Are Brackets in The Where Clause Standard Sql

Are brackets in the WHERE clause standard sql

Yes. You can use parenthesis to bind components of where clauses. This isn't necessary in your example, but if you had multiple and and or components, you might need parenthesis to either ensure correct order of operations or simply to self-document the query.

Example 1:

select *
from foo
where 
   (class='A' and subclass='B')
   or (class='C' and subclass='D')

In example 1, the parens aren't strictly required because and binds more tightly than or, but if you had multiple or conditions tied by and you would need it to get correct results, as in example 2 below.

Example 2:

select *
from foo
where 
   (class='A' or class='B')
   and (subclass='C' or subclass='D')

I use them in either case, because I don't like having to parse the sql in my head the same way the query optimizer does -- I'd rather be explicit about it and more quickly understand what the intent is.

MySQL where and clauses in brackets

Yes, they are the same. The brackets here play the same role as all brackets do in conditionals.

When used with AND then they don't have any impact on the condition, as long as it only has AND within it. Same applies to statements that only has OR within. When used with both AND and OR then they do have an impact as long as they are used on sub-operations and not on the condition as a whole:

A AND (B OR C) != (A AND B) OR C

In SQL, brackets are also used for IN clause, EXISTS, sub-queries and other fundamentals

Parentheses Placement in Where Statements

if you wanted a variable @x to be not equal to 1 or 2, then you could write

@X <> 1 AND @X <> 2

but if you wrote

@X <> 1 OR @X <> 2

then it will be true for any number, so if @X was 1, then the second half is true, making the whole thing true

WHERE TRACK_GROUP = 'ED Tracking Group' AND  PT_ACUITY='3 - Two+ Resources' AND CHECKIN_DATE_TIME > @StartDate and CHECKIN_DATE_TIME < @EndDate 
    AND 
        (REASON_FOR_VISIT Not Like '%asthma%'   --it needs to be NOT like any of these, so all the conditions have to be true
     AND REASON_FOR_VISIT Not Like '%psych%')   --that is to say, each of the conditions is NOT like the value in quotes
     AND REASON_FOR_VISIT Not Like '%suicide%' 
     AND REASON_FOR_VISIT Not Like '%suicidal%'
     AND REASON_FOR_VISIT Not Like '%homicide%'
     AND REASON_FOR_VISIT Not Like '%homicidal%'
     AND REASON_FOR_VISIT Not Like '%FD-12%'
     AND REASON_FOR_VISIT Not Like '%behavioral%'
     AND REASON_FOR_VISIT Not Like '%overdose%'
     AND REASON_FOR_VISIT Not Like '%aggression%' )

What is the use of the square brackets [] in sql statements?

The brackets are required if you use keywords or special chars in the column names or identifiers. You could name a column [First Name] (with a space) – but then you'd need to use brackets every time you referred to that column.

The newer tools add them everywhere just in case or for consistency.

What does the SQL standard say about parentheses in SQL UNION/EXCEPT/INTERSECT statements?

There's no need for brackets/parenthesis in a UNION statement.

MySQL is the only one I'm aware of at this moment, which allows you to define ORDER BY and LIMIT clauses specific to each query as long as the query is enclosed in brackets -- standard SQL only allows a ORDER BY for the final result. The GROUP BY and HAVING clauses are specific to each query that makes up the UNION'd statement.

MySQL supports:

 (SELECT a.column
    FROM A_TABLE a
ORDER BY a.column DESC)
UNION
SELECT b.column
  FROM B_TABLE b

...which will cause no end of grief if you want/need to port to other databases.

Standard SQL only allows:

SELECT a.column
  FROM A_TABLE a
UNION
SELECT b.column
  FROM B_TABLE b
ORDER BY column DESC

[] brackets in sql statements

The [] marks the delimitation of a identifier, so if you have a column whose name contains spaces like Order Qty you need to enclose it with [] like:

select [Order qty] from [Client sales]

They are also to escape reserved keywords used as identifiers

How is where clause in SQL evaluated?

SELECT * FROM mytable
WHERE name='Anton' AND lastname='Gildebrand' OR age > 18 AND country='Sweden'

Is equal to:

SELECT * FROM mytable
WHERE (name='Anton' AND lastname='Gildebrand') OR (age > 18 AND country='Sweden')

Sources: TSQL, MySQL, Oracle, PostgreSQL

Meaning of square brackets [] in MS-SQL table designer?

The square brackets [] are used to delimit identifiers. This is necessary if the column name is a reserved keyword or contains special characters such as a space or hyphen.

Some users also like to use square brackets even when they are not necessary.

From MSDN:

Delimited identifiers

Are enclosed in double quotation marks (") or brackets ([ ]). Identifiers that comply with the rules for the format of identifiers may or may not be delimited.

SELECT *
FROM [TableX]         --Delimiter is optional.
WHERE [KeyCol] = 124  --Delimiter is optional.

Identifiers that do not comply with all of the rules for identifiers must be delimited in a Transact-SQL statement.

SELECT *
FROM [My Table]      --Identifier contains a space and uses a reserved keyword.
WHERE [order] = 10   --Identifier is a reserved keyword.

---

Related Topics