I'm working with a huge Access (.mdb) database, for my bad luck I can't change any table design, just able to create queries, well...
Having this table (part of):
Table1
Id Autonumber
Name Text(50) Not Null
Prod Text(8) Null
where Prod field is a date in format "ddMMyyyy", and not required.
With values like this:
Id Name Prod
------------------------
1 KX_W 06061988
2 AXR (null)
3 ELR 03021957
Then I'm trying this query, to get records according to a date:
PARAMETERS [#basedate] Date;
SELECT
Table1.Id,
Table1.Name
FROM
Table1
WHERE
((Table1.Prod) Is Not Null) AND
(GetDate(Table1.Prod) >= [#basedate])
ORDER BY
Table1.Id;
*GetDate() is a VBA module function that returns a Date value (dd/MM/yyyy) from a string argument.
When executing the query, I'm getting this message:
"This expression is typed incorrectly or it is too complex to be evaluated..."
The table is about 50K-record sized, but I'm pretty sure that's not the reason, there are other queries around this database, 10x more complex and run very quick!
I've tried with a piece of this table having no null values on Prod field and works fine, but when I try with the entire table, the message pop up; what is that I'm missing?
As a last resort, you can try to use a nested subquery.
SELECT SUB.ID, SUB.Name
FROM
(SELECT t.ID, t.Name, t.Prod WHERE t.Prod Is Not Null) AS SUB
WHERE GetDate(SUB.Prod) >= [#basedate]
ORDER BY SUB.ID
Related
I am currently working with a MS SQL database on Windows 2012 Server
I need to query only 1 column from a table that I only have access to read, not make any kind of changes.
Problem is that the name of the column is "Value"
My code is this:
SELECT 'Value' FROM table
If I add
`ORDER BY 'Value'`
The issue is that the query is returning an empty list of results.
Things I've tried already
I tried replacing ' with `"' but this didn't work either.
I also tried writing SELECT * instead of SELECT VALUE
Using the table name in the SELECT or ORDER clauses again didn't help
You are claiming that this query:
SELECT 'Value'
FROM table
ORDER BY 'Value'
Is returning no rows. That's not quite correct. It is returning an error because SQL Server does not allow constant expressions as keys for ORDER BY (or GROUP BY for that matter).
Do not use single quotes. In this case:
SELECT 'Value' as val
FROM table
ORDER BY val;
Or, if value is a column in the table:
SELECT t.Value
FROM table t
ORDER BY t.Value;
Value is not a reserved word in SQL Server, but if it were, you could escape it:
SELECT t.[Value]
FROM table t
ORDER BY t.[Value];
it looks like your table has null values. and because of the order by all null values come first.
try to add filter like this
select Value FROM table
where Value is not null and Value <> ''
order by Value
I am working on a query that will check the temp table if there is a record that do not exist on the main table. My query looks like this
SELECT * FROM [Telemarketing].[dbo].[PDCampaignBatch_temp]
WHERE [StartDateTime] NOT IN (SELECT [StartDateTime] FROM [Telemarketing].[dbo].PDCampaignBatch GROUP BY [StartDateTime])
but the problem is it does not display this row
even if that data does not exist in my main table. What seems to be the problem?
NOT IN has strange semantics. If any values in the subquery are NULL, then the query returns no rows at all. For this reason, I strongly recommend using NOT EXISTS instead:
SELECT t.*
FROM [Telemarketing].[dbo].[PDCampaignBatch_temp] t
WHERE NOT EXISTS (SELECT 1
FROM [Telemarketing].[dbo].PDCampaignBatch cb
WHERE t.StartDateTime = cb.StartDateTime
);
If the set is evaluated by the SQL NOT IN condition contains any values that are null, then the outer query here will return an empty set, even if there are many [StartDateTime]s that match [StartDateTime]s in the PDCampaignBatch table.
To avoid such issue,
SELECT *
FROM [Telemarketing].[dbo].[PDCampaignBatch_temp]
WHERE [StartDateTime] NOT IN (
SELECT DISTINCT [StartDateTime]
FROM [Telemarketing].[dbo].PDCampaignBatch
WHERE [StartDateTime] IS NOT NULL
);
Let's say PDCampaignBatch_temp and PDCampaignBatch happen to have the same structure (same columns in the same order) and you're tasked with getting the set of all rows in PDCampaignBatch_temp that aren't in PDCampaignBatch. The most effective way to do that is to make use of the EXCEPT operator, which will deal with NULL in the expected way as well:
SELECT * FROM [Telemarketing].[dbo].[PDCampaignBatch_temp]
EXCEPT
SELECT * FROM [Telemarketing].[dbo].[PDCampaignBatch]
In production code that is not a one-off, don't use SELECT *, write out the column names instead.
Most likely your issue is with the datetime. You may be only displaying a certain degree of percision like the year/month/date. The data may be stored as year/month/date/hour/minute/second/milisecond. If so you have to match down the the most granluar measurement of the data. If one field is a date and the other is a date time they also will likely never match up. Thus you always get no responses.
I get the following error message
"Your query does not include the specified expression 'SampleCode' as part of an aggregate function."
I've looked into aggregate functions and have tried various ways to GROUP BY using the individual data fields that make up the code but I can't seem to get anything to work.
'SampleCode' is a concatenated query field (query name: datqry_SampleNumber) that is based on data from 3 different tables to create a unique value as follows...
SampleCode: IIf([tbl_Carcass.SampleNumber]="-999","-999",
"NPT-" & [tbl_SurveyInfo.SurveyYear*] & "-" &
[datqry_TransectData.Project_Code] & "-" & [tbl_Carcass.SampleNumber])
for SampleNumber values > 0001 (-999 is a placeholder indicating no SampleNumber assigned). Note, SurveyYear* is a calculated field based on the SurveyDate data field.
So, since SampleCode needs to be unique to each sample, I am trying to build a duplicate query, based on the aforementioned query, to identify duplicate SampleCodes so they can be relabeled and archived w/ a unique qualifier. The criteria for the duplicate query operation is as follows
In (SELECT [SampleCode] FROM [datqry_SampleNumber] As Tmp
GROUP BY [SampleCode] HAVING Count(*)>1 )
Any ideas on how to tackle this problem? Thank you in advance for your help and suggestions.
This looks like it might be a limitation of the JET engine used by Access to interpret its SQL.
It appears to be having trouble working with the subquery because it contains an aggregation of a calculated field (SampleCode in your case).
Try saving this as a separate query called, e.g. qryDuplicates:
SELECT [SampleCode] FROM [datqry_SampleNumber]
GROUP BY [SampleCode] HAVING Count(*)>1;
Then what you are trying to do will work as expected:
SELECT * from someTable WHERE someField IN (
SELECT * FROM qryDuplicates
);
TECHNICAL NOTE: I've tested it out and it is indeed specific to the fact that SampleCode is a calculated field. Doing exactly the same kind of grouped subquery works as expected when the field in question is not calculated.
With this test database this query works:
SELECT * FROM Table2 WHERE Field3 IN (
SELECT Field1 FROM datqry_SampleNumber
GROUP BY Field1 HAVING COUNT(*) > 1
);
And this doesn't
SELECT * FROM Table2 WHERE Field3 IN (
SELECT SampleCode FROM datqry_SampleNumber
GROUP BY SampleCode HAVING COUNT(*) > 1
);
I have a simple SQL query where a comparison is done between two tables for mismatching value.
Yesterday, we picked up an issue where one field was null and the other wasn't, but a mismatch was not detected.
As far as I can determine,the logic has been working all along until yesterday.
Here is the logic of the SQL:
CREATE TABLE Table1
(UserID INT,PlayDate DATETIME)
CREATE TABLE Table2
(UserID INT,PlayDate DATETIME)
INSERT INTO Table1 (UserID)
SELECT 5346
INSERT INTO Table2 (UserID,PlayDate)
SELECT 5346,'2012-11-01'
SELECT a.UserID
FROM Table1 a
INNER JOIN
Table2 b
ON a.UserID = b.UserID
WHERE a.PlayDate <> b.PlayDate
No values are returned even though the PlayDate values are different.
I have now updated the WHERE to read:
WHERE ISNULL(a.PlayDate,'') <> ISNULL(b.PlayDate,'')
Is there a setting in SQL which someone could have changed to cause the original code to no longer pick up the difference in fields?
Thanks
NULL <> anything
is unknown not true. SQL uses three valued logic (false/true/unknown) and the predicate needs to evaluate to true in a where clause for the row to be returned.
In fact in standard SQL any comparison with NULL except for IS [NOT] NULL yields unknown. Including WHERE NULL = NULL
You don't state RDBMS but if it supports IS DISTINCT FROM you could use that or if you are using MySQL it has a null safe equality operator <=> you could negate.
You say you think it previously behaved differently. If you are on SQL Server you might be using a different setting for ANSI_NULLS somehow but this setting is deprecated and you should rewrite any code that depends on it anyway.
You can simulate IS DISTINCT FROM in SQL Server with WHERE EXISTS (SELECT a.PlayDate EXCEPT SELECT b.PlayDate)
Not even a NULL can be equal to NULL.
Here are two common queries that just don’t work:
select * from table where column = null;
select * from table where column <> null;
there is no concept of equality or inequality, greater than or less
than with NULLs. Instead, one can only say “is” or “is not”
(without the word “equal”) when discussing NULLs.
- The correct way to write the queries
select * from table where column IS NULL;
select * from table where column IS NOT NULL;
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.