How to Check whether a table contains rows or not sql server 2005?
For what purpose?
Quickest for an IF would be IF EXISTS (SELECT * FROM Table)...
For a result set, SELECT TOP 1 1 FROM Table returns either zero or one rows
For exactly one row with a count (0 or non-zero), SELECT COUNT(*) FROM Table
Also, you can use exists
select case when exists (select 1 from table)
then 'contains rows'
else 'doesnt contain rows'
end
or to check if there are child rows for a particular record :
select * from Table t1
where exists(
select 1 from ChildTable t2
where t1.id = t2.parentid)
or in a procedure
if exists(select 1 from table)
begin
-- do stuff
end
Like Other said you can use something like that:
IF NOT EXISTS (SELECT 1 FROM Table)
BEGIN
--Do Something
END
ELSE
BEGIN
--Do Another Thing
END
FOR the best performance, use specific column name instead of * - for example:
SELECT TOP 1 <columnName>
FROM <tableName>
This is optimal because, instead of returning the whole list of columns, it is returning just one. That can save some time.
Also, returning just first row if there are any values, makes it even faster. Actually you got just one value as the result - if there are any rows, or no value if there is no rows.
If you use the table in distributed manner, which is most probably the case, than transporting just one value from the server to the client is much faster.
You also should choose wisely among all the columns to get data from a column which can take as less resource as possible.
Can't you just count the rows using select count(*) from table (or an indexed column instead of * if speed is important)?
If not then maybe this article can point you in the right direction.
Fast:
SELECT TOP (1) CASE
WHEN **NOT_NULL_COLUMN** IS NULL
THEN 'empty table'
ELSE 'not empty table'
END AS info
FROM **TABLE_NAME**
Related
I have a trigger in SQL Server that needs to check on an update the number of rows with a value between a certain amount and do something accordingly. My current code is something like this:
IF EXISTS(SELECT COUNT(id) as NumberOfRows
FROM database
WHERE id = 3 AND value <= 20 and value > 2
GROUP BY id
HAVING COUNT(id) > 18)
-- if true, do something
From what I can tell, the select statement should find the number of rows with a value between 2 and 20 and if there are more than 18 rows, the EXISTS function should return 1 and the query will execute the code within the IF statement.
However, what is happening is that it is always executing the code within the IF statement regardless of the number of rows with a value between 2 and 20.
Any ideas on why this might be? I can post more complete code if it might help.
The reason is that the Exists function is checking the result of the sub-query for existing - are there any rows or not. And, as you return the COUNT, it'll never be not-existing - COUNT returns 0 if there are no rows presented in database.
Try to store the resulting count in a local variable, like in this question:
Using IF ELSE statement based on Count to execute different Insert statements
DECLARE #retVal int
SELECT #retVal = COUNT(*)
FROM TABLE
WHERE COLUMN = 'Some Value'
IF (#retVal > 0)
BEGIN
--INSERT SOMETHING
END
ELSE
BEGIN
--INSERT SOMETHING ELSE
END
I would do it like so (single line):
IF ((SELECT COUNT(id) FROM table WHERE ....)>18) BEGIN
...do something
You can even do between in a single line
IF ((SELECT COUNT(id) FROM table WHERE ....)between 2 and 20) BEGIN
...do something
END
Your subquery is looking for matches in the entire table. It does not limit the results only to those that are related to the rows affected by the update. Therefore, if the table already has rows matching your condition, the condition will be true on any update that affects other rows.
In order to count only the relevant rows, you should either join the database table to the inserted pseudo-table or use just the inserted table (there is not enough information in your question to be sure which is better).
I have a valid SQL select which returns an empty result, up and until a specific transaction has taken place in the environment.
Is there something available in SQL itself, that will allow me to return a 0 as opposed to an empty dataset? Similar to isNULL('', 0) functionality. Obviously I tried that and it didn't work.
PS. Sadly I don't have access to the database, or the environment, I have an agent installed that is executing these queries so I'm limited to solving this problem with just SQL.
FYI: Take any select and run it where the "condition" is not fulfilled (where LockCookie='777777777' for example.) If that condition is never met, the result is empty. But at some point the query will succeed based on a set of operations/tasks that happen. But I would like to return 0, up until that event has occurred.
You can store your result in a temp table and check ##rowcount.
select ID
into #T
from YourTable
where SomeColumn = #SomeValue
if ##rowcount = 0
select 0 as ID
else
select ID
from #T
drop table #T
If you want this as one query with no temp table you can wrap your query in an outer apply against a dummy table with only one row.
select isnull(T.ID, D.ID) as ID
from (values(0)) as D(ID)
outer apply
(
select ID
from YourTable
where SomeColumn = #SomeValue
) as T
alternet way is from code, you can check count of DataSet.
DsData.Tables[0].Rows.count > 0
make sure that your query matches your conditions
Debugging an app which queries SQL Server 05, can't change the query but need to optimise things.
Running all the selects seperately are quick <1sec, eg: select * from acscard, select id from employee... When joined together it takes 50 seconds.
Is it better to set uninteresting accesscardid fields to null or to '' when using EXISTS?
SELECT * FROM ACSCard
WHERE NOT EXISTS
( SELECT Id FROM Employee
WHERE Employee.AccessCardId = ACSCard.acs_card_number )
AND NOT EXISTS
( SELECT Id FROM Visit
WHERE Visit.AccessCardId = ACSCard.acs_card_number )
ORDER by acs_card_id
Do you have indexes on Employee.AccessCardId, Visit.AccessCardId, and ACSCard.acs_card_number?
The SELECT clause is not evaluated in an EXISTS clause. This:
WHERE EXISTS(SELECT 1/0
FROM EMPLOYEE)
...should raise an error for dividing by zero, but it won't. But you need to put something in the SELECT clause for it to be a valid query - it doesn't matter if it's NULL or a zero length string.
In SQL Server, NOT EXISTS (and NOT IN) are better than the LEFT JOIN/IS NULL approach if the columns being compared are not nullable (the values on either side can not be NULL). The columns compared should be indexed, if they aren't already.
I use a cursor to iterate through quite a big table. For each row I check if value from one column exists in other.
If the value exists, I would like to increase value column in that other table.
If not, I would like to insert there new row with value set to 1.
I check "if exists" by:
IF (SELECT COUNT(*) FROM otherTabe WHERE... > 1)
BEGIN
...
END
ELSE
BEGIN
...
END
I don't know how to get that row which was found and update value. I don't want to make another select.
How can I do this efficiently?
I assume that the method of checking described above isn't good for this case.
Depending on the size of your data and the actual condition, you have two basic approaches:
1) use MERGE
MERGE TOP (...) INTO table1
USING table2 ON table1.column = table2.column
WHEN MATCHED
THEN UPDATE SET table1.counter += 1
WHEN NOT MATCHED SOURCE
THEN INSERT (...) VALUES (...);
the TOP is needed because when you're doing a huge update like this (you mention the table is 'big', big is relative, but lets assume truly big, +100MM rows) you have to batch the updates, otherwise you'll overwhelm the transaction log with one single gigantic transaction.
2) use a cursor, as you are trying. Your original question can be easily solved, simply always update and then check the count of rows updated:
UPDATE table
SET column += 1
WHERE ...;
IF ##ROW_COUNT = 0
BEGIN
-- no match, insert new value
INSERT INTO (...) VALUES (...);
END
Note that this approach is dangerous though because of race conditions: there is nothing to prevent another thread from inserting the value concurrently, so you may end up with either duplicates or a constraint violation error (preferably the latter...).
This is just psuedo code because I have no idea of your table structure but I think you will understand... basically Update the columns you want then Insert the columns you need. A Cursor operation sounds unnecessary.
Update OtherTable
Set ColumnToIncrease = ColumnToIncrease + 1
FROM CurrentTable Where ColumnToCheckValue is not null
Insert Into OtherTable (ColumnToIncrease, Field1, Field2,...)
SELECT
1,
?
?
FROM CurrentTable Where ColumnToCheckValue is not null
Without a sample, I think this is the best I can do. Bottom line: you don't need a cursor. UPDATE where a match exists (INNER JOIN) and INSERT where one does not.
UPDATE otherTable
SET IncrementingColumn = IncrementingColumn + 1
FROM thisTable INNER JOIN otherTable ON thisTable.ID = otherTable.ID
INSERT INTO otherTable
(
ID
, IncrementingColumn
)
SELECT ID, 1
FROM thisTable
WHERE NOT EXISTS (SELECT *
FROM otherTable
WHERE thisTable.ID = otherTable.ID)
I think you'd be better off using a view for this -- then it's always up to date, no risk of mistakenly double/triple/etc counting:
CREATE VIEW vw_value_count AS
SELECT st.value,
COUNT(*) AS numValue
FROM SOME_TABLE st
GROUP BY st.value
But if you still want to use the INSERT/UPDATE approach:
IF EXISTS(SELECT NULL
FROM SOMETABLE WHERE ... > 1)
BEGIN
UPDATE TABLE
SET count = count + 1
WHERE value = #value
END
ELSE
BEGIN
INSERT INTO TABLE
(value, count)
VALUES
(#value, 1)
END
What about Update statement with inner join to perform +1, and Insert selected rows that do not exist in the first table.
Provide the tables schema and the columns you want to check and update so I can help.
Regards.
I want to check if there are any records in a table for a certain entry. I used COUNT(*) to check the number of records and got it to work. However, when the number of records for an entry is very high, my page loads slowly.
I guess COUNT(*) is causing the problem, but how do I check if the records exist without using it? I only want to check whether any records exist for the entry and then execute some code. Please help me find an alternative solution for this.
Thanks for any help.
There are several ways that may work. You can use exists, which lets the database optimise the method to get the answer:
if exists(select * from ...)
You can use top 1 so that the database can stop after finding the first match:
if (select count(*) from (select top 1 * from ...)) > 0
use select top 1 and check is there is an row
You can try selecting the first entry for given condition.
SELECT id FROM table WHERE <condition> LIMIT 1
I'm not sure if this will be quicker but you can try.
Other possible solution. How do you use count? COUNT(*)? If yes, then try using COUNT(id). As I remember this should be faster.
I would recommend testing to see if at least 1 record exists in the table, that meets your criteria then continue accordingly. For example:
IF EXISTS
(
SELECT TOP 1 Table_Name --Or Your ColumnName
FROM INFORMATION_SCHEMA.Tables -- Or your TableName
)
BEGIN
PRINT 'At least one record exists in table'
END
I found this on codeproject. It's quite handy.
-- Author,,Md. Marufuzzaman
SELECT SYS_OBJ.NAME AS "TABLE NAME"
, SYS_INDX.ROWCNT AS "ROW COUNT"
FROM SYSOBJECTS SYS_OBJ, SYSINDEXES SYS_INDX
WHERE SYS_INDX.ID = SYS_OBJ.ID
AND INDID IN(0,1) --This specifies 'user' databases only
AND XTYPE = 'U' --This omits the diagrams table of the database
--You may find other system tables will need to be ommitted,
AND SYS_OBJ.NAME <> 'SYSDIAGRAMS'
ORDER BY SYS_INDX.rowcnt DESC --I found it more useful to display
--The following line adds up all the rowcount results and places
--the final result into a separate column [below the first resulting table]
COMPUTE SUM(SYS_INDX.ROWCNT)
GO
you should use
select count(1) from
If you are saying (*) it will expand all the column's and then count