I have a Users table like this -
Table View
I am using the following query to retrieve rows where Faculty ID is CSE001, Designation is not student and User Role is not Marketing Coordinator -
Query view
But it's not giving me the result I need, cause the 2 rows I was expecting to have in return, has null in their UserRole column. So, it returns nothing.
Query Result
So, how can I write the query, so that it returns me the rows even if they have null in UserRole column? Can anyone help me, please? Thanks...
Check for both Designation and UserRole if they contain NULL values.
Use IS NULL or IS NOT NULL for these kind of checks. This is because you cannot compare NULL with specific values.
SELECT * FROM Users
WHERE FacultyId = 'CSE001'
AND (Designation <> 'Student' OR Designation IS NULL)
AND (UserRole <> 'Marketing Coordinator' OR UserRole IS NULL)
Hope this helps.
In SQL Server, values can be missing but applicable, such as the value of a hair's color that has not been supplied for a person, or can be missing but inapplicable, such as the value for a bold person. In either case, SQL Server will mark missing values as NULL. A NULL is neither TRUE, nor FALSE, but UNKNOWN. This is the third value in three-valued logic. In other words, you can determine whether X = Y is TRUE or FALSE when you know the values of both X and Y, but what if X is missing? SQL Server will return UNKNOWN, marked as NULL. This is your case: you know that Y is known (equals 'Marketing Coordinator'), but X might be missing. Because WHERE returns only those rows which match the conditions (i.e. each predicate is evaluated as TRUE), UNKNOWN results will be filtered out.
You will need to write queries that use three-valued logic to account for three possible outcomes: TRUE, FALSE and UNKNOWN. In ON, WHERE and the HEAVING clauses, SQL Server will treat NULL as FALSE. On the other hand, ORDER BY sorts the NULLs together and first.
You can test for NULL values with IS NULL or IS NOT NULL operators rather than equal.
You have explicitly ask for NULL values because they're quite special in relational databases.
This would be right one:
SELECT *
FROM Users
WHERE FacultyId <>'CSE001'
AND Designation <> 'Student'
AND (UserRole <> 'Marketing Coordinator' OR UserRole IS NULL);
Related
I need to merge some randomly uppercased data that has been collected in an SQLite table key_val, such that key is always lowercase and no vals are lost. There is a unique compound index on key,val.
The initial data looks like this:
key|val
abc|1
abc|5
aBc|1
aBc|5
aBc|3
aBc|2
AbC|1
abC|3
The result after the merge would be
key|val
abc|1
abc|2
abc|3
abc|5
In my programmer brain, I would
for each `key` with upper case letters;
if a lower cased `key` is found with the same value
then delete `key`
else update `key` to lower case
Re implementing the loop has a sub query for each row found with upper case letters, to check if the val already exists as a lower case key
If it does, I can delete the cased key.
From there I can UPDATE key = lower(key) as the "duplicates" have been removed.
The first cut of the programming method of finding the dupes is:
SELECT * FROM key_val as parent
WHERE parent.key != lower(parent.key)
AND 0 < (
SELECT count(s.val) FROM key_val as s
WHERE s.key = lower(parent.key) AND s.val = parent.val
)
ORDER BY parent.key DESC;
I'm assuming there's a better way to do this in SQLite? The ON CONFLICT functionality seems to me like it should be able to handle the dupe deletion on UPDATE but I'm not seeing it.
First delete all the duplicates:
DELETE FROM key_val AS k1
WHERE EXISTS (
SELECT 1
FROM key_val AS k2
WHERE LOWER(k2.key) = LOWER(k1.key) AND k2.val = k1.val AND k2.rowid < k1.rowid
);
by keeping only 1 combination of key and val with the min rowid.
It is not important if you kept the key with all lower chars or not, because the 2nd step is to update the table:
UPDATE key_val
SET key = LOWER(key);
See the demo.
Honestly it might just be easier to create a new table and then insert into it. As it seems you really just want a distinct select here, use:
INSERT INTO kev_val_new ("key", val)
SELECT DISTINCT LOWER("key"), val
FROM key_val;
Once you have populated the new table, you may drop the old one, and then rename the new one to the previous name:
DROP TABLE key_val;
ALTER TABLE key_val_new RENAME TO key_val;
I agree with #Tim that it would be easire to re-create table using simple select distict lower().. statement, but that's not always easy if table has dependant objects (indexes, triggers, views). In this case this can be done as sequence of two steps:
insert lowered keys which are not still there:
insert into t
select distinct lower(tr.key) as key, tr.val
from t as tr
left join t as ts on ts.key = lower(tr.key) and ts.val = tr.val
where ts.key is null;
now when we have all lowered keys - remove other keys:
delete from t where key <> lower(key);
See fiddle: http://sqlfiddle.com/#!5/84db50/11
However this method assumes that key is always populated (otherwise it would be a strange key)
If vals can be null then "ts.val = tr.val" should be replaced with more complex stuff like ifnull(ts.val, -1) = ifnull(tr.val, -1) where -1 is some unused value (can be different). If we can't assume any unused value like -1 then it should be more complex check for null / not null cases.
I’m attempting to count records that match specific criteria, including one field being null, but including the null clause results in no records being found.
If I output the contents of the field, it comes back as “(null)”. I’ve tried IS NULL and ISNULL, both of which appear that they should work when looking at other sources, but they both fail for me.
SELECT calls.contact_number, calls.contact_name, COUNT(notes.id) AS note_count
FROM calls LEFT JOIN notes on calls.id = notes.call_id
WHERE calls.contact_number = "123" AND notes.group_id ISNULL
GROUP BY calls.contact_number
This returns no records, whereas I’m expecting it to return one.
Move the condition in the ON clause:
SELECT calls.contact_number, calls.contact_name, COUNT(notes.id) AS note_count
FROM calls LEFT JOIN notes
ON calls.id = notes.call_id AND notes.group_id IS NULL
WHERE calls.contact_number = "123"
GROUP BY calls.contact_number, calls.contact_name
After grabbing a copy of the database, the notes.group_id field was determined to be an integer type, and the record in question actually contained a 0.
The successful query ended up being
SELECT calls.contact_number, calls.contact_name, COUNT(notes.id) as note_count
FROM calls LEFT JOIN notes
ON calls.id = notes.call_id
WHERE calls.contact_number = “123” AND (notes.group_id IS NULL OR notes.group_id = 0)
GROUP BY calls.contact_number
Not sure why the NSLog output of the returned value for group_id was ‘(null)’, some weird conversion?
In the select statement i need to return a value based on the data on other two colomns. For example,
select clarify, clarify_rece_date, clarify_process_date
from test_db;
So the clarify should return yes if both clarify_rece_date and clarify_process_date is not null and if they null clarify should return No.
I could have use decode here if i want to check only onle column as below,
select decode(clarify_rece_date, null,'Yes','No') clarify, clarify_rece_date, clarify_process_date
from test_db;
But how can i check for both columns in this scenario?
You could have a rather complex DECODE. However, it would make far more sense to use a CASE statement
SELECT (CASE WHEN clarify_rece_date IS NOT NULL AND
clarify_process_date IS NOT NULL
THEN 'Yes'
ELSE 'No'
END) clarify,
clarify_rece_date,
clarify_process_date
FROM test_db
I have a table named CUSTOMER, with few columns. One of them is Customer_ID.
Initially Customer_ID column WILL NOT accept NULL values.
I've made some changes from code level, so that Customer_ID column will accept NULL values by default.
Now my requirement is that, I need to again make this column to accept NULL values.
For this I've added executing the below query:
ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL
I'm getting the following error:
ORA-01451 error, the column already allows null entries so
therefore cannot be modified
This is because already I've made the Customer_ID column to accept NULL values.
Is there a way to check if the column will accept NULL values before executing the above query...??
You can use the column NULLABLE in USER_TAB_COLUMNS. This tells you whether the column allows nulls using a binary Y/N flag.
If you wanted to put this in a script you could do something like:
declare
l_null user_tab_columns.nullable%type;
begin
select nullable into l_null
from user_tab_columns
where table_name = 'CUSTOMER'
and column_name = 'CUSTOMER_ID';
if l_null = 'N' then
execute immediate 'ALTER TABLE Customer
MODIFY (Customer_ID nvarchar2(20) NULL)';
end if;
end;
It's best not to use dynamic SQL in order to alter tables. Do it manually and be sure to double check everything first.
Or you can just ignore the error:
declare
already_null exception;
pragma exception_init (already_null , -01451);
begin
execute immediate 'alter table <TABLE> modify(<COLUMN> null)';
exception when already_null then null;
end;
/
You might encounter this error when you have previously provided a DEFAULT ON NULL value for the NOT NULL column.
If this is the case, to make the column nullable, you must also reset its default value to NULL when you modify its nullability constraint.
eg:
DEFINE table_name = your_table_name_here
DEFINE column_name = your_column_name_here;
ALTER TABLE &table_name
MODIFY (
&column_name
DEFAULT NULL
NULL
);
I did something like this, it worked fine.
Try to execute query, if any error occurs, catch SQLException.
try {
stmt.execute("ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL");
} catch (SQLException sqe) {
Logger("Column to be modified to NULL is already NULL : " + sqe);
}
Is this correct way of doing?
To modify the constraints of an existing table
for example... add not null constraint to a column.
Then follow the given steps:
1) Select the table in which you want to modify changes.
2) Click on Actions.. ---> select column ----> add.
3) Now give the column name, datatype, size, etc. and click ok.
4) You will see that the column is added to the table.
5) Now click on Edit button lying on the left side of Actions button.
6) Then you will get various table modifying options.
7) Select the column from the list.
8) Select the particular column in which you want to give not null.
9) Select Cannot be null from column properties.
10) That's it.
It seems like a dumb question, and yet. It could be my IDE that's goofing me up. Here's the code (this is generated from DbLinq):
SELECT pics$.Caption, pics$.Id, pics$.Path, pics$.Public, pics$.Active, portpics$.PortfolioID
FROM main.Pictures pics$
inner join main.PortfolioPictures portpics$ on pics$.Id = portpics$.PictureId
WHERE portpics$.PortfolioId = 1 AND pics$.Id > 0
--AND pics$.Active = 1 AND pics$.Public = 1
ORDER BY pics$.Id
If I run this query I get three rows back, with two boolean fields called Active and Public. Adding in the commented out line returns no rows. Changing the line to any of the following:
pics$.Active = 'TRUE'
pics$.Active = 't'
pics$.Active = boolean(1)
It doesn't work. Either errors or no results. I've googled for this and found a dearth of actual SQL queries out there. And here we are.
So: how do I use a boolean field in a where clause in SQLite?
IDE is SQLite Administrator.
Update: Well, I found the answer. SQLite Administrator will let you make up your own types apparently; the create SQL that gets generated looks like this:
CREATE TABLE [Pictures] ([Id] INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
[Path] VARCHAR(50) UNIQUE NOT NULL,[Caption] varchAR(50) NULL,
[Public] BOOLEAN DEFAULT '0' NOT NULL,[Active] BOOLEAN DEFAULT '1' NOT NULL)
The fix for the query is
AND pics$.Active = 'Y' AND pics$.Public = 'Y'
The real issue here is, as the first answerer pointed out, there is no boolean type in SQLite. Not an issue, but something to be aware of. I'm using DbLinq to generate my data layer; maybe it shouldn't allow mapping of types that SQLite doesn't support. Or it should map all types that aren't native to SQLite to a string type.
You don't need to use any comparison operator in order to compare a boolean value in your where clause.
If your 'boolean' column is named is_selectable, your where clause would simply be:
WHERE is_selectable
SQLite does not have the boolean type: What datatypes does SQLite support?
The commented-out line as it is should work, just use integer values of 1 and 0 in your data to represent a boolean.
SQLite has no built-in boolean type - you have to use an integer instead. Also, when you're comparing the value to 'TRUE' and 't', you're comparing it to those values as strings, not as booleans or integers, and therefore the comparison will always fail.
Source: http://www.sqlite.org/datatype3.html
--> This Will Give You Result having False Value of is_online field
select * from device_master where is_online!=1
--> This Will Give You Result having True Value of is_online field
select * from device_master where is_online=1