I have a query which has this statement in the where clause:
AND (s1_.sync_id IS NULL OR s1_.sync_id = 0)
In the database I have this value:
sync_id
NULL --> NULL
invalid --> String 'invalid'
The query does select the row with the string "invalid" as well. I do not see why, because it is neither NULL nor 0.
I do want to select the rows with NULL or 0, but I do not want to select the row with a value which is different from these two.
Does anybody know what is happening here?
Thanks.
A small update required in your query:
AND (s1_.sync_id IS NULL OR s1_.sync_id = '0')
You need to cover 0 with '' as sync_id stores strings not the Integers.
Related
Hope the question is not too generic. Couldn't find anything on the site or in SQL documentation:
While coding, i tested this, and to my surprise it worked:
SELECT * FROM cal_entry WHERE cal_entry.parent_id <> 'null'
It actually shows the rows without the ones with NULL values (these are real NULL values in database, not strings with 'null' inside).
According to the docs, I should have used NOT NULL, of course. By the way, it doesn't work with = 'null', like it is correctly stated in the docs.
Can someone explain that?
You are selecting all rows where <> 'null' is true.
Comparing(equals or not-equals) to null is null, so if a row where cal_entry.parent_id is null, your condition will be false/null.
So your query gets all rows that are not null, nor contain the string 'null'.
(Note, you could just as well have written <>'something_else')
Assuming parent_id in an int column the query will return all non-null, non-zero rows:
SELECT *
FROM (
SELECT NULL AS parent_id UNION ALL
SELECT 0 UNION ALL
SELECT 1 UNION ALL
SELECT 2
) AS cal_entry
WHERE cal_entry.parent_id <> 'null'
-- returns 1 and 2 but not 0!
When comparing a number to string MySQL will convert the string to number. Some examples:
'null' becomes 0
'asdf' becomes 0
'1asdf' becomes 123
'1' becomes 1
Your query will behave like:
WHERE cal_entry.parent_id <> 0
this operator give you result of not equal to. ex. $var != null.
we write in mysql as <>. this is kind of validation that the value shoud never be equal to null.
When working with null following two statements should always be taken note of -
An expression can be null, but it can never be equal to null.
Two nulls are never equal to each other.
So, in your query wherever there is a comparison null<>null it returns true by second statement.
Also, always account the possibility that some rows might contain null -
Select * from cal_entry where cal_entry.parent_id!=10
This query would leave out the rows with null entries. Instead use -
Select * from cal_entry where cal_entry.parent_id!=10 or cal_entry.parent_id is null
I'm having a problem with some SQL queries that I cant figure out.
SELECT * FROM MasterList WHERE Requested <> "Yes";
If I run the above query on my table I get 60 records returned. However There should be close to 300. I think the issue is, some of the records are just blank in the Requested field and others are NULL. But I would have thought NULL would still count as not equal to "Yes" wouldnt it? If not, is there a way around that without having to go back and 'blank' all the null fields?
Nulls are not counted in comparison, if you want null values to be returned then you need to execute the following query:
SELECT * FROM MasterList WHERE Requested <> "Yes" OR Requested IS NULL;
<=>
NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.
mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1, 1, 0
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
-> 1, NULL, NULL
in your case use:
SELECT * FROM MasterList WHERE not Requested <=> "Yes"
It happens because null <> 'Yes' expression evaluates to null, thus you should add a separate is null check to include records that meet this condition in your result set:
select * from MasterList where Requested <> "Yes" or Requested is null
P.S.: comparison of null with anything, even with null itself, always returns null.
I've struggled with the same issue and someone introduced me to the IS DISTINCT FROM construct. Very useful but not available for all DBMS!
SELECT * FROM MasterList WHERE Requested IS DISTINCT FROM "Yes";
I have a table named 'datatablecoulmn' with the following columns.
now i want all rows where the column FkID is NULL.FkID is an integer field
i tried the following queries
SELECT * FROM `datatablecoulmn` WHERE `FkID`=NULL
SELECT * FROM `datatablecoulmn` WHERE `FkID`<1
SELECT * FROM `datatablecoulmn` WHERE `FkID`='null'
All of these returns empty rows .Any help?
In MySQL, NULL is considered as a 'missing, unknown value', as opposed to no value. Any arithmetic comparison with NULL does not return true or false, but returns NULL instead., So, NULL != 'C' returns NULL, as opposed to returning true.
Use IS NULL condition in your query and try like this
SELECT * FROM `datatablecoulmn` WHERE `FkID` IS NULL
For handling NULL values MySQL provides three operators
IS NULL: operator returns true if column value is NULL.
IS NOT NULL: operator returns true if column value is not NULL.
<=>: operator compares values, which (unlike the = operator) is true
even for two NULL values.
You can refer to these links for more
Link 1,Link 2,Link 3
You can't compare with NULL. So you gotta check for YourColumn IS NULL (or maybe YourColumn IS NOT NULL.
NULL is a value like infinity is a number. In other words, not at all. NULL is the absence of certain information.
For the same reason that NaN (not a number) in IEEE754 floating point is not equal to other instances (or even the same instance) of NaN, nothing in SQL is equal to NULL, including NULL.
That's something that may sound strange but, when you think of the purpose of NULL, that of specifying unknown or inappropriate values, it makes sense.
In order to see if a value is NULL, you have to therefore use something like:
where COLUMN_NAME is null
More details on working with NULL in MySQL can be found here.
Use something like:
SELECT * FROM `datatablecoulmn` WHERE `FkID` is NULL
NULL is a placeholder to say there is the absence of a value. Which is why you can only use IS NULL/IS NOT NULL as predicates for such situations and not = or != or <> which is used by values.
Here is another way to exclude the records with FkID is NOT NULL:
SELECT D1.*
FROM datatablecoulmn D1
WHERE NOT EXISTS (SELECT D2.*
FROM datatablecoulmn D2
WHERE D2.`FkID` IS NOT NULL)
In mysql table real_account_id's data type is int(11).
I want to fetch all records with NULL values.
I am using this simple query.
SELECT * FROM `customer_payment_options` WHERE real_account_id = NULL
But, it's not giving me any results. There are 2 records in database with NULL value.
I also tried with,
SELECT * FROM `customer_payment_options` WHERE real_account_id = 'NULL'
Why is it like this?
Thanks.
NULL is equal to nothing including NULL. That's why you must use IS NULL:
SELECT * FROM `customer_payment_options` WHERE real_account_id IS NULL
I can't seem to find an answer to my question probably because I cannot formulate it correctly so asking here is my last option. I need to select a row which has a certain column any value that does not evaluate to false. Let me give some examples because I am having a hard time explaining this..
SELECT * FROM table WHERE bool(column)!=false
should match every row where the value of col is not
'0' (string)
'' (string)
0 (integer)
NULL
This seems trivial but i may have not understand your question
SELECT * FROM table WHERE column <> '0' and column <> '' and column <> 0 and column is not null
Now please tell me why you end up with such a mess. A column can either be integer or text, never both. SQL is not PHP!