Difference Between <> and != in Sql

What is difference between != and in sql server

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 <>.

difference between and !=

For SQL Server:

They are the same. Both are two Not Equal To operators. But != is not ISO standard, as quoted from Comparison Operators:

<> (Not Equal To) Not equal to

!= (Not Equal To) Not equal to (not ISO standard)

Difference between and != in SQL

None whatsoever, syntactically.

Both are inequality operators, <> is the SQL-92 standard, however its interchangable on some platforms with != (E.g. SQL Server)

Difference between and != operators in MSSQL Server

!= is not ANSI compliant.

That's all.

Use <>

UPD. Oh, here

What is the difference between NOT and != operators in SQL?

NOT negates the following condition so it can be used with various operators. != is the non-standard alternative for the <> operator which means "not equal".

e.g.

NOT (a LIKE 'foo%')
NOT ( (a,b) OVERLAPS (x,y) )
NOT (a BETWEEN x AND y)
NOT (a IS NULL)

Except for the overlaps operator above could also be written as:

a NOT LIKE 'foo%'
a NOT BETWEEN x AND y
a IS NOT NULL

In some situations it might be easier to understand to negate a complete expression rather then rewriting it to mean the opposite.

NOT can however be used with <> - but that wouldn't make much sense though: NOT (a <> b) is the same as a = b. Similarly you could use NOT to negate the equality operator NOT (a = b) is the same as a <> b

What is the difference between and != operators in MySQL?

They are both exactly the same. See the documentation.

http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#operator_not-equal

Difference between = and is in sql server

Nothing equals null.

Not even null equals null.

null is not a value, it is more like a concept, or a mark, meaning unknown value.

As such, you need two operators for this, one for equality, and one for checking the concept of null.

Once you start to think of null as "unknown value" a lot of the other behavior also makes sense.

10 + null? Add an unknown value to 10? Obviously you will have another unknown value as a result.

For more information, please check the documentation of the equality operator in T-SQL.

Additionally, see the documentation for SET ANSI_NULL.

Note that the documentation is in conflict about the behavior of x = null between the equality operator (documentation says it will always be false if x is non-null) whereas SET ANSI_NULLS documentation says that x = null will behave equivalent to x is null when the option is turned on.

Should I use != or for not equal in T-SQL?

Technically they function the same if you’re using SQL Server AKA T-SQL. If you're using it in stored procedures there is no performance reason to use one over the other. It then comes down to personal preference. I prefer to use <> as it is ANSI compliant.

You can find links to the various ANSI standards at...

http://en.wikipedia.org/wiki/SQL

Performance differences between equal (=) and IN with one literal value

There is no difference between those two statements, and the optimiser will transform the IN to the = when IN has just one element in it.

Though when you have a question like this, just run both statements, run their execution plan and see the differences. Here - you won't find any.

After a big search online, I found a document on SQL to support this (I assume it applies to all DBMS):

If there is only one value inside the parenthesis, this commend [sic] is equivalent to,
WHERE "column_name" = 'value1

Here is the execution plan of both queries in Oracle (most DBMS will process this the same):

EXPLAIN PLAN FOR
select * from dim_employees t
where t.identity_number = '123456789'

Plan hash value: 2312174735
-----------------------------------------------------
| Id  | Operation                   | Name          |
-----------------------------------------------------
|   0 | SELECT STATEMENT            |               |
|   1 |  TABLE ACCESS BY INDEX ROWID| DIM_EMPLOYEES |
|   2 |   INDEX UNIQUE SCAN         | SYS_C0029838  |
-----------------------------------------------------

And for IN() :

EXPLAIN PLAN FOR
select * from dim_employees t
where t.identity_number in('123456789');

Plan hash value: 2312174735
-----------------------------------------------------
| Id  | Operation                   | Name          |
-----------------------------------------------------
|   0 | SELECT STATEMENT            |               |
|   1 |  TABLE ACCESS BY INDEX ROWID| DIM_EMPLOYEES |
|   2 |   INDEX UNIQUE SCAN         | SYS_C0029838  |
-----------------------------------------------------

As you can see, both are identical. This is on an indexed column. Same goes for an unindexed column (just full table scan).

What's the difference between LIKE and = in SQL?

As per SQL standard, the difference is treatment of trailing whitespace in CHAR columns. Example:

create table t1 ( c10 char(10) );
insert into t1 values ('davyjones');

select * from t1 where c10 = 'davyjones';
-- yields 1 row

select * from t1 where c10 like 'davyjones';
-- yields 0 rows

Of course, assuming you run this on a standard-compliant DBMS. BTW, this is one the main differences between CHARs and VARCHARs.