I have a SQL Server table with more than 15 columns.
One of my column name is verification_Status. Currently, I have 0, 1, 2, null values under verification_Status as below:
For example:
Id Name verification_Status
1 John 0
2 Kat 1
3 Williams Null
4 Rosy null
I want to make 0 wherever null appears. I have 4k rows to update so I am little worried.
update masterTable
set verification_Status = 0
where verification_Status == null
I am planning to use above query.
May I know this is the right query to my problem? Can someone guide me on this?
Use this:
update masterTable
set verification_Status = 0
where verification_Status is null
<> is Standard SQL; != is its T-SQL equivalent. Both evaluate for values, which NULL is not -- 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.
This is standard of all kinds of SQL management platforms
refer this: Null (SQL)
Your query should be
update masterTable set verification_Status=0 where verification_Status is null
Because NUll=NUll alwaysFalse. So the records which will have value as NULL in verification_status will not update zero. so you should use Verification_status is null at where clause.
Periodic update of value:
update masterTable set verification_Status=0 where verification_Status is null
Permanent Default Value on any table insert:
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
[WITH VALUES]
Check number of rows will affect before updating.
Select Count(*) from masterTable WHERE ISNULL(verification_Status,'') = ''
It is possible you also have empty string instead of null value in some columns.
If you want to update empty values and null values then use this.
UPDATE masterTable SET verification_Status=0 WHERE ISNULL(verification_Status,'') = ''
Related
I want to update a column of the table if the value is not null and if value is null then do not update that particular column and other columns should be updated in oracle update statement . Is there any simple way to achieve this in sql query ?
Looks like CASE expression might help.
update your_table set
that_column = case when that_column is not null then 'new value'
else null
end,
another_column = 123,
yet_another = 'ABC'
where ...
My sql query working fine but i have another issue some rows in my table have NULL values. i want to remove all NULL valued rows. Any recommendations?
Delete statement should work
DELETE FROM your_table
WHERE your_column IS NULL;
In case of multi column NULL check, I suggest using COALESCE
DELETE FROM your_table
WHERE COALESCE (your_column1, your_column2, your_column3 ) IS NULL;
If you want to delete a row where all columns values are null then use following query to delete:
DELETE FROM your_table
where your_column1 IS NULL
AND your_column2 IS NULL
AND your_column3 IS NUL;
But if you want to delete a row where any column value is null then use following query to delete:
DELETE FROM your_table
where your_column1 IS NULL
OR your_column2 IS NULL
OR your_column3 IS NUL;
You could start by filtering out columns you don't need, want, or will not use.
SELECT column1, column2, column3
FROM table
Then to remove the null values from your queries, use the IS NOT NULL command. Remember, null values can also be zeros, depending on how your tables and the data formats have been set up. In the example below, assume column2 is a number format.
WHERE column1 IS NOT NULL AND column2 > 0 AND column3 IS NOT NULL
I have a table PATIENT with Column STATUS. When I queried to get STATUS not equal to 1, I was expecting the result as NULL and 2.
But I am only getting 2 as the result. Can someone help me with this?
CREATE TABLE #PATIENT
(STATUS INT)
INSERT INTO #PATIENT (STATUS)
SELECT 1
UNION
SELECT 2
UNION
SELECT NULL
SELECT * FROM #PATIENT WHERE STATUS <> 1
When I queried with
SELECT * FROM #PATIENT WHERE ISNULL(STATUS, 0) != 1
I am able to get NULL and 2 as the result.
This is SQL SERVER 2012.
You can use OR in WHERE with Condition STATUS IS NULL .
SELECT * FROM #PATIENT WHERE STATUS <> 1 OR STATUS IS NULL
This will do it.
EDIT:
Conceptually, NULL means “a missing unknown value” and it is
treated somewhat differently from other values.
You cannot use arithmetic comparison operators such as =, <, or <>
to test for NULL
Because the result of any arithmetic comparison with NULL is also
NULL, you cannot obtain any meaningful results from such comparisons
we can not equate or not equate anything with null, thats why IS NULL
SELECT NULL <> 1 ===> NULL
Even though it is supposed to be true, it will return `NULL`
Hope this helps.
When you compare NULL value to any value then the result is always NULL.
So if you wan to select the NULL value as well then try this:
SELECT * FROM #PATIENT WHERE STATUS <> 1 OR STATUS IS NULL
DEMO
Conceptually "NULL" means a missing value. To test for NULL IS NULL or IS NOT NULL condition is used. Arithmetic operators cannot be used for comparing NULL values.
NULL<>1 :: returns false because NULL can be 1 or any other value (an unknown value).
Null is a special marker used in Structured Query Language (SQL) to indicate that a data value does not exist in the database.
And reason because you got only 2 and NOT NULL is because in SQL nothing is equal to NULL but also nothing is NOT equal to NULL.
In Simple words you cannot equate and not equate any value with NULL.
Let's say I want to display all items in a table with following criteria how would i do this?
SELECT *
FROM TABLE
WHERE TABLE.COLUMN1 = 'example' AND TABLE.COLUMN2 != 'NULL'
I want it to display all values from COLUMN1. How does one go about this process in MS SQL?
NULL values can be compared using IS [NOT] NULL in SQL server. Please check this.
SELECT *
FROM TABLE
WHERE TABLE.COLUMN1 = 'example' AND TABLE.COLUMN2 IS NOT NULL
NULL is an UNKNOWN value , you cannot use any Comparison Operators (= , <> , > , <) with it. you check for nulls like
ColumnName IS NULL or ColumnName IS NOT NULL
If you think about it , it makes sense, to compare two or more values, you need to know the values only then you can compare them, Since SQL Server considers a NULL to be an UNKNOWN value, you cannot really compare an unknown value to anything.
I have a table with a column called status of type smallint and accepts null. Sql server 2000.
My data contains mostly 2 in that field, but also 0 and null.
When I do
select *
from table
where status <> 2
I don't get all the proper records (where status is null or 0). Any idea why this is happening and how to correct? Shouldn't <> give me everything other than 2?
The NULL test doesn't match any arithmetic comparison.
use
where status <> 2 OR status is null
select *
from table
where ISNULL(status, 1) <> 2
NULL doesn't compare: so remove it.
Your example is the "common mistake" on Wikipedia too...
What you're expecting can be accomplished by setting ANSI_NULLS to off.
For example, try running these queries:
set ansi_nulls off
select case when 1 != null then 'true' else 'false' end
set ansi_nulls on
select case when 1 != null then 'true' else 'false' end
That being said, this is very non-standard SQL behaviour that you're expecting to see. NULL comparisons should always be considered false whether equals to or not equals to comparisons, as every developer will expect that type of SQL query behaviour.
Your WHERE clause should then look like:
where status <> 2 or status is null
Another option would be just to compare to status = 1, if that is the only status that you're expecting to be included in your query.