In oracle, it says to create a query that includes an employee column and a colleague column (works in the same department)
and I see part of the ff. query
WHERE e.employee_id <> c.employee_id
What does <> imply?
It means not equal to . It's the same as != in C-like languages.
<> (Not Equal To) Not equal to . also != is same
but <> is ISO Standard and
!= Not equal to (not ISO standard)
Related
In SQL where clause,
Is
.....
AND NOT (A OR B OR C)
.....
the same as
.....
AND ((NOT A) OR (NOT B) OR (NOT C))?
.....
Thank you!
No, it's not the same. First and second will return different result. First one will return the result of the or condition.
Query below will be like the first you wrote, it will filter and return result you want.
SELECT * FROM tablename
WHERE NOT(columnname= 'columnvalue' OR columnname= 'columnvalue')
For second one, you need to use AND instead of OR. This is because you apply 'NOT' to each one.
SELECT * FROM tablename
WHERE (NOT(columnname= 'columnvalue') AND NOT(columnname= 'columnvalue'))
You can refer to this example
SQL uses ternary logic with truth tables including true, false, and unknown to handle comparisons with null. In the OR truth table, (false or unknown) == unknown (which is falsy) but (true or unknown) == true
Consider:
SELECT 1
WHERE not (1=2 or 1=null)
Versus
SELECT 2
WHERE (not 1=2) or (1=null)
Example SqlFiddle
Redgate article with more about ternary logic in SQL
This question already has answers here:
Should I use != or <> for not equal in T-SQL?
(14 answers)
What is difference between operater != and <> in SQL Server? [duplicate]
(3 answers)
Closed 9 years ago.
What is difference between != and <> operators in Sql Server?
Since both are used as not operator. E.g :
select * from TableName where ColName <> value
or
select * from TableName where ColName != value
returns same values (Rows).
There is no difference. You can use both in MSSQL.
The MSSQL doc says:
!= functions the same as the <> (Not Equal To) comparison operator.
But <> is defined in the ANSI 99 SQL standard and != is not. So not all DB engines may support it and if you want to generate portable code I recommend using <>.
Most of the databases support both != and <> as not equal comparison operators. <> means either less than or greater than (i.e. not equal to) and was introduced because not all the keyboards used to have the exclamation ! key (a long time ago). Some databases like Oracle also support ^= for not equals.
I am confused and did not find in Google. Can anyone tell me What is Sql <> operator name?
<> is NOT Equal to, it's the same as !=
It's "not equal". Look in the list of operators for the database you're using, and find the appropriate section (usually "comparison operators"). For example:
SQL server
MySQL
Oracle
Postgres
It is the not equals operator.
Usage:
select *
from table
where foo <> 0
It is the Not Equal operator, but I am going to have to be verbose to get my answer posted because I haven't entered enough characters yet.
<> means not equal same as !=
Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. (a <> b) or (a != b) is true.
Here is the answer – Technically there is no difference between != and <>. Both of them work the same way and there is absolutely no difference in terms of performance or result.
If != and <> both are the same, which one should be used in SQL queries?
You can use either != or <> both in your queries as both technically same but I prefer to use <> as that is SQL-92 standard.
<>
What does this character mean when placed in an SQL query?
That's the SQL way of writing the not equal operator.
This means "not equal" operator in SQL query ieselect * from firstname <> 'james' this means give me all rows whose first name not equal to james
It's the SQL operator for "not equal", though many databases also provide the (non standard) != operator that means exactly the same.
this means 'Not Equal Operator.' ......!!!!!
Just as != in c and other languages. <> is for SQL
this operator means not equal ....
Not equal, i.e. Less than or greater than.
I just had a trivial but genuine use for NULLIF(), for the first time in my career in SQL. Is it a widely used tool I've just ignored, or a nearly-forgotten quirk of SQL? It's present in all major database implementations.
If anyone needs a refresher, NULLIF(A, B) returns the first value, unless it's equal to the second in which case it returns NULL. It is equivalent to this CASE statement:
CASE WHEN A <> B OR B IS NULL THEN A END
or, in C-style syntax:
A == B || A == null ? null : A
So far the only non-trivial example I've found is to exclude a specific value from an aggregate function:
SELECT COUNT(NULLIF(Comment, 'Downvoted'))
This has the limitation of only allowing one to skip a single value; a CASE, while more verbose, would let you use an expression.
For the record, the use I found was to suppress the value of a "most recent change" column if it was equal to the first change:
SELECT Record, FirstChange, NULLIF(LatestChange, FirstChange) AS LatestChange
This was useful only in that it reduced visual clutter for human consumers.
I rather think that
NULLIF(A, B)
is syntactic sugar for
CASE WHEN A = B THEN NULL ELSE A END
But you are correct: it is mere syntactic sugar to aid the human reader.
I often use it where I need to avoid the Division by Zero exception:
SELECT
COALESCE(Expression1 / NULLIF(Expression2, 0), 0) AS Result
FROM …
Three years later, I found a material use for NULLIF: using NULLIF(Field, '') translates empty strings into NULL, for equivalence with Oracle's peculiar idea about what "NULL" represents.
NULLIF is handy when you're working with legacy data that contains a mixture of null values and empty strings.
Example:
SELECT(COALESCE(NULLIF(firstColumn, ''), secondColumn) FROM table WHERE this = that
SUM and COUNT have the behavior of turning nulls into zeros. I could see NULLIF being handy when you want to undo that behavior. If fact this came up in a recent answer I provided. If I had remembered NULLIF I probably would have written the following
SELECT student,
NULLIF(coursecount,0) as courseCount
FROM (SELECT cs.student,
COUNT(os.course) coursecount
FROM #CURRENTSCHOOL cs
LEFT JOIN #OTHERSCHOOLS os
ON cs.student = os.student
AND cs.school <> os.school
GROUP BY cs.student) t