I have an sql statement like this:
Select Id,Name From table where id = var
Select Id,Name From table where id = var
Select Id,Name From table where id = var
I was able to a multiple select in one query but it's only allows one column per select.
SELECT (
SELECT COUNT(*)
FROM user_table
) AS tot_user,
(
SELECT COUNT(*)
FROM cat_table
) AS tot_cat,
(
SELECT COUNT(*)
FROM course_table
) AS tot_course
Use join if tables relates each other else
use union.
You can use any of subselects, unions or joins - it depends on what you're trying to do:
SQL joins are used to query data from two or more tables, based on a relationship between certain columns in these tables.
For instance:
SELECT user_table.name, user_table.email, cat_table.title
FROM user_table
FULL JOIN cat_table
ON user_table.cat_id=cat_table.id
ORDER BY user_table.id
More to read at http://www.w3schools.com/sql/sql_join.asp
Related
I am wondering if there is any way to save the intermediate result or tables in SQL. For example assume you have two different SQL statements that in the first statement you join two tables, then you want to see how many rows the resulting table has. I know there are many ways to do this but I am interested in seeing how this can be done sequentially. Consider the following example:
select * from order_table left join customer_table on order_table.id = customer_table.id
Then I want to see count of number of rows (as an easy example)
select count(*) from table
But I do not know what this table should be. How may I save the result of above query in some logical table or how to refer to what was created before in SQL.
You can use WITH like below:
WITH resultTable as ( select * from order_table left join customer_table on order_table.id = customer_table.id )
select count(*) from resultTable
For this particular example you can simply wrap the original query in a sub-query:
select count(*)
from (
select *
from order_table
left join customer_table on order_table.id = customer_table.id
) as x
If you want to store the result in a physical table (temporary or permanent) then the procedure varies for each rdbms. In SQL Server for example you would use SELECT INTO:
select *
into #temp_table
from order_table
left join customer_table on order_table.id = customer_table.id
you can also use CTE. for your question it will be:
;
with table1 as (
select * from order_table
left join customer_table on order_table.id = customer_table.id
)
select count(*) from table1
GO
How can I create a query to SELECT ALL DB WITHOUT duplicates
Like (old DB that is no longer in use c,f,g. basically if it does have eur and has an original name than it is relevant):
a
b
c
ceur
d
f
feur
g
geur
I need it to be like:
a
b
ceur
d
feur
geur
Many thanks...
SELECT DISTINCT
is what you're looking for. See more here.
For instance, let's say you have a table that contains the following rows:
name, city, address, country.
You now wish to get the countries that has been stored, without duplicates. Multiple people might come from the same country, and so the table would most likely have duplicate entries of that country.
How you achieve this is by using the SELECT DISTINCT.
Example:
SELECT DISTINCT country FROM table_name;
What this will do is retreive the country row without duplicates. That way, you can see which countries are actually stored in that table without duplicates.
If you have multiple databases (I don't know if that's what you were getting at), then you will need to perform a JOIN on the relevant tables, given you have access to them all. I would recommend doing a LEFT JOIN if you are to join more than just 1 extra table.
Example:
SELECT DISTINCT table_name.row_name, table_name.row_name2, table_name.row_name3
FROM table_name
LEFT JOIN table_name2 ON table_name.row_name = table_name2.row_name
LEFT JOIN table_name3 ON table_name2.row_name = table_name3.row_name
[...]
WHERE table.row_name = 'value';
Can you query information_schema.TABLES and distinct in the select, plus a predicate to filter out whatever you don't want?
You can do:
select t.*
from t
where name like '%eur'
union all
select t.*
from t
where not like '%eur' and
not exists (select 1 from t t2 where t2.name = concat(t.name, 'eur');
Is it possible to combine a result of two cte to another cte. I wrote a query combining two cte. The result gave a three column data in which I want to group the third column and averaging the second column. The second column resulted from a case sum statement.
If you are asking whether you can re-use CTEs after they have been used in a query, the answer is no. You can't do this:
with A
as (
-- query
)
select A.*
from A;
-- this is a separate query
select id
, count(*)
from A
group by
id
You can, however, combine CTEs in all kinds of ways, as long as you do it in a single statement. You can do this, which uses the hypothetical CTE A in two CTEs and the final query:
with A
as (
-- some query
)
, ACustomers
as (
select *
from Customers
join A
on ....
)
, AVendors
as (
select *
from Vendors
join A
on ....
)
select A.StateId
, ACount = COUNT(*)
, CustomerCount = (select count(*) from ACustomers ac where ac.StateId = A.StateId )
, VendorCount = (select count(*) from AVendors av where av.StateId = A.StateId )
from A
group by
A.StateId
I want to extract some information from two different table in one database,
[(first table): id-nbrNight-........]
[(second table): id-........]
I want to extract the nbrNight from the first table & the id from the second table:
so in my case I write this, but I don't know how to rassemble this two line in one line:
SELECT sum(nbrNight) as night FROM firsttab
SELECT count(`id`) as id FROM secondtab
I wirte this to rassemble this two line:
SELECT sum(nbrNight) as night,count(`id`) FROM firsttab,secondtab
But it doesn't work!
You can use UNION to combine the result from two query like
SELECT sum(nbrNight) as night FROM firsttab
UNION
SELECT count(`id`) as id FROM secondtab
(OR) do a JOIN with both tables using a common column between them (if any present) like below (assuming id is the common column between them)
SELECT sum(t1.nbrNight) as nightsum, count(t2.`id`) as idcount
FROM firsttab t1 JOIN secondtab t2 ON t1.id = t2.id
One option is to use the queries as inline views; reference those queries as a rowsource (like a table) in another query.
Since each query returns a single row, you can safely perform a JOIN operation, without need for any join predicate (aka CROSS JOIN).
For example:
SELECT f.night
, s.id
FROM ( SELECT SUM(nbrNight) AS night FROM firsttab ) f
CROSS
JOIN ( SELECT COUNT(id) AS id FROM secondtab ) s
Another option (since both queries are guaranteed to return exactly one row, if they don't return an error) is to include the query in the SELECT list of another query. It's not necessary to include a column alias in the subquery, but we can assign an alias.
For example:
SELECT ( SELECT SUM(nbrNight) FROM firsttab ) AS night
, ( SELECT COUNT(id) FROM secondtab ) AS id
If either of the queries were returning more than one column, then the approach in the first example will still work. The inline view queries can return multiple expressions, and we can reference those expressions in the outer query. With the pattern in the second example, that imposes a restriction that the subqueries must return only one expression (one column).
As an example to demonstrate an inline view returning more than one column, the inline view f returns three expressions:
SELECT f.night
, f.cnt
, f.min_nbr
, s.id
FROM ( SELECT SUM(nbrNight) AS night
, COUNT(nbrNight) AS cnt
, MIN(nbrNight) AS min_nbr
FROM firsttab
) f
CROSS
JOIN ( SELECT COUNT(id) AS id FROM secondtab ) s
I have a list of ids and need to check whether user with id is in DB or not in one SELECT. Like SELECT WHERE IN (). But SELECT WHERE IN () doesn't suit my needs, I need in one SELECT distinguish those ids that are in table, and those that are not, not using any loops like multiple SELECTS. Any ideas are welcome!
I'm not sure if this is what you need, but I guess you have table 1 which contains a lot of IDs, and you would like to see which ones occur in table 2 and which ones don't?
select T1.ID, count(*) 'Times of occurrences in T2'
from table 1 T1
left outer join table 2 T2
ON T1.ID = T2.ID
group by T1.ID
You should provide more details. Would it be a single query so a list could be hardcoded into query or you want to find general solution for any list of ids provided? How long is your list?
For single query and not very long list you can use union. On example:
SELECT some_value, EXISTS( SELECT 1 FROM tableName WHERE user_id = some_value )
UNION ALL
SELECT other_value, EXISTS( SELECT 1 FROM tableName WHERE user_id = other_value )
UNION ALL
SELECT other_value2, EXISTS( SELECT 1 FROM tableName WHERE user_id = other_value2 )
UNION ALL
.....
If your list of ids can vary and/or consists of thousands of records it is impossible. In list you have columnar layout and you want to change it to row-level results. In MsSQL there are PIVOT, UNPIVOT clauses which can do that. In MySQL such transformation without explicit unions are impossible.