What is the purpose of this symbol in MySQL queries?
`
For example:
SELECT `show` FROM table WHERE id = "4"
In MySQL the backtick is used to quote column names. It is normally optional but here it is needed because SHOW is a reserved word.
A list of reserved words can be found here.
There is a difference between quotation marks (' and ") and backticks (`) in mysql.
Backticks are known as an "identifier quote" and are used to surround identifiers, such as:
tables
columns
indexes
stored functions
etc.
Quote go around strings, often used when inserting, updating, or trying to match against a string in the database (eg a WHERE clause)
Backticks are known as an "identifier quote" and are used to surround identifiers, such as: you can live without them but but they are necessary when
identifiers name contains spaces e.g. a column name is `customer name `
identifiers name is a reserved work e.g. a column name is `name `
Related
Is it possible to escape a SQL identifier in either MySQL or BigQuery or any other RDBMS that allows quoting of identifiers with the ` character? For example:
select 1 as `select`
Works, but then How would I add a literal backtick to it, or is that just not allowed?
select 1 as `sel\`ect`
Yes. Use a doubled backtick, eg:
create table `my``table` (`my``id` int);
This is similar syntax for including quotes in text, eg 'O''Leary'
See live demo of
create table `my``table` (`my``id` int);
insert into `my``table` (`my``id`) values (1);
select * from `my``table`;
outputs:
my`id
1
By the way, the documentation says any UTF-8 character (except U+0000) is allowed in a back tick quoted identifier.
I'm new to SQL and recently I've had problems working with my table that contains a column name of 'S#'.
So what I currently have is
SELECT S#, SNAME FROM S WHERE CITY = 'London';
but the S# part gives me an operator error. I've tried casting it as a varchar and doing [S#] but nothing works. Any help would be appreciated.
Thanks
Use backticks or double quotes to escape the name:
SELECT `S#`, SNAME
FROM S
WHERE CITY = 'London';
When you design your own databases, don't use such characters in names. Stick to letters, numbers, and underscore.
Using Backticks, Double Quotes, and Single Quotes in any MySQL database can be summarized into two points:
Quotes (Single and Double) are used around strings.
Backticks are used around table and column identifiers.
Using backticks in your query,
SELECT `S#`, SNAME
FROM S
WHERE CITY = 'London';
These backticks are called quoted identifiers and they tell the parser to handle the text between them as a literal string. They are useful for when you have a column or table that contains a keyword or space or some special character.
In my case, the backticks around that column name work but double quotes don't.
The last person in my job has flooded column names with special characters such as (?,!, and /), as well as used many reserved keywords for column names (more often than not, timestamp or user is used).
Normally, I step around this by using double quotes or brackets to escape the SQL object. A subset of the full list of columns are below:
DriverID,
Department,
Odometer,
MerchantState,
MerchantCity,
gallons/Units,
timestamp,
tax
Inside my query, I wrap the two columns in question (gallons/units and timestamp) inside double quotes. Timestamp because it's a reserved keyword, and Gallons/units, because without the quotes, SQL reads the query, stops at the slash, and tells me "Gallons" is not a column inside the table.
If I do wrap double quotes around the column name, SQL returns a different error: "Operand should contain 1 column(s)".
I've tried every variant (only capturing the slash in quotes, quoting both, using brackets, mixing brackets and quotes, etc. but with to no avail).
Is there anything I can do to fix this query short of renaming the column name and changing the associated code in the program that pulls from it? (the really tedious task I'm trying to avoid).
In SQL Server, identifiers can be delimited using square brackets, e.g.
SELECT [gallons/units] ...
In MySQL, identifiers can be delimited using backticks, e.g.
SELECT `gallons/units` ...
(NOTE: If MySQL SQL_MODE includes ANSI_QUOTES, then double quotes are treated as delimiters for identifiers, similar to the way Oracle handles double quotes; absent that setting, double quotes are handled as delimiters for string literals. With ANSI_QUOTES included SQL_MODE, "gallons/units" will be interpreted as an identifier (column name). Without ANSI_QUOTES, MySQL will see it as a string literal, as if it were enclosed in single quotes.)
FOLLOWUP:
As far as an error "operand should contain only 1 column(s)", that's usually a problem with query semantics, not an issue with escaping identifiers.
A subquery in the SELECT list can return only a single expression, for example, this would throw an error:
Query: SELECT 'foo' , ( SELECT 'fee' AS fee, 'fi' AS fi )
Error Code: 1241
Operand should contain 1 column(s)
You can try backticks instead of double quotes
`gallons/units`
There are a couple of options. First, have you tried using %/ to escape the slash?
Example: "select * from 'gallons%/units';"
Second one I've found, which may or may not be helpful, is to provide an escape character definition, such as
http://blogs.msdn.com/b/zainala/archive/2008/08/17/using-and-escape-clause-in-sql-server-like-query.aspx
select * from MyTable where Description like '|[summary|]%' escape '|'
In your case
select * from 'gallons|/units' escape '|'
You indicate both mysql and sql-server in your tags, so I'm not sure which server support I should be looking for exactly.
In a statement like this;
$sql = "SELECT distinct `term`,count(*) as count
FROM {$temp_table_name}
group by `term` order by count DESC";
What does using the back tick character (`) around the field name 'term' buy me?
Is the usage of back ticks for performance reasons? Or is it for some sort of a SQL injection protection?
Note: After I submit the question, I realized that the backtick character does not show around the field name 'term' - right here on stackoverflow.
I don't know of a way of making it appear here in the question body.
If term is mysql key word, you need to quote it by `, otherwise, it is not necessary.
Ps: distinct is not necessary in your case, because you group by it.
The back-tick is the 'official' identifier quote character.
http://dev.mysql.com/doc/refman/5.0/en/identifiers.html
It allows a wider array of characters in an identifier, as described on the linked documentation.
Backticks just allow the use of spaces or other alternate characters in field names.
I think it's already been pretty well explained here.
When We use a keyword as a table name,field-name in MySQL use backticks, or double-quotes when ANSI_QUOTES is enabled.Other wise it is not necessary.It is not releated to SQL injection protection
When seeing SQL code on the internet and in manuals there seems to vary a lot what is used to signify strings (or at least that's what I think they do?).
Are there any difference between using `, ´, ' or "? Are they all the same? Or do some of them have special meanings? Should some be used in certain cases and others in other cases? What is the deal here?
Backticks (`) are required when identifiers, such as column names, are using names which also happen to be reserved words. For example, since from is a reserved word, you would have to wrap a from column name in backticks, as follows:
SELECT `from`, to FROM messages WHERE to = 'Joe';
Also note how the string in the WHERE clause had to be wrapped in quotes. This is also required.
Further reading:
Reserved Words in MySQL 5.1
`` delimits identifiers and ' and " delimits strings. there are no difference between last two
´ has no meaning in mysql