i.CustNum, i.IndvID, i.IndvRScore, i.IndRecency, i.IndvFreq, i.IndvMonVal
And in your smaller SQL subset, the last table does not need an ON 1=1 condition and may be redundant as well in SQL Server. Simply a comma separate table will suffice if you intend for cross join. The same is done in above example:
SELECT
IndvMast.CustNum, IndvMast.IndvID, IndvMast.IndvRScore,
IndvMast.IndRecency, IndvMast.IndvFreq, IndvMast.IndvMonVal
FROM
[My Parameter Settings], IndvMast
INNER JOIN
OHdrMast ON IndvMast.IndvID = OHdrMast.IndvID
I suppose there are some errors in your query, the first (more important).
Why do you use HAVING clause to add these conditions?
HAVING (((IndvMast.IndRecency)>(date()-7200))
AND (([CustTypeFilter_Check all that apply].IncludeInRFM)=1)
AND (([ProductClassFilter_Check all that apply].IncludeInRFM)=1)
AND (([SourceCodeFilter_Check all that apply].IncludeInRFM)=1)
AND ((IndvMast.FlgDontUse) Is Null))
HAVING usually used about conditions on aggregate functions (COUNT, SUM, MAX, MIN, AVG), for scalar value you must put in WHERE clause.
The second: You have 12 parenthesis opened and 11 closed in HAVING clause
I have the following query:
CREATE TABLE Professor_Average
SELECT Instructor, SUM( + instreffective_avg + howmuchlearned_avg + instrrespect_avg)/5
FROM instreffective_average, howmuchlearned_average, instrrespect_average
GROUP BY Instructor;
It is telling me that Instructor is ambiguous. How do I fix this?
Qualify instructor with the name of the table it came from.
For example: instreffective_average.Instructor
If you don't do this, SQL will guess which table of the query it came from, but if there are 2 or more possibilities it doesn't try to guess and tells you it needs help deciding.
Your query most likely fails in more than one way.
In addition to what #Patashu told you about table-qualifying column names, you need to JOIN your tables properly. Since Instructor is ambiguous in your query I am guessing (for lack of information) it could look like this:
SELECT ie.Instructor
,SUM(ie.instreffective_avg + h.howmuchlearned_avg + ir.instrrespect_avg)/5
FROM instreffective_average ie
JOIN howmuchlearned_average h USING (Instructor)
JOIN instrrespect_average ir USING (Instructor)
GROUP BY Instructor
I added table aliases to make it easier to read.
This assumes that the three tables each have a column Instructor by which they can be joined. Without JOIN conditions you get a CROSS JOIN, meaning that every row of every table will be combined with every row of every other table. Very expensive nonsense in most cases.
USING (Instructor) is short syntax for ON ie.Instructor = h.Instructor. It also collapses the joined (necessarily identical) columns into one. Therefore, you would get away without table-qualifying Instructor in the SELECT list in my example. Not every RDBMS supports this standard-SQL feature, but you failed to provide more information.
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
INNER JOIN versus WHERE clause — any difference?
What is the difference between an INNER JOIN query and an implicit join query (i.e. listing multiple tables after the FROM keyword)?
For example, given the following two tables:
CREATE TABLE Statuses(
id INT PRIMARY KEY,
description VARCHAR(50)
);
INSERT INTO Statuses VALUES (1, 'status');
CREATE TABLE Documents(
id INT PRIMARY KEY,
statusId INT REFERENCES Statuses(id)
);
INSERT INTO Documents VALUES (9, 1);
What is the difference between the below two SQL queries?
From the testing I've done, they return the same result. Do they do the same thing? Are there situations where they will return different result sets?
-- Using implicit join (listing multiple tables)
SELECT s.description
FROM Documents d, Statuses s
WHERE d.statusId = s.id
AND d.id = 9;
-- Using INNER JOIN
SELECT s.description
FROM Documents d
INNER JOIN Statuses s ON d.statusId = s.id
WHERE d.id = 9;
There is no reason to ever use an implicit join (the one with the commas). Yes for inner joins it will return the same results. However, it is subject to inadvertent cross joins especially in complex queries and it is harder for maintenance because the left/right outer join syntax (deprecated in SQL Server, where it doesn't work correctly right now anyway) differs from vendor to vendor. Since you shouldn't mix implicit and explict joins in the same query (you can get wrong results), needing to change something to a left join means rewriting the entire query.
If you do it the first way, people under the age of 30 will probably chuckle at you, but as long as you're doing an inner join, they produce the same result and the optimizer will generate the same execution plan (at least as far as I've ever been able to tell).
This does of course presume that the where clause in the first query is how you would be joining in the second query.
This will probably get closed as a duplicate, btw.
The nice part of the second method is that it helps separates the join condition (on ...) from the filter condition (where ...). This can help make the intent of the query more readable.
The join condition will typically be more descriptive of the structure of the database and the relation between the tables. e.g., the salary table is related to the employee table by the EmployeeID column, and queries involving those two tables will probably always join on that column.
The filter condition is more descriptive of the specific task being performed by the query. If the query is FindRichPeople, the where clause might be "where salaries.Salary > 1000000"... thats describing the task at hand, not the database structure.
Note that the SQL compiler doesn't see it that way... if it decides that it will be faster to cross join and then filter the results, it will cross join and filter the results. It doesn't care what is in the ON clause and whats in the WHERE clause. But, that typically wont happen if the on clause matches a foreign key or joins to a primary key or indexed column. As far as operating correctly, they are identical; as far as writing readable, maintainable code, the second way is probably a little better.
there is no difference as far as I know is the second one with the inner join the new way to write such statements and the first one the old method.
The first one does a Cartesian product on all record within those two tables then filters by the where clause.
The second only joins on records that meet the requirements of your ON clause.
EDIT: As others have indicated, the optimization engine will take care of an attempt on a Cartesian product and will result in the same query more or less.
A bit same. Can help you out.
Left join vs multiple tables in SQL (a)
Left join vs multiple tables in SQL (b)
In the example you've given, the queries are equivalent; if you're using SQL Server, run the query and display the actual exection plan to see what the server's doing internally.