Bear with me. I'm new at this.
So, I have three queries, one after the other, the first two ending with semi-colons. It's the same data from the same tables but sliced three different ways. The 'ORDER-BY's are all the same. The results come out on three separate tabs. How do I combine the results into a single output?
Use the UNION or UNION ALL syntax and put the order by at the end
e.g
SELECT A, B
FROM X
UNION {ALL}
SELECT A, C
FROM Y
UNION {ALL}
SELECT D, E
FROM Z
order by 2;
Notes: UNION is usually a bit slower because it will remove duplicates from the results if more that one section returns the same row. UNION ALL will return all rows.
The data types for columns in each section must be the same.
Related
I am trying to display a combination of two tables in which all rows will be there from first table and only 1 row from second table on some condition.
I was using left join suggest me some solutions
I think what you are looking for is UNION or UNION ALL.
It basically appends the results of two queries.
So your query would look somewhat like
select a, b, c from oneTable
UNION ALL
select x, y, z from otherTable where id = 23
The individual select can have where clauses and all kinds of stuff you know from SQL.
I am building a website which populates from a database. I'm testing now, and I'd like to see what my site will look like with a lot of data (mainly so I can watch performance, build out pagination, and address any issues with presentation). I have about 10 pieces of data in my table, which is great, but I'd like to display about 2,000 on my page.
Is there a way I can read from the same SELECT * FROM table statement over and over again in the same query in order to read the table multiple times?
I can do this by feeding all my results into a variable and echoing that variable multiple times, but it won't allow me to set a LIMIT or give me the proper count of rows from the query.
I'm surprised I haven't found a way to do this by Googling. It seems like it would be an easy, built-in thing.
If there's not, can you suggest any other way I can do this without modifying my original table?
Please use Cross Join. Cross Join will give you a cartesian product of rows from tables joined. Cross Join can generate a lot of data in quick amount of time. Can be useful for extensive testing.
Example:
SELECT * FROM A
CROSS JOIN B;
You can cross join on the same table as well.
As of MySQL 8 you can use a recursive query to get your rows multifold:
with recursive cte (a, b, c) as
(
select a, b, 1 from mytable
union all
select a, b, c + 1 from cte where c < 10 -- ten times as many
)
select a, b from cte;
(You can of course alter the generated values in the part after union all, e.g.: select a + 5, b * 2, c + 1 from cte where c < 10.)
Demo: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=3a2699c167e1f4a7ffbe4e9b17ac7241
Forgive me if this seems like common sense as I am still learning how to split my data between multiple tables.
Basically, I have two:
general with the fields userID,owner,server,name
count with the fields userID,posts,topics
I wish to fetch the data from them and cannot decide how I should do it: in a UNION:
SELECT `userID`, `owner`, `server`, `name`
FROM `english`.`general`
WHERE `userID` = 54 LIMIT 1
UNION
SELECT `posts`, `topics`
FROM `english`.`count`
WHERE `userID` = 54 LIMIT 1
Or a JOIN:
SELECT `general`.`userID`, `general`.`owner`, `general`.`server`,
`general`.`name`, `count`.`posts`, `count`.`topics`
FROM `english`.`general`
JOIN `english`.`count` ON
`general`.`userID`=`count`.`userID` AND `general`.`userID`=54
LIMIT 1
Which do you think would be the more efficient way and why? Or perhaps both are too messy to begin with?
It's not about efficiency, but about how they work.
UNION just unions 2 different independent queries. So you get 2 result sets one after another.
JOIN appends each row from one result set to each row from another result set. So in total result set you have "long" rows (in terms of amount of columns)
Just for completeness as I don't think it's mentioned elsewhere: often UNION ALL is what's intended when people use UNION.
UNION will remove duplicates (so relatively expensive because it requires a sort). This remove duplicates in the final result (so it doesn't matter if there's a duplicate in a single query or the same data from individual SELECTs). UNION is a set operation.
UNION ALL just sticks the results together: no sorting, no duplicate removal. This is going to be quicker (or at least no worse) than UNION.
If you know the individual queries won't return duplicate results use UNION ALL. (In fact often best to assume UNION ALL and think about UNION if you need that behaviour; using SELECT DISTINCT with UNION is redundant).
You want to use a JOIN. Joining is used to creating a single set which is a combination of related data. Your union example doesn't make sense (and probably won't run). UNION is for linking two result sets with identical columns to create a set that has the combined rows (it does not 'union' the columns.)
If you want to fetch users and near user posts and topics. you need to write QUERY using JOIN like this:
SELECT general.*,count.posts,count.topics FROM general LEFT JOIN count ON general.userID=count.userID
Can anyone help me on how could I join two tables without merging the result into single row? Please see below query:
SELECT *
FROM resorderdetails rd
INNER JOIN resinvalidorderdetails ri
ON rd.itemid=ri.srcitemid;
Let say for example I have 1 row in resorderdetails table with field itemid=1 and I have 1 row in resinvalidorderdetails table with field srcitemid=1.
If we will going to execute the above query, it will return a result of single row [merging the data of two tables]
What I want to do is to have two rows as a result. The first row is the record came from resorderdetails and the other row is the record came from resinvalidorderdetails without using UNION ALL or UNION.
How could I do it? Is it possible?
It's not possible, because you wannna have :
SELECT * FROM resorderdetails rd
and
select * from resinvalidorderdetails
There are only joins operations and UNION which you don't want to use, and the JOINS will put together or remove commons ids and UNION will do exactly what you want
Beside to display a query with 2+ tables you need something in common(even the union need same number of columns).
I need to select records from 2 tables, one called cities and one called neighborhoods. They both share a table column in common called parent_state. In this cell the id of the parent state is stored.
I need to select all cities and neighborhoods that belong to a certain state. For example if the state id is 10, I need to get all the cities and neighborhoods that has this value for it's parent_state cell.
The state id is stored in a PHP variable like so:
$parent_state = '10';
What would this query look like (preferably the merged results from both tables should be sorted by the column name in alphabetical order)?
EDIT
Yes, I probably do need a union. I'm very new to mysql and all I can do at the moment is query tables individually.
I can always query both the cities and neighborhoods tables individually but the reason why I want to merge the results is for the sole purpose of listing said results alphabetically.
So can someone please show how the UNION query for this would look?
Use:
SELECT c.name
FROM CITIES c
WHERE c.parent_state = 10
UNION ALL
SELECT n.name
FROM NEIGHBORHOODS h
WHERE n.parent_state = 10
UNION ALL will return the result set as a combination of both queries as a single result set. UNION will remove duplicates, and is slower for it - this is why UNION ALL is a better choice, even if it's unlikely to have a city & neighbourhood with the same name. Honestly, doesn't sound like a good idea mixing the two, because a neighbourhood is part of a city...
Something else to be aware of with UNION is that there needs to be the same number of columns in the SELECT clause for all the queries being UNION'd (this goes for UNION and UNION ALL). IE: You'll get an error if the first query has three columns in the SELECT clause and the second query only had two.
Also, the data types have to match -- that means not returning a DATE/TIME data type in the same position was an other query returning an INTEGER.
What you want is probably not a join, but rather, a union. note that a union can only select the exact same columns from both of the joined expressions.
select * from city as c
inner join neighborhoods as n
on n.parent_state = c.parent_state
where c.parent_state=10
You can use Left,Right Join, in case of city and nighborhoods dont have relational data.