I want use select~~~~ subquery in case statement
but I Don't know how to do this
In my idea is
CASE When
(select ...from ... where .. )IS null
then ...
else ...
end as ...
but it's not working
You can do a temp table and query that
with
test as (select names from table where names=smith ) ---You can add in left
--joins here or whatever - again not sure what you are trying to accomplish
select Case when name=smith then "Yes" else Null end as Case_test
from test
Probably an easier way to do it with a subquery but off the top of my head I'm not sure. We would need more detail on what you were trying to accomplish but this would probably do the trick.
Related
I have this sql code where I try to display an alternative value as a result whenever the table is empty or the the single column of the top row when it is not
select top 1 case when count(*)!=0 then derrivedTable.primarykey
else 0 end endCase
from
(
select top 1 m.primarykey
from mytable m
where 0=1
)derrivedTable
The problem is that when I run this, I get the error message "column 'derrivedTable.primarykey' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause."
But when I put 'derrivedTable.primarykey' in the group by clause, I just get an empty table.
Does anyone hve a solution?
thanks in advance
You can use aggregation:
select coalesce(max(m.primarykey), 0)
from mytable m;
An aggregation query with no group by always returns exactly one row. If the table is empty (or all rows are filtered out), then the aggregation functions -- except for COUNT() -- return NULL -- which can be transformed to a value using COALESCE().
Such a construct makes me worry. If you are using this to set the primary key on an insert, then you should learn about identity columns or sequences. The database will do the work for you.
Can you try this below script-
SELECT
CASE
WHEN COUNT(*) = 1 THEN derrivedTable.primarykey
ELSE 0
END endCase
FROM
(
SELECT TOP 1 m.primarykey
FROM mytable m
WHERE 0 = 1
) derrivedTable
derrivedTable.primarykey;
I was trying to create a view and needed to create a column that shows if the 'somenumber' column exists on other table or not. The code below worked but very slowly. Is it possible to declare a table as (select someNumber from veryYugeTable) and check on that one instead of sending this query for every single record or using some other way to speed up the view?
case
when someOtherTable.someNumber in(select someNumber from veryYugeTable) then 'exists'
else 'doesn't exist'
end as "someColumn"
The query looks fine. You should have an index on veryYugeTable.someNumber.
Sometimes the optimizer handles correlated subqueries better than non-correlated ones, so you can try:
case
when exists
(
select *
from veryYugeTable
where veryYugeTable.someNumber = someOtherTable.someNumber
) then 'exists'
else 'doesn''t exist'
end as "someColumn"
(Well, as this query does exactly the same as yours, the optimizer should get to the same execution plan, but this is not always the case.)
But as mentioned: Make sure first to have that index.
You might find you get some benefit with scalar subquery caching if you do something like:
coalesce((select 'exists'
from veryyugetable vyt
where vyt.somenumber = someOtherTable.someNumber
and rownum = 1),
'doesn''t exist') somecolumn
N.B. the and rownum = 1 is not necessary if vyt.somenumber is a unique column. Also, I nth the suggest to index the vyt.somenumber column.
use left join instead of putting the in clause in select:
left join veryYugeTable on someNumber = someOtherTable.someNumber
adjust your case when statement as follow:
case
when veryYugeTable.OtherColumn is null then 'doesn''t exist'
else 'exist'
end as "someColumn"
I need to do this:
SELECT
COLUMN1,
COLUMN2,
CASE SOMETHING WHEN 0 THEN 'SOMETHING'
ELSE
CASE SOMETHING1 WHEN 'SOMETHING2' THEN (Here I need my value from other table)
ELSE
...
ELSE
...
END
END
AS SOMETHINGSPECIAL
...
...
...
Entire select is horribly complicated sorry.
In the place after THEN in () I need to take out specific value from other table.
I have tried almost everything there is from joins, to put there SELECT WHERE or CASE WHEN statement it always end up with some error.
Keyword missing etc.
Also maybe problem is inside () there is long concatenate:
''
I need to put that specific value from other table into that concatenate.
It either doesn't want to allow me to use other CASE WHEN after that THEN or I'm doing something wrong.
EDIT (sorry cant post entire query dont wanna have problems in work):
SELECT
A.SOMETHING
CASE WHEN A.LIST_ID IN ('something','something') THEN ' (MY VALUE FROM OTHER TABLE HERE) '
END
AS SOMETHINGSPECIAL
FROM SOMETABLE
...
(MY VALUE FROM OTHER TABLE HERE) I tried to put there Select statement condition, Case statement to take out that one value from other table but it just gives me error.
You can use a correlated subquery:
(CASE SOMETHING
WHEN 0 THEN 'SOMETHING'
ELSE (CASE SOMETHING1
WHEN 'SOMETHING2' THEN (select value from othertable ot where ot.col = x.col)
ELSE . . .
Do note that you don't need nested cases. You could write this as:
(CASE WHEN SOMETHING = 0 THEN 'SOMETHING'
WHEN SOMETHING1 = 'SOMETHING2' THEN (select value from othertable ot where ot.col = x.col)
ELSE . . .
END)
You could try joining the table that the other values should come from, that's if there is a link between those tables, so these is what you should do
SELECT
T1.COLUMN1,
T2.COLUMN1,
T.The-column-you-want-from-table2
iNNER JOIN TABLE2 T2 ON T2.cOUMN1 = T1.COLUMN1
So there is no need for a case statement, because from what I can gather from your question, you want a representation value of a value from another table
Here is another more specific example,
Select
Transaction.OrderId
Transaction.OrderDate
Order.StatusDescription
From Transaction
Inner Join Order on Order.OrderID = Transaction.OrderID
In the above example, the StatusDescription is what need from the "other" table, this can be anything from paid,out-of-stock or whatever status. This status in your first table is represented by a number like 1 for paid, 2 for out of stock etc.....
Hope this helps
Using Firebird:
I want to select a random entry in the table if the first SQL query returns 0 rows. Is there anyway to combine these two queries?
SELECT * FROM table WHERE cond=1;
SELECT FIRST 1 * FROM table ORDER BY rand();
Im using ExecuteNativeQuery on the java-side which takes basic SQL statements. Sadly, If-Else statements don't work. And if i could make a single query to the database instead of two, that would make my code appear faster.
try this: Not sure but think it will work...
Select FIRST 1 t1.*
FROM table t1
left Join Table t2
On t2.pk = t1.pk
And t2.cond=1
ORDER BY Case When t2.Cond = 1
Then 0 Else rand() End
if(exists(select 1 from table where cond=1))
SELECT * FROM table WHERE cond=1;
else
SELECT FIRST 1 * FROM table ORDER BY rand();
something like this, though I forgot whether the then keyword is needed in if statements in FirebirdSQL databases.
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I'm using a stored procedure in MySQL, with a CASE statement.
In the ELSE clause of the CASE ( equivalent to default: ) I want to select and return an empty result set, thus avoiding to throw an SQL error by not handling the ELSE case, and instead return an empty result set as if a regular query would have returned no rows.
So far I've managed to do so using something like:
Select NULL From users Where False
But I have to name an existing table, like 'users' in this example.
It works, but I would prefer a way that doesn't break if eventually the table name used is renamed or dropped.
I've tried Select NULL Where False but it doesn't work.
Using Select NULL does not return an empty set, but one row with a column named NULL and with a NULL value.
There's a dummy-table in MySQL called 'dual', which you should be able to use.
select
1
from
dual
where
false
This will always give you an empty result.
This should work on most DBs, tested on Postgres and Netezza:
SELECT NULL LIMIT 0;
T-SQL (MSSQL):
SELECT Top 0 1;
How about
SELECT * FROM (SELECT 1) AS TBL WHERE 2=3
Checked in myphp, and it also works in sqlite and probably in any other db engine.
This will probably work across all databases.
SELECT * FROM (SELECT NULL AS col0) AS inner0 WHERE col0 IS NOT NULL;
SELECT TOP 0 * FROM [dbo].[TableName]
This is a reasonable approach to constant scan operator.
SELECT NULL WHERE FALSE;
it works in postgresql ,mysql, subquery in mysql.
How about this?
SELECT 'MyName' AS EmptyColumn
FROM dual
WHERE 'Me' = 'Funny'
SELECT * FROM (SELECT NULL) WHERE 0
In PostgreSQL a simple
SELECT;
works. You won't even get any columns labeled 'unknown'.
Note however, it still says 1 row retrieved.