I have 2 tables. The first has a structure like
id (int)
parent_id (int)
category_name (varchar)
The second has a structure like:
id (int)
old_category (int)
new_category (int)
I want to make a query to pull the old category and new category names all in one query for the parents. That is, I want to get the name of the old parent, then get the name of the new parent. The second table contains a historical list of all the parent ID changes made in the first table. How can I do this? Thanks!
SELECT old_cat.category_name, new_cat.category_name
FROM join_table
LEFT JOIN category_table as old_cat
ON old_cat.id = join_table.old_category
LEFT JOIN category_table as new_cat
ON new_cat.id = join_table.new_category;
If you've managed to get this far, it's time to stop coding and start learning MySQL JOIN Syntax.
SELECT
t.id,
t.old_category,
oc.category_name as old_category_name,
t.new_catevory,
nc.category_name as new_category_name
FROM
table1 t
INNER JOIN table2 oc on oc.id = t.old_category
INNER JOIN table2 nc on nc.id = t.new_category
I would seriously consider some modifications in column names, btw. To start: why don't the categories in table2 have an id postfix?
I will take a guess at what you meant:
tblOne
id
cat_name
tblTwo
id
tblOneId (old_cat) int
new_cat int
select * from tblOne t1, tblTwo t2 Where t1.id = t2.tblOneId
Join them?
select * from table1
join table2 j1 on table2.id = table1.old_category
join table2 j2 on table2.id = table1.new_category
Related
How can I join three or four SQL tables that DO NOT have an equal amount of rows while ensuring that there are no duplicates of a primary/foreign key?
Structure:
Table1: id, first_name, last_name, email
Table2: id (independent of id in table 1), name, location, table1_id, table2_id
Table3: id, name, location
I want all of the data from table 1, then all of the data from table 2 corresponding with the table1_id without duplicates.
Kind of tricky for a new guy...
Not sure what do you want to do with Table3.
A LEFT JOIN returns all records from the LEFT table, and the matched records from the right table. If there is no match (from the right side), then the result is NULL.
So per example:
SELECT * FROM Table1 AS t
LEFT JOIN Table2 AS tt
ON t.id = tt.id
The LEFT table refers to the table statement before the LEFT JOIN, and the RIGHT table refers to the table statement after the LEFT JOIN. If you want to add in Table3 as well, use the same logic:
SELECT * FROM Table1 AS t
LEFT JOIN Table2 AS tt
ON t.id = tt.id
LEFT JOIN Table3 AS ttt
ON t.id = ttt.id
Note, that I use alias names for the tables (by using AS), so that I can more easily refer to a specific table. For example, t refers to Table1, tt refers to Table2, and ttt refers to Table3.
Joins are often used in SQL, therefore it is useful to look into: INNER JOIN, RIGHT JOIN, FULL JOIN, and SELF JOIN, as well.
Hope this helps.
Good luck with learning!
You will want to use an LEFT JOIN
SELECT * FROM table1 LEFT JOIN table2 ON Table1.ID = Table2.table1_id
I have two tables in my database, one holds the names of files, and other holds records of information described in them, inincluding sizes of sections. it can be descrived as:
Table1: id as integer, name as varchar
Table2: recid as integer primary key, file_id as integer, score as float
Between the tables there is an one-to-many link, from Table1.id to table2.file_id. What i need is for every file which name matches a certain pattern retrieve the id of the linked record with the maximum score and the score itself.
So far i have used:
SELECT name,MAX(score)
FROM Table1
LEFT OUTER JOIN Table2 ON Table2.file_id=Table1.id
WHERE name LIKE :pattern
GROUP BY name
but i cannot retrieve the id of the record in Table2 this way.
The dialect i am using is Sqlite.
What query should be used to retrieve data on the record that has maximum score for every file?
Update:
With this query, i am getting close to what i want:
SELECT name,score,recid
FROM Table1
LEFT OUTER JOIN Table2 ON file_id=id
WHERE name LIKE :pattern
GROUP BY name
HAVING score=MAX(score)
However, this leaves out the entries in the first table that have no corresponding entries in the second table out. How can i ensure they are in the end result anyway? Should i use UNION, and if so - how?
This can actually be achieved without a GROUP BY by using a brilliantly simple technique described by #billkarwin here:
SELECT name, t2.score
FROM Table1 t1
LEFT OUTER JOIN Table2 t2 ON t2.file_id = t1.id
LEFT OUTER JOIN Table2 t2copy ON t2copy.file_id = t2.file_id
AND t2.score < t2copy.score
WHERE name LIKE :pattern
AND t2copy.score IS NULL
See SQL Fiddle demo.
I think that you must use a subquery
SELECT name, recid, score
FROM Table1
LEFT OUTER JOIN Table2 ON Table2.file_id=Table1.id
WHERE name LIKE :pattern AND score = (SELECT MAX(score) FROM Table2.score)
I think the easiest way to do this is with a correlated subquery:
SELECT name, recid, score
FROM Table1 LEFT OUTER JOIN
Table2
ON Table2.file_id=Table1.id
WHERE name LIKE :pattern AND
score = (SELECT MAX(t2.score)
FROM Table1 t1 LEFT OUTER JOIN
Table2 t2
ON t2.file_id=t1.id
where t1.name = table1.name
);
Note that you need table aliases to distinguish the tables in the inner query from the outer query. I am guessing which tables the columns are actually coming from.
I have several tables that I am joining that I need to add another table to and I can't seem to get the right query. Here is what I have now -
Table 1
carid, catid, makeid, modelid, caryear
Table 2
makeid, makename
Table 3
modelid, modelname
Table 4
catid, catname
The query I am using to join these is:
SELECT * FROM table1 a
JOIN table2 b on a.makeid=b.makeid
JOIN table3 c on a.modelid=c.modelid
JOIN table4 d on a.catid=d.catid
WHERE a.carid = $carid;
Now I need to add a 5th table that I am getting from a 3rd party that I am having a hard time adding to my existing query. The new table has these fields -
Table 5
id, year, make, model, citympg, hwympg
I need the citympg and hwympg based on caryear from table 1, makename from table 2, and modelname from table 3. I know I can do a second query with those values, but I would prefer to do a single query and have all of the data in a single row. Can this be done in a single query? If so, how?
it's possible to have more than condition in a join.
does this work?
SELECT a.*, e.citympg, e.hwympg
FROM table1 a
JOIN table2 b on a.makeid=b.makeid
JOIN table3 c on a.modelid=c.modelid
JOIN table4 d on a.catid=d.catid
Join table5 e on b.makename = e.make
and c.modelname = e.model
and a.caryear = e.year
WHERE a.carid = $carid;
...though your question is not clear. Did you only want to join table5 to the others, or was there something else you wanted to do with table5?
Without indexes, It won't be efficient, but you can do
LEFT JOIN table5 ON (table2.make = table5.make AND table3.model = table5.model AND table1.caryear = table5.caryear)
This also assumes the make and models and years strings match exactly.
Is there any way to name the complete select as a table? I will try to explain what I am trying to do. I have this
SELECT
*
FROM
`Databse1`.`table1`
JOIN
`Database2`.`table2`
ON
`table2`.`customerID` = `table1`.`customerID`
WHERE
`table1`.`recordID` IN (1,2,3,4)
I have another table, table3 that has these fields
customerID
recordID
the recordID is foreign key to table1.
What I want to do is in above query somehow enter customerID so
it can get all the recordIDs. Is that possible?
Sounds like you want a derived table
SELECT
*
FROM Table3 t3
JOIN (SELECT
*
FROM `Databse1`.`table1`
JOIN `Database2`.`table2` ON `table2`.`customerID` = `table1`.`customerID`
WHERE
`table1`.`recordID` IN (1,2,3,4)) t1 ON t1.customerID = t3.customerID
WHERE t3.customerID = [your customer id]
Here is my situation:
Table one contains a set of data that uses an id for an unique identifier. This table has a one to many relationship with about 6 other tables such that.
Given Table 1 with Id of 001:
Table 2 might have 3 rows with foreign key: 001
Table 3 might have 12 rows with foreign key: 001
Table 4 might have 0 rows with foreign key: 001
Table 5 might have 28 rows with foreign key: 001
I need to write a report that lists all of the rows from Table 1 for a specified time frame followed by all of the data contained in the handful of tables that reference it.
My current approach in pseudo code would look like this:
select * from table 1
foreach(result) {
print result;
select * from table 2 where id = result.id;
foreach(result2) {
print result2;
}
select * from table 3 where id = result.id
foreach(result3) {
print result3;
}
//continued for each table
}
This means that the single report can run in the neighbor hood of 1000 queries. I know this is excessive however my sql-fu is a little weak and I could use some help.
LEFT OUTER JOIN Tables2-N on Table1
SELECT Table1.*, Table2.*, Table3.*, Table4.*, Table5.*
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.ID = Table2.ID
LEFT OUTER JOIN Table3 ON Table1.ID = Table3.ID
LEFT OUTER JOIN Table4 ON Table1.ID = Table4.ID
LEFT OUTER JOIN Table5 ON Table1.ID = Table5.ID
WHERE (CRITERIA)
Join doesn't do it for me. I hate having to de-tangle the data on the client side. All those nulls from left-joining.
Here's a set-based solution that doesn't use Joins.
INSERT INTO #LocalCollection (theKey)
SELECT id
FROM Table1
WHERE ...
SELECT * FROM Table1 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table2 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table3 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table4 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table5 WHERE id in (SELECT theKey FROM #LocalCollection)
Ah! Procedural! My SQL would look like this, if you needed to order the results from the other tables after the results from the first table.
Insert Into #rows Select id from Table1 where date between '12/30' and '12/31'
Select * from Table1 t join #rows r on t.id = r.id
Select * from Table2 t join #rows r on t.id = r.id
--etc
If you wanted to group the results by the initial ID, use a Left Outer Join, as mentioned previously.
You may be best off to use a reporting tool like Crystal or Jasper, or even XSL-FO if you are feeling bold. They have things built in to handle specifically this. This is not something the would work well in raw SQL.
If the format of all of the rows (the headers as well as all of the details) is the same, it would also be pretty easy to do it as a stored procedure.
What I would do: Do it as a join, so you will have the header data on every row, then use a reporting tool to do the grouping.
SELECT * FROM table1 t1
INNER JOIN table2 t2 ON t1.id = t2.resultid -- this could be a left join if the table is not guaranteed to have entries for t1.id
INNER JOIN table2 t3 ON t1.id = t3.resultid -- etc
OR if the data is all in the same format you could do.
SELECT cola,colb FROM table1 WHERE id = #id
UNION ALL
SELECT cola,colb FROM table2 WHERE resultid = #id
UNION ALL
SELECT cola,colb FROM table3 WHERE resultid = #id
It really depends on the format you require the data in for output to the report.
If you can give a sample of how you would like the output I could probably help more.
Join all of the tables together.
select * from table_1 left join table_2 using(id) left join table_3 using(id);
Then, you'll want to roll up the columns in code to format your report as you see fit.
What I would do is open up cursors on the following queries:
SELECT * from table1 order by id
SELECT * from table1 r, table2 t where t.table1_id = r.id order by r.id
SELECT * from table1 r, table3 t where t.table1_id = r.id order by r.id
And then I would walk those cursors in parallel, printing your results. You can do this because all appear in the same order. (Note that I would suggest that while the primary ID for table1 might be named id, it won't have that name in the other tables.)
Do all the tables have the same format? If not, then if you have to have a report that can display the n different types of rows. If you are only interested in the same columns then it is easier.
Most databases have some form of dynamic SQL. In that case you can do the following:
create temporary table from
select * from table1 where rows within time frame
x integer
sql varchar(something)
x = 1
while x <= numresults {
sql = 'SELECT * from table' + CAST(X as varchar) + ' where id in (select id from temporary table'
execute sql
x = x + 1
}
But I mean basically here you are running one query on your main table to get the rows that you need, then running one query for each sub table to get rows that match your main table.
If the report requires the same 2 or 3 columns for each table you could change the select * from tablex to be an insert into and get a single result set at the end...