I want to make a query that simply makes this, this may sound really dumb but i made a lot of research and couldn't understand nothing.
Imagine that i have two tables (table1 and table2) and two columns (table1.column1 and table2.column2).
What i want to make is basically this:
SELECT column1 FROM table1 where table2.column2 = '0'
I don't know if this is possible.
Thanks in advance,
You need to apply join between two talbes and than you can apply your where clause will do work for you
select column1 from table1
inner join table2 on table1.column = table2.column
where table2.columne=0
for join info you can see this
Reading this original article on The Code Project will help you a lot: Visual Representation of SQL Joins.
Find original one at: Difference between JOIN and OUTER JOIN in MySQL.
SELECT column1 FROM table1 t1
where exists (select 1 from table2 t2
where t1.id = t2.table1_id and t2.column2 = '0')
assuming table1_id in table2 is a foreign key refering to id of table1 which is the primary key
You don't have any kind of natural join between two tables.
You're asking for
Select Houses.DoorColour from Houses, Cars where Cars.AreFourWheelDrive = '1'
You'd need to think about why you're selecting anything from the first table, there must be a shared piece of information between tables 1 and 2 otherwise a join is pointless and probably dangerous.
Related
I want to perform an inner join on a table, based on it's values, like this:
SELECT table2.value FROM table1
INNER JOIN table2 ON table2.key IN (table1.value)
WHERE table1.key = 'test'
Something with the in () is not working, the "in (table1.value)" is not being interpret as "in ('1','2')", it does not show any results.
table1:
KEY VALUE
test '1','2'
table2:
KEY VALUE
1 result1
2 result2
3 result3
I know there is a workaround like this, but I'd like to solve this without an additional SELECT..
SELECT * FROM table2 WHERE table2.value in (SELECT value FROM table1 WHERE key = 'test')
Any ideas?
Thanks,
Lennart
First, your data structure is simply wrong. You should not be storing lists of ids in a string. There are numerous good reasons:
SQL does not have good string processing functions.
You should not store integers as strings.
You should declare proper foreign key relationships.
Your queries cannot take advantage of indexes or partitioning.
The right solution is one row per key and per value.
However, sometimes, we are stuck with other people's really bad design decisions. In that case, you can use like:
SELECT table2.value
FROM table1 t1 INNER JOIN
table2 t2
ON t1.value LIKE '%''' + t2.key + '''%'
WHERE t1.key = 'test';
I am trying to write an SQL query that will return Table1, which has 10 columns. This table consists of a primary key id, 4 foreign key Id columns, and 5 other columns that I want to return but not change. The goal is to do a join to replace the foreign key Ids with their descriptions that are held in other tables.
Here is one attempt with the first FK Id:
Select * from Table1 t1
left join Table2 t2
on t1.BranchId = t2.BranchId;
This left join returns the description from table2, but does not replace it.
Here is another with the first FK Id:
Select t2.BranchName from Table1 t1
left join Table2 t2
on t1.BranchId = t2.BranchId;
This returns the name I want, but does not return table1 fully.
For the sake of an example you could pretend that OtherName3, OtherName4, OtherName5 are in tables Table3, Table4, Table5, respectively.
This may seem trivial for experienced SQL devs, but I am having a hard time figuring out the syntax.
Thanks!
I'm not sure what you mean by replace it.
I think you just need to list out all the columns you want:
Select t1.col1, t1.col2, t1.col3, . . .,
t2.name
from Table1 t1 left join
Table2 t2
on t1.BranchId = t2.BranchId;
I don't know what you mean by 'replace' but you just need to qualify what columns from which table you want. That goes for all tables you are joined to, especially if they have the same column name in multiple tables. I put junk columns in since I don't know your tables but you should get the general idea.
Select t2.BranchName, t1.BranchId, t1.Name, t1.Amount, t2.BranchLocation from Table1 t1
left join Table2 t2
on t1.BranchId = t2.BranchId;
I think this is what you are looking for:
select t1.*, t2.BranchName from Table1 t1
left join Table2 t2
on t1.BranchId = t2.BranchId;
Return Table1 fully (all columns) and only the description (BranchName) from Table2.
If using SQL Server, see all syntax options for the SELECT clause here:
https://msdn.microsoft.com/en-us/library/ms176104.aspx
I can't seem to ever remember this query!
I want to delete all rows in table1 whose ID's are the same as in Table2.
So:
DELETE table1 t1
WHERE t1.ID = t2.ID
I know I can do a WHERE ID IN (SELECT ID FROM table2) but I want to do this query using a JOIN if possible.
DELETE t1
FROM Table1 t1
JOIN Table2 t2 ON t1.ID = t2.ID;
I always use the alias in the delete statement as it prevents the accidental
DELETE Table1
caused when failing to highlight the whole query before running it.
DELETE Table1
FROM Table1
INNER JOIN Table2 ON Table1.ID = Table2.ID
There is no solution in ANSI SQL to use joins in deletes, AFAIK.
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Later edit
Other solution (sometimes performing faster):
DELETE FROM Table1
WHERE EXISTS( SELECT 1 FROM Table2 Where Table1.id = Table2.id)
PostgreSQL implementation would be:
DELETE FROM t1
USING t2
WHERE t1.id = t2.id;
Try this:
DELETE Table1
FROM Table1 t1, Table2 t2
WHERE t1.ID = t2.ID;
or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I think that you might get a little more performance if you tried this
DELETE FROM Table1
WHERE EXISTS (
SELECT 1
FROM Table2
WHERE Table1.ID = Table2.ID
)
This will delete all rows in Table1 that match the criteria:
DELETE Table1
FROM Table2
WHERE Table1.JoinColumn = Table2.JoinColumn And Table1.SomeStuff = 'SomeStuff'
Found this link useful
Copied from there
Oftentimes, one wants to delete some records from a table based on criteria in another table. How do you delete from one of those tables without removing the records in both table?
DELETE DeletingFromTable
FROM DeletingFromTable INNER JOIN CriteriaTable
ON DeletingFromTable.field_id = CriteriaTable.id
WHERE CriteriaTable.criteria = "value";
The key is that you specify the name of the table to be deleted from as the SELECT. So, the JOIN and WHERE do the selection and limiting, while the DELETE does the deleting. You're not limited to just one table, though. If you have a many-to-many relationship (for instance, Magazines and Subscribers, joined by a Subscription) and you're removing a Subscriber, you need to remove any potential records from the join model as well.
DELETE subscribers, subscriptions
FROM subscribers INNER JOIN subscriptions
ON subscribers.id = subscriptions.subscriber_id
INNER JOIN magazines
ON subscriptions.magazine_id = magazines.id
WHERE subscribers.name='Wes';
Deleting records with a join could also be done with a LEFT JOIN and a WHERE to see if the joined table was NULL, so that you could remove records in one table that didn't have a match (like in preparation for adding a relationship.) Example post to come.
Since the OP does not ask for a specific DB, better use a standard compliant statement.
Only MERGE is in SQL standard for deleting (or updating) rows while joining something on target table.
merge table1 t1
using (
select t2.ID
from table2 t2
) as d
on t1.ID = d.ID
when matched then delete;
MERGE has a stricter semantic, protecting from some error cases which may go unnoticed with DELETE ... FROM. It enforces 'uniqueness' of match : if many rows in the source (the statement inside using) match the same row in the target, the merge must be canceled and an error must be raised by the SQL engine.
To Delete table records based on another table
Delete From Table1 a,Table2 b where a.id=b.id
Or
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I often do things like the following made-up example. (This example is from Informix SE running on Linux.)
The point of of this example is to delete all real estate exemption/abatement transaction records -- because the abatement application has a bug -- based on information in the real_estate table.
In this case last_update != nullmeans the account is not closed, and res_exempt != 'p' means the accounts are not personal property (commercial equipment/furnishings).
delete from trans
where yr = '16'
and tran_date = '01/22/2016'
and acct_type = 'r'
and tran_type = 'a'
and bill_no in
(select acct_no from real_estate where last_update is not null
and res_exempt != 'p');
I like this method, because the filtering criteria -- at least for me -- is easier to read while creating the query, and to understand many months from now when I'm looking at it and wondering what I was thinking.
Referencing MSDN T-SQL DELETE (Example D):
DELETE FROM Table1
FROM Tabel1 t1
INNER JOIN Table2 t2 on t1.ID = t2.ID
This is old I know, but just a pointer to anyone using this ass a reference. I have just tried this and if you are using Oracle, JOIN does not work in DELETE statements.
You get a the following message:
ORA-00933: SQL command not properly ended.
While the OP doesn't want to use an 'in' statement, in reply to Ankur Gupta, this was the easiest way I found to delete the records in one table which didn't exist in another table, in a one to many relationship:
DELETE
FROM Table1 as t1
WHERE ID_Number NOT IN
(SELECT ID_Number FROM Table2 as t2)
Worked like a charm in Access 2016, for me.
delete
table1
from
t2
where
table1.ID=t2.ID
Works on mssql
Back in the old days, I used to write select statements like this:
SELECT
table1.columnA, table2.columnA
FROM
table1, table2
WHERE
table1.columnA = 'Some value'
However I was told that having comma separated table names in the "FROM" clause is not ANSI92 compatible. There should always be a JOIN statement.
This leads to my problem.... I want to do a comparison of data between two tables but there is no common field in both tables with which to create a join. If I use the 'legacy' method of comma separated table names in the FROM clause (see code example), then it works perfectly fine. I feel uncomfortable using this method if it is considered wrong or bad practice.
Anyone know what to do in this situation?
Extra Info:
Table1 contains a list of locations in 'geography' data type
Table2 contains a different list of 'geography' locations
I am writing select statement to compare the distances between the locations. As far I know you cant do a JOIN on a geography column??
You can (should) use CROSS JOIN. Following query will be equivalent to yours:
SELECT
table1.columnA
, table2.columnA
FROM table1
CROSS JOIN table2
WHERE table1.columnA = 'Some value'
or you can even use INNER JOIN with some always true conditon:
FROM table1
INNER JOIN table2 ON 1=1
Cross join will help to join multiple tables with no common fields.But be careful while joining as this join will give cartesian resultset of two tables.
QUERY:
SELECT
table1.columnA
, table2,columnA
FROM table1
CROSS JOIN table2
Alternative way to join on some condition that is always true like
SELECT
table1.columnA
, table2,columnA
FROM table1
INNER JOIN table2 ON 1=1
But this type of query should be avoided for performance as well as coding standards.
A suggestion - when using cross join please take care of the duplicate scenarios. For example in your case:
Table 1 may have >1 columns as part of primary keys(say table1_id,
id2, id3, table2_id)
Table 2 may have >1 columns as part of primary keys(say table2_id,
id3, id4)
since there are common keys between these two tables (i.e. foreign keys in one/other) - we will end up with duplicate results. hence using the following form is good:
WITH data_mined_table (col1, col2, col3, etc....) AS
SELECT DISTINCT col1, col2, col3, blabla
FROM table_1 (NOLOCK), table_2(NOLOCK))
SELECT * from data_mined WHERE data_mined_table.col1 = :my_param_value
I have a database with two tables that are similar to:
table1
------
Id : long, auto increment
Title : string(50)
ParentId : long
table2
------
Id : long, auto increment
FirstName : string(20)
LastName : string(30)
Zip : string(5)
table2 has a one-to-many relationship with table1 where many includes zero.
I also have the following query (that works correctly, so ignore typos an the like, it is an example):
SELECT t1.Id AS tid, t1.Title, t2.Id AS oid, t2.FirstName, t2.LastName
FROM table t1
INNER JOIN table2 t2 ON t1.ParentId = t2.Id
WHERE t2.Id IN
(SELECT Id FROM table2
WHERE Zip IN ('zip1', 'zip2', 'etc'))
ORDER BY t2.Id DESC
The query finds all items in table1 that belong to a person in table2, where the person is in one of the listed zip codes.
The problem I have now is: I want to show all the users (with their items if available) in the listed zip codes, not just the ones with items.
So, I am wondering, should I just do something simple with a lot more queries, like:
SELECT Id AS oid, FirstName, LastName FROM table2 WHERE Zip in ('zip1', 'zip2', 'etc')
foreach(result) {
SELECT Id AS tid, Title FROM table2 WHERE ParentId = oid
}
Or should I come up with a more elaborate single SQL statement? And if so, can I get a little help? Thanks!
If I understand correctly, changing your INNER JOIN to a RIGHT JOIN should return all users regardless of whether they have an item or not, the item columns will just be null for those that don't.
Look into Right Joins and Group By. That will most likely get you the query you are after.
I agree with (and have upvoted) #Lee D and #Bueller. However, I generally advocate LEFT OUTER JOINS, because I find it easier to conceptualized what's going on with them, particularly when you are joining three or more tables. Consider it like so:
Start with what you know you want in the final result set:
FROM table2 t2
and then add in the "optional" data.
FROM table2 t2
left outer join table1 t1
on t1.ParentId = t2.Id
Whether or not matches are found, whatever gets selected from table2 will always appears.
In general, you should prefer the "many queries" approach if (and only if)
it gets you simpler code in total
is fast enough (which you should find out by testing)
In this case, I suspect, both conditions may not apply.
You should come up with a more elaborate single SQL statement and then process the results with your favorite programming language.
What you've described is called an N + 1 query. You have 1 initial query that returns N results, then 1 query for each of your N results. If N is small, the performance difference may not be noticeable - but there will be a larger and larger performance hit as N grows.
If I understand correctly, I think you are looking for something like this
SELECT t1.Id AS tid, t1.Title, t2.Id AS oid, t2.FirstName, t2.LastName
FROM table t1
RIGHT OUTER JOIN table2 t2 ON t1.ParentId = t2.Id AND Zip IN ('zip1', 'zip2', 'etc'))
ORDER BY t2.Id DESC
You can have multiple conditions on your JOIN and RIGHT OUTER will give you all the rows in table2 even if they don't match in table1