I have trouble. How to join 2 table query. if data table:
Table 1:
CustomerID : 1,2,3,4,5
Customercode : cus1,cus9,cus4,null,null
Customername: roya,almudena,jack,jane, Francisco
Table 2 :
CustomerID : 1,2,3,4
Customercode : cus1,cus2,cus9,null
Customername: roya,jose,almudena,jane
Q: what is query to show all name from 2 table (no duplicate name).
Thank you for your answer.
You don't need a JOIN for this, you need a UNION statement
select distinct name from table1
union
select distinct name from table2
if you use union all it will create duplicates, but union on its own will not.
you could wrap it in select distinct name from () as well if you want to be extra safe.
If you have no duplicate names within each table (as in your sample data), I strongly suggest:
select t1.customername
from table1 t1
union all
select t2.customername
from table2 t2
where not exists (select 1 from table1 t1 where t1.customername = t2.customername);
This should have better performance.
Use union statement :
select distinct Customername from table1
union
select distinct Customername from table2
Related
I have two tables in Access, one containing IDs (not unique) and some Name and one containing IDs (not unique) and Location. I would like to return a third table that contains only the IDs of the elements that appear more than 1 time in either Names or Location.
Table 1
ID Name
1 Max
1 Bob
2 Jack
Table 2
ID Location
1 A
2 B
Basically in this setup it should return only ID 1 because 1 appears twice in Table 1 :
ID
1
I have tried to do a JOIN on the tables and then apply a COUNT but nothing came out.
Thanks in advance!
Here is one method that I think will work in MS Access:
(select id
from table1
group by id
having count(*) > 1
) union -- note: NOT union all
(select id
from table2
group by id
having count(*) > 1
);
MS Access does not allow union/union all in the from clause. Nor does it support full outer join. Note that the union will remove duplicates.
Simple Group By and Having clause should help you
select ID
From Table1
Group by ID
having count(1)>1
union
select ID
From Table2
Group by ID
having count(1)>1
Based on your description, you do not need to join tables to find duplicate records, if your table is what you gave above, simply use:
With A
as
(
select ID,count(*) as Times From table group by ID
)
select * From A where A.Times>1
Not sure I understand what query you already tried, but this should work:
select table1.ID
from table1 inner join table2 on table1.id = table2.id
group by table1.ID
having count(*) > 1
Or if you have ID's in one table but not the other
select table1.ID
from table1 full outer join table2 on table1.id = table2.id
group by table1.ID
having count(*) > 1
How to get the result of select statement grouped by a column to perform join statement on it ?
You should enclose the select statement that contains the GROUP BY instead of one of the joined table, something like this:
SELECT t1.Id, ....
FROM Table1 t1
INNER JOIN
(
SELECT Id, COUNT(*)
FROM Table2
GROUP BY Id
) t2 ON t1.Id = t2.Table1Id
This might help you:
suppose there are two table
1.student
(stud_id pk)
(branch_id fk)
2. branch
(branch_id pk)
(branch name varchar)
(city varchar)
select * from student s,branch b where s.branch_id=b.branch_id group by b.city
I have
table1 : country, theOrderColumn1
table2 : country, theOrderColumn2
I want to join DISTINCT country from these two SELECT statements:
SELECT DISTINCT `country` FROM `table1` ORDER BY `theOrderColumn1`
and
SELECT DISTINCT `country` FROM `table2` ORDER BY `theOrderColumn2`
Example:
table1 (country, theOrderColumn1): (uk, 1), (usa, 2)
table2 (country, theOrderColumn2): (france, 1), (uk, 2)
I want this result:
france
uk
usa
select distinct country
from (
select country, theOrderColumn from table1
union all
select country, theOrderColumn from table2
) a
order by theOrderColumn
select country, theOrderColumn from (
select distinct t1.country as country, t1.theOrderColumn as theOrderColumn from table t1
union
select distinct t2.country as country, t2.theOrderColumn as theOrderColumn from table t2) t3
order by theOrderColumn
If you want to preserve order given by theOrderColumn1 and theOrderColumn2 at the same time, you can use the column index to specify the ORDER BY column.
SELECT DISTINCT country FROM (
(
SELECT country AS c, theOrderColumn1 AS d FROM table1
UNION
SELECT country AS c, theOrderColumn2 AS d FROM table2
) ORDER BY 2)
Take a look at the answers to this question: SQL Query - Using Order By in UNION
select a.country,a.theOrderColumn
(
select country,theOrderColumn
from table1
union
select country,theOrderColumn
from table2
) a
order by a.theOrderColumn
Though you will get duplicates if theOrderColumn is different in table 1 and table 2.
It depends on what you are wanting and how you want to join the two tables together. If you are joining based on "theOrderColumn", then the query would be
SELECT DISTINCT country
FROM table1
JOIN table2 ON table1.theOrderColumn = table2.theOrderColumn
ORDER BY theOrderColumn
If you want to join across country (which wouldn't make sense as the country would be identical in both tables) then you could swap out "country" in the join clause.
Also, depending on your SQL dialect spoken by your DBMS, your mileage may vary with the above query. Can you clarify more of what you are after?
I have something like the following structure: Table1 -> Table2 relationship is 1:m
I need to perform queries similar to the next one:
select Table1.id from Table1 left outer join Table2 on (Table1.id1 = Table2.id2) where Table2.name like '%a%' and rownum < 11
i.e. I want first 10 ids from Table 1 which fulfils conditions in Table2. The problem is that I've to use distinct, but the distinct clause applies after 'rownum < 11', so the result could be e.g. 5 records even if their number is more than 10.
The apparent solution is to use the following:
select id from ( select Table1.id from Table1 left outer join Table2 on (Table1.id1 = Table2.id2) where Table2.name like '%a%' ) where rownum < 11
But I'm afraid of performance of such a query. If Table1 contains about 300k records, and Table2 contains about 700k records, wouldn't such a query be really slow?
Is there another query, but without inner select? Unluckily, I want to avoid using inner selects.
Unluckily, I want to avoid using inner
selects
With having the WHERE clause on TABLE2, you are filtering the select to an INNER JOIN (ie. since Table2.name IS null <> Table2.name like '%a%' you will only get results where the join is INNER to one another. Also, the %a% without a function based index will result in a full table scan on each iteration.
but #lweller is completely correct, to do the query correctly you will need to use a subquery. keep in mind, without an ORDER BY you have no guarantee of the order of your top X records (it may always 'appear' that the values conform to the primary key or whatnot, but there is no guarantee.
WITH TABLE1 AS(SELECT 1 ID FROM DUAL
UNION ALL
SELECT 2 ID FROM DUAL
UNION ALL
SELECT 3 ID FROM DUAL
UNION ALL
SELECT 4 ID FROM DUAL
UNION ALL
SELECT 5 ID FROM DUAL) ,
TABLE2 AS(SELECT 1 ID, 'AAA' NAME FROM DUAL
UNION ALL
SELECT 2 ID, 'ABB' NAME FROM DUAL
UNION ALL
SELECT 3 ID, 'ACC' NAME FROM DUAL
UNION ALL
SELECT 4 ID, 'ADD' NAME FROM DUAL
UNION ALL
SELECT 1 ID, 'BBB' NAME FROM DUAL
) ,
sortable as( --here is the subquery
SELECT
Table1.ID ,
ROW_NUMBER( ) OVER (ORDER BY Table2.NAME NULLS LAST) ROWOverName , --this wil handle the sort
table2.name
from
Table1
LEFT OUTER JOIN --this left join it moot, pull the WHERE table2.name into the join to have it LEFT join as expected
Table2
on
(
Table1.id = Table2.id
)
WHERE
Table2.NAME LIKE '%A%')
SELECT *
FROM sortable
WHERE ROWOverName <= 2;
-- you can drop the ROW_NUMBER( ) analytic function and replace the final query as such (as you initially indicated)
SELECT *
FROM sortable
WHERE
ROWNUM <= 2
ORDER BY sortable.NAME --make sure to put in an order by!
;
You don't need DISTINCT here at all, and there is nothing bad in subqueries as such.
SELECT id
FROM Table1
WHERE id IN
(
SELECT id
FROM Table2
WHERE name LIKE '%a%'
)
AND rownum < 11
Note that the order is not guaranteed. To guarantee order, you have to use a nested query:
SELECT id
FROM (
SELECT id
FROM Table1
WHERE id IN
(
SELECT id
FROM Table2
WHERE name LIKE '%a%'
)
ORDER BY
id -- or whatever else
)
WHERE rownum < 11
There is no way to do it without nested queries (or the CTE).
For me there is no reason to be afraid of performance. I think the sub select ist the best way to solve your problem. And if you want don't trust me, take a look at explain plan of your query and you will see that it behave not so bad as you might think.
I have two tables with the same structure:
id name
1 Merry
2 Mike
and
id name
1 Mike
2 Alis
I need to union second table to first with keeping unique names, so that result is:
id name
1 Merry
2 Mike
3 Alis
Is it possible to do this with MySQL query, without using php script?
This is not a join (set multiplication), this is a union (set addition).
SELECT #r := #r + 1 AS id, name
FROM (
SELECT #r := 0
) vars,
(
SELECT name
FROM table1
UNION
SELECT name
FROM table2
) q
This will select all names from table1 and combine those with all the names from table2 which are not in table1.
(
select *
from table1
)
union
(
select *
from table2 t2
left join table1 t1 on t2.name = t1.name
where t1.id is null
)
Use:
SELECT a.id,
a.name
FROM TABLE_A a
UNION
SELECT b.id,
b.name
FROM TABLE_B b
UNION will remove duplicates.
As commented, it all depends on what your 'id' means, cause in the example, it means nothing.
SELECT DISTINCT(name) FROM t1 JOIN t2 ON something
if you only want the names
SELECT SUM(something), name FROM t1 JOIN t2 ON something GROUP BY name
if you want to do some group by
SELECT DISTINCT(name) FROM t1 JOIN t2 ON t1.id = t2.id
if the id's are the same
SELECT DISTINCT COALESCE(t1.name,t2.name) FROM
mytable t1 LEFT JOIN mytable t2 ON (t1.name=t2.name);
will get you a list of unique names from the 2 tables. If you want them to get new ids (like Alis does in your desired results), that's something else and requires the answers to a couple of questions:
do any of the names need to maintain their previous id. And if they do, which table's id should be preferred?
why do you have 2 tables with the same structure? ie what are you trying to accomplish when you generate the unique name list?