order multiple tables according to one column - mysql

Is it possible, using SQL to pull data from different tables, then sort the data according to one column that is in all tables. eg, I have 3 tables. Base, Selects, Sub. They all 3 have a position column,
Select base_layers.position, selects.position, subbases.position
from base_layers,selects,subbases
Order By (alls)position;
That is exactly what I actually want to do... But have a feeling it is not possible.


Use a union:
(I'm assuming you don't want to cross join all 3 tables)
select Position
from
(
select base_layers.position AS Position
from base_layers
union
select selects.position
from selects
union
select subbases.position
from subbases
) x
order by Position ASC;


Your syntax was incorrect. Try this version.
SELECT * FROM
(
SELECT base_layers.position
FROM base_layers
UNION ALL
SELECT selects.position
FROM selects
UNION ALL
SELECT subbases.position
FROM subbases
) tbl ORDER BY tbl.position;

Related

How to duplicate returning values from a query in MySQL

When I use this I Get the table two times but I want each value duplicated before the next value comes
SELECT *
FROM student
WHERE major LIKE 'C%'
UNION ALL
SELECT *
FROM student
WHERE major LIKE 'C%';

You can use a union all. A union will not work, because it will eliminate duplicates. Another way is a cross join:
select
*
from
students t1 cross join
(select 1 as n union all select 2) n
WHERE major LIKE 'C%'
order by id;

SQL search in the same order as requested and showing not found items

I want to do a special query for SQL but I'm not able to get the wanted result.
My basic query is:
select * from TABLE_NAME where COLUMN_NAME_1 in ('ABC1', 'ABC98', 'ABC97', 'ABC2', 'ABC3')
Imagine that the item 'ABC1' is not in the table. I would like my query to show it. In addition I would like that my query shows the items in the same order I asked (ABC1, ABC98, ABC97, and so on).
I attach an image where you'll understand better what I want.
Thanks in advance

You need to use an outer join or union all. One method looks like:
select v.col1, . . .
from (select 'ABC1' as col1, 1 as ord union all
select 'ABC98', 2 union all
. . .
) left join
TABLE_NAME t
on t.column_name_1 = v.col1
order by ord;
The exact syntax for the list of values varies by database. The above works for MySQL. Oracle would require from dual in the subqueries.

First of all you need a table of the values to show along with their desired position. You can create this on the fly in the FROM clause. Then outer join your table:
select keys.name, t.column_name_2, t.column_name_3, t.column_name_4
from
(
select 'ABC1' as name, 1 as sortkey
union all
select 'ABC98' as name, 2 as sortkey
union all
select 'ABC97' as name, 3 as sortkey
union all
select 'ABC2' as name, 4 as sortkey
union all
select 'ABC3' as name, 5 as sortkey
) as keys
left join table_name t on t.column_name_1 = keys.name
order by keys.sortkey;

Mysql Union in different columns

I have the following query
SELECT *
FROM(
(SELECT
MAX(c.start_time) as start_1
FROM
c1 c)
UNION ALL
(SELECT
MAX(cc.created_at) as ccmax
FROM
cc1)
) as t
I'd like to have the result in a table with 2 columns start_1 and cmax instead of the single column I get with all the different results listed.
How should I do it? I ended up in a subselect believing this would have done the job.

For the data to be in two columns you would have to use a sub select.
SELECT
MAX(c1.start_time) as start_1, (SELECT MAX(cc1.created_at) FROM cc1) as ccmax
FROM c1

mysql union statement with order by

I'am trying to understand what causes the following, maybe you could help me:
I have a query like:
select field1,fieldDate from table1
union all
select field1,fieldDate from table2
order by fieldDate desc
and the another one like this:
select field1,field2,fieldDate from table1
union all
select field1,field2,fieldDate from table2
order by fieldDate desc
So basically they are the same with the exception that in the second I retrieve an extra field.
Now, both results come with a diferent ordering, but just for the cases that the dates are exacly the same. For example there are 2 rows (row1,row2) with date 2009-11-25 09:41:55. For query 1 row1 comes before row2 and for query 2 row2 comes before row1.
Does somebody knows why this happens?
Thanks,
Regards

The ordering based on any fields that you don't explicitly order by is undefined, and the optimizer can change the ordering if it thinks that results in a better execution plan. Given two rows with the exact same value in the order by field you can not depend on them being in any particularly order in relation to each other unless you explicitly order by another field with different values.

Can you do this
select * from ( select
field1,field2,fieldDate, 0 as ordercol from table1
union all select
field1,field2,fieldDate, 1 as ordercol from table2) t1
order by fieldDate desc, ordercol asc

Straight from the MySQl manual, to user order by on a union you have to parenthesis the individual tables.
(select field1,fieldDate from table1)
union all
(select field1,fieldDate from table2)
order by fieldDate desc
This is not SQL standards compliant! The code you entered should order the union of both tables but to my surprise MySQL has the above syntax.
The order in which rows with the same fieldDate are returned can differ for each query execution. Usually this order will be the same but you should not count on it. If you want any extra ordering state more order by fields.

EDIT: This answer is wrong: the order by works on the entire union. I'll leave it here to save others the trouble :)
Your order by only works on the second part of the union. You can use a subquery to make the order by work on the entire union:
select field1,field2,fieldDate
from (
select field1,field2,fieldDate
from table1
union all
select field1,field2,fieldDate
from table2
) SubQueryName
order by fieldDate desc

How do I Concatenate entire result sets in MySQL?

I'm trying out the following query:
SELECT A,B,C FROM table WHERE field LIKE 'query%'
UNION
SELECT A,B,C FROM table WHERE field LIKE '%query'
UNION
SELECT A,B,C FROM table WHERE field LIKE '%query%'
GROUP BY B ORDER BY B ASC LIMIT 5
That's three queries stuck together, kinda sorta. However, the result set that comes back reflects results from query #3 before the results from query #1 which is undesired.
Is there any way to prioritize these so that results come as all for query #1, then all for query #2 then all for query #3? I don't want to do this in PHP just yet (not to mention having to control for results that showed up in the first query not to show in the second and so forth).

Maybe you should try including a fourth column, stating the table it came from, and then order and group by it:
SELECT A,B,C, "query 1" as origin FROM table WHERE field LIKE 'query%'
UNION
SELECT A,B,C, "query 2" as origin FROM table WHERE field LIKE '%query'
UNION
SELECT A,B,C, "query 3" as origin FROM table WHERE field LIKE '%query%'
GROUP BY origin, B ORDER BY origin, B ASC LIMIT 5

Add an additional column with hard-coded values that you will use to sort the overall resultset, like so:
SELECT A,B,C,1 as [order] FROM table WHERE field LIKE 'query%'
UNION
SELECT A,B,C,2 as [order] FROM table WHERE field LIKE '%query'
UNION
SELECT A,B,C,3 as [order] FROM table WHERE field LIKE '%query%'
GROUP BY B ORDER BY [order] ASC, B ASC LIMIT 5

Can you do it as a subselect, something like
SELECT * FROM (
SELECT A,B,C FROM table WHERE field LIKE 'query%'
UNION
SELECT A,B,C FROM table WHERE field LIKE '%query'
UNION
SELECT A,B,C FROM table WHERE field LIKE '%query%'
) ORDER BY B ASC LIMIT 5

SELECT distinct a,b,c FROM (
SELECT A,B,C,1 as o FROM table WHERE field LIKE 'query%'
UNION
SELECT A,B,C,2 as o FROM table WHERE field LIKE '%query'
UNION
SELECT A,B,C,3 as o FROM table WHERE field LIKE '%query%'
)
ORDER BY o ASC LIMIT 5
Would be my way of doing it. I dont know how that scales.
I don't understand the
GROUP BY B ORDER BY B ASC LIMIT 5
Does it apply only to the last SELECT in the union?
Does mysql actually allow you to group by a column and still not do aggregates on the other columns?
EDIT: aaahh. I see that mysql actually does. Its a special version of DISTINCT(b) or something. I wouldnt want to try to be an expert on that area :)

If there isn't a sort that makes sense to order them you desire, don't union the results together - just return 3 separate recordsets, and deal with them accordingly in your data tier.

I eventually (looking at all suggestions) came to this solution, its a bit of a compromise between what I need and time.
SELECT * FROM
(SELECT A, B, C, "1" FROM table WHERE B LIKE 'query%' LIMIT 3
UNION
SELECT A, B, C, "2" FROM table WHERE B LIKE '%query%' LIMIT 5)
AS RS
GROUP BY B
ORDER BY 1 DESC
it delivers 5 results total, sorts from the fourth "column" and gives me what I need; a natural result set (its coming over AJAX), and a wildcard result set following right after.
:)
/mp

There are two varients of UNION.
'UNION' and 'UNION ALL'
In most cases what you really want to say is UNION ALL as it does not do duplicate elimination (Think SELECT DISTINCT) between sets which can result in quite a bit of savings in terms of execution time.
Others have suggested multiple result sets which is a workable solution however I would caution against this in time sensitive applications or applications connected over WANs as doing so can result in significantly more round trips on the wire between server and client.

I don't understand why the need of union for taking the data from single table
SELECT A, B, C
FROM table
WHERE field LIKE 'query%'
OR field LIKE '%query'
OR field LIKE '%query%'
GROUP BY B
ORDER BY B ASC LIMIT 5