I need to left join a few tables in a query where the column names are ambiguous.
ListingCategory_Listings:
ID | ListingCategoryID | ListingID | ..
SiteTree_Live:
ID | ClassName | Title | Content | ..
ListingCategory:
ID | IconID
File:
ID | ClassName | Name | Title | Filename | ..
I have the query:
SELECT * FROM ListingCategory_Listings
LEFT JOIN Listing ON ListingCategory_Listings.ListingID = Listing.ID
LEFT JOIN SiteTree_Live ON Listing.ID = SiteTree_Live.ID
LEFT JOIN ListingCategory ON ListingCategory_Listings.ListingCategoryID = ListingCategory.ID
LEFT JOIN File ON ListingCategory.IconID = File.ID
Both the listing and listing category data is stored in the SiteTree_Live table, when my records are returned, obviously, the Title, ID, Content and other ambiguous fields are returned under the heading Title, ID, Content.
I need to access both the Listing Title and The Listing Category Title and other specific information. If they had their data stored in different tables I could use select Listing.Title AS lTitle but how can I do something similar in this situation?
You need to alias the columns and give them different labels.
You should always put only the fields you need into the SELECT clause, listing each individually rather than using *.
Good practice also dictates giving each table a short alias.
SELECT L.Title Listing_Title, LC.Title ListingCategory_Title,
... all your other columns ...
FROM ListingCategory_Listings LCL
LEFT JOIN Listing L ON LCL.ListingID = L.ID
LEFT JOIN SiteTree_Live STL ON L.ID = STL.ID
LEFT JOIN ListingCategory LC ON LCL.ListingCategoryID = LC.ID
LEFT JOIN File F ON LC.IconID = F.ID
I suggest that to ALIAS a COLUMN name, the previous information may not be correct.
The proper syntax for COLUMN ALIAS is :
SELECT column_name AS alias_name
FROM table_name;
In a COLUMN ALIAS, the COLUMN alias assignment is declared beside the proper COLUMN name.
The proper syntax for TABLE ALIAS is :
SELECT column_name(s)
FROM table_name AS alias_name;
In a TABLE ALIAS, the TABLE alias is put beside the column being selected in the SELECT portion of the statement. The TABLE ALAIS assignment is made in the FROM portion of the statement.
The difference being that the alias assignment is made beside the proper name of what is desired to be ALIASED!
I set up a practice on the Fraser's provided example & it worked for me. I believe the answer provided was speaking of TABLE ALIAS, not COLUMN ALIAS.
I disagree with ALIAS usage where the TABLE or COLUMN ALIAS is so short that it complicates the readability of the code. I believe it should be short, but not so short that the code is not 'self documenting' for maintenance purposes. That is my 2ยข of thought on it!
Related
Please who can help with this scenario?
I have two tables, both they have a common column ID, and Table 1 has a column Title. Normally I should update the content of this Title column for some ID, but since the table was already in use somewhere else, it wasn't a good idea to change data directly in Table 1.
That's why I created a new table table 2, which hold only the Title that must be changed associated with these ID that must be changed.
Now I am trying to get these updated titles from table 2, when there is a matching ID in table 1, otherwise show only the contents of table 1.
The result should be something like that but without using If statements.
__ID__ Title
| | | |
| | | |
You can use LEFT OUTER JOIN to this new table and COALESCE() function to say "If there is data in the new table, use it, otherwise use the data in the existing table" . Something like:
SELECT t1.id, COALESCE(t2.title, t1.title) as title
FROM t1
LEFT OUTER JOIN t2 ON t1.id = t2.id;
I have two hive SQL tables which consist of following columns.
table_1
|customer_id | ip_address|
region_table
|country_name | region_name|
I tried,
SELECT table_1.customer_id, table_1.ip_address, getCountry(ip_address) AS Country, region_table.region_name FROM table_1 JOIN region_table ON region_table.country_name = Country;
getCountry() is UDF which returns the country name when the IP address
is passed into it. I want to use that country name to create another
column with the corresponding region from the region_table. And i want
to get the following table as my output.
customer_id | ip_address | Country | region_name
Any thoughts on what I'm missing in my query?
select c.customer_id
,c.ip_address
,getCountry(c.ip_address) as Country
,r.region_name
from table_1 c
join region_table r
on r.country_name =
getCountry(c.ip_address)
In case of Oracle, you can not refer column alias defined in SELECT statement in WHERE clause of same query!! Because database engine first evaluates WHERE clause and identifies eligible rows and then proceeds to fetch columns as defined in SELECT part of query.
In your case, right query should be
select
table_1.customer_id,
table_1.ip_address,
getCountry(ip_address) AS Country,
region_table.region_name
FROM table_1
JOIN region_table ON region_table.country_name = getCountry(table_1 .ip_address);
I am trying to update field value from one table to another.
Item with bomRev='A' in Destination table look like show below
Same Item bomRev='A' in source table looks like
I want to update partid field in destination table for bomRev=A by the value in Source filed i want to destination looks exactly like the source.
I tried this but no luck
UPDATE [MIBOMD]
SET [MIBOMD].[partId] = [assy].[partId]
FROM [MIBOMD] INNER JOIN [assy] ON [MIBOMD].[partId] = [assy].[partId]
WHERE bomRev='A' and [bomItem]='600797' AND [MIBOMD].[partId]!=[assy].[partId];
UPDATE m
SET [partId] = a.[partId]
FROM
[MIBOMD] m
INNER JOIN
[assy] a
ON m.[bomItem] = a.[ItemId]
AND m.bomEntry = a.bomEntry
WHERE
m.bomRev='A'
AND m.[bomItem]='600797'
AND m.[partId]!=a.[partId];
You actually were pretty close! Just a couple of key differences. Before I explain I have used Table Aliases in the code I provided it is a shorthand way of referring to the table throughout the query that will make it a little easier to follow and read. To Alias a table after the table name in the from statement simply add a space and an alias or a space " AS " alias.
Now your Join as on partid in your version and that was your main issue. Because you want the records where partid are not the same so you can change the partid of the assy table. Looking at your dataset I was able to determine that the shared key was mibomd.bomItem and assy.ItemId. After clearing that up everything should be good.
Per your comment the only other thing that needed to be added was a second condition on the join to make it unique. [MIBOMD].bomEntry = assy.bomEntry
A little about join conditions. Typically you always want to figure out what the unique relationship between the 2 tables are (bomItem = ItemId and bomEntry = bomEntry) and that is what will go in the ON area of the join. Rarely that will be different and will be for very specific purposes.
Per your comment on how to insert the missing records
INSERT INTO MIBOMD (bomItem, bomRev, bomEntry, lineNbr, dType, partId)
SELECT
bomItem = a.ItemId
,bomRev = 'A' --or change the value to what you want
,a.bomEntry
,lineNbr = ???? --not sure how you are figure this out do if you wan it to be the next line number you can figure that out automatically if you need
,a.partId
FROM
assy a
LEFT JOIN MIBOMD m
ON a.ItemId = m.bomItem
AND a.bomEntry = m.bomEntry
WHERE
m.bomItem IS NULL
This time you would use a left join from assy to mibomd and figure out when they don't match mibomd.bomItem IS NULL
I have a little problem - since im not very experienced in SQL - about joining the same table on multiple values. Imagine there is table 1 (called Strings):
id value
1 value1
2 value2
and then there is table 2 (called Maps):
id name description
1 1 2
so name is reference into the Strings table, as is description. Without the second field referencing the Strings table it would be no problem, id just do an inner join on Strings.id = Maps.name. But now id like to obtain the actual string also for description. What would be the best approach for a SELECT that returns me both? Right now it looks like this:
SELECT Maps.id, Strings.value AS mapName FROM Maps INNER JOIN Strings ON Strings.id = Maps.name;
But that obviously only covers one of the localized names. Thank you in advance.
You can do this with two joins to the same table:
SELECT m.id, sname.value AS mapName, sdesc.value as description
FROM Maps m INNER JOIN
Strings sname
ON sname.id = m.name INNER JOIN
Strings desc
ON sdesc.id = m.description;
Note the use of table aliases to distinguish between the two tables.
As long as you want to get a single value from another table, you can use subqueries to do these lookups:
SELECT id,
(SELECT value FROM Strings WHERE id = Maps.name) AS name,
(SELECT value FROM Strings WHERE id = Maps.description) AS description
FROM Maps
Sorry if this is a basic question. I'm fairly new to SQL, so I guess I'm just missing the name of the concept to search for.
Quick overview.
First table (items):
ID | name
-------------
1 | abc
2 | def
3 | ghi
4 | jkl
Second table (pairs):
ID | FirstMember | SecondMember Virtual column (pair name)
-------------------------------------
1 | 2 | 3 defghi
2 | 1 | 4 abcjkl
I'm trying to build the virtual column shown in the second table
It could be built at the time any entry is made in the second table, but if done that way, the data in that column would get wrong any time one of the items in the first table is renamed.
I also understand that I can build that column any time I need it (in either plain requests or stored procedures), but that would lead to code duplication, since the second table can be involved in multiple different requests.
So is there a way to define a "virtual" column, that could be accessed as a normal column, but whose content is built dynamically?
Thanks.
Edit: this is on MsSql 2008, but an engine-agnostic solution would be preferred.
Edit: the example above was oversimplified in multiple ways - the major one being that the virtual column content isn't a straight concatenation of both names, but something more complex, depending on the content of columns I didn't described. Still, you've provided multiple paths that seems promising - I'll be back. Thanks.
You need to join the items table twice:
select p.id,
p.firstMember,
p.secondMember,
i1.name||i2.name as pair_name
from pairs as p
join items as i1 on p.FirstMember = i1.id
join items as i2 on p.SecondMember = i2.id;
Then put this into a view and you have your "virtual column". You would simply query the view instead of the actual pairs table wherever you need the pair_name column.
Note that the above uses inner joins, if your "FirstMember" and "SecondMember" columns might be null, you probably want to use an outer join instead.
You can use a view, which creates a table-like object from a query result, such as the one with a_horse_with_no_name provided.
CREATE VIEW pair_names AS
SELECT p.id,
p.firstMember,
p.secondMember,
CONCAT(i1.name, i2.name) AS pair_name
FROM pairs AS p
JOIN items AS i1 ON p.FirstMember = i1.id
JOIN items AS i2 ON p.SecondMember = i2.id;
Then to query the results just do:
SELECT id, pair_name FROM pair_names;
You could create a view for your 'virtual column', if you wanted to, like so:
CREATE VIEW aView AS
SELECT
p.ID,
p.FirstMember,
p.SecondMember,
a.name + b.name as 'PairName'
FROM
pairs p
LEFT JOIN
items a
ON
p.FirstMember = a.ID
LEFT JOIN
items b
ON
p.SecondMember = b.ID
Edit:
Or, of course, you could just use a similar select statement every time.
When selecting from tables you can name the results of a column using AS.
SELECT st.ID, st.FirstMember, st.SecondMember, ft1.Name + ft2.Name AS PairName
FROM Second_Table st
JOIN First_Table ft1 ON st.FirstMember = ft1.ID
JOIN First_Table ft2 ON st.SecondMember = ft2.ID
Should give you something like what you are after.