I've noticed that Visual Studio 2008 is placing square brackets around column names in sql. Do the brackets offer any advantage? When I hand code T-SQL I've never bothered with them.
Example:
Visual Studio:
SELECT [column1], [column2] etc...
My own way:
SELECT column1, column2 etc...
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.
They're handy if your columns have the same names as SQL keywords, or have spaces in them.
Example:
create table test ( id int, user varchar(20) )
Oh no! Incorrect syntax near the keyword 'user'.
But this:
create table test ( id int, [user] varchar(20) )
Works fine.
They are useful if you are (for some reason) using column names with certain characters for example.
Select First Name From People
would not work, but putting square brackets around the column name would work
Select [First Name] From People
In short, it's a way of explicitly declaring a object name; column, table, database, user or server.
During the dark ages of SQL in the 1990s it was a good practice as the SQL designers were trying to add each word in the dictionary as keyword for endless avalanche of new features and they called it the SQL3 draft.
So it keeps forward compatibility.
And i found that it has another nice side effect, it helps a lot when you use grep in code reviews and refactoring.
Regardless of following a naming convention that avoids using reserved words, Microsoft does add new reserved words. Using brackets allows your code to be upgraded to a new SQL Server version, without first needing to edit Microsoft's newly reserved words out of your client code. That editing can be a significant concern. It may cause your project to be prematurely retired....
Brackets can also be useful when you want to Replace All in a script. If your batch contains a variable named #String and a column named [String], you can rename the column to [NewString], without renaming #String to #NewString.
Column names can contain characters and reserved words that will confuse the query execution engine, so placing brackets around them at all times prevents this from happening. Easier than checking for an issue and then dealing with it, I guess.
The brackets can be used when column names are reserved words.
If you are programatically generating the SQL statement from a collection of column names you don't control, then you can avoid problems by always using the brackets.
In addition
Some Sharepoint databases contain hyphens in their names. Using square brackets in SQL Statements allow the names to be parsed correctly.
They are useful to identify each elements in SQL.
For example:
CREATE TABLE SchemaName.TableName (
This would actually create a table by the name SchemaName.TableName under default dbo schema even though the intention might be to create the table inside the SchemaName schema.
The correct way would be the following:
CREATE TABLE [SchemaName].[TableName] (
Now it it knows what is the table name and in which schema should it be created in (rightly in the SchemaName schema and not in the default dbo schema)
I believe it adds them there for consistency... they're only required when you have a space or special character in the column name, but it's cleaner to just include them all the time when the IDE generates SQL.
Related
This question's answers are a community effort. Edit existing answers to improve this post. It is not currently accepting new answers or interactions.
I'm trying to execute a simple MySQL query as below:
INSERT INTO user_details (username, location, key)
VALUES ('Tim', 'Florida', 42)
But I'm getting the following error:
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key) VALUES ('Tim', 'Florida', 42)' at line 1
How can I fix the issue?
The Problem
In MySQL, certain words like SELECT, INSERT, DELETE etc. are reserved words. Since they have a special meaning, MySQL treats it as a syntax error whenever you use them as a table name, column name, or other kind of identifier - unless you surround the identifier with backticks.
As noted in the official docs, in section 10.2 Schema Object Names (emphasis added):
Certain objects within MySQL, including database, table, index, column, alias, view, stored procedure, partition, tablespace, and other object names are known as identifiers.
...
If an identifier contains special characters or is a reserved word, you must quote it whenever you refer to it.
...
The identifier quote character is the backtick ("`"):
A complete list of keywords and reserved words can be found in section 10.3 Keywords and Reserved Words. In that page, words followed by "(R)" are reserved words. Some reserved words are listed below, including many that tend to cause this issue.
ADD
AND
BEFORE
BY
CALL
CASE
CONDITION
DELETE
DESC
DESCRIBE
FROM
GROUP
IN
INDEX
INSERT
INTERVAL
IS
KEY
LIKE
LIMIT
LONG
MATCH
NOT
OPTION
OR
ORDER
PARTITION
RANK
REFERENCES
SELECT
TABLE
TO
UPDATE
WHERE
The Solution
You have two options.
1. Don't use reserved words as identifiers
The simplest solution is simply to avoid using reserved words as identifiers. You can probably find another reasonable name for your column that is not a reserved word.
Doing this has a couple of advantages:
It eliminates the possibility that you or another developer using your database will accidentally write a syntax error due to forgetting - or not knowing - that a particular identifier is a reserved word. There are many reserved words in MySQL and most developers are unlikely to know all of them. By not using these words in the first place, you avoid leaving traps for yourself or future developers.
The means of quoting identifiers differs between SQL dialects. While MySQL uses backticks for quoting identifiers by default, ANSI-compliant SQL (and indeed MySQL in ANSI SQL mode, as noted here) uses double quotes for quoting identifiers. As such, queries that quote identifiers with backticks are less easily portable to other SQL dialects.
Purely for the sake of reducing the risk of future mistakes, this is usually a wiser course of action than backtick-quoting the identifier.
2. Use backticks
If renaming the table or column isn't possible, wrap the offending identifier in backticks (`) as described in the earlier quote from 10.2 Schema Object Names.
An example to demonstrate the usage (taken from 10.3 Keywords and Reserved Words):
mysql> CREATE TABLE interval (begin INT, end INT);
ERROR 1064 (42000): You have an error in your SQL syntax.
near 'interval (begin INT, end INT)'
mysql> CREATE TABLE `interval` (begin INT, end INT);
Query OK, 0 rows affected (0.01 sec)
Similarly, the query from the question can be fixed by wrapping the keyword key in backticks, as shown below:
INSERT INTO user_details (username, location, `key`)
VALUES ('Tim', 'Florida', 42)"; ^ ^
This question's answers are a community effort. Edit existing answers to improve this post. It is not currently accepting new answers or interactions.
I'm trying to execute a simple MySQL query as below:
INSERT INTO user_details (username, location, key)
VALUES ('Tim', 'Florida', 42)
But I'm getting the following error:
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key) VALUES ('Tim', 'Florida', 42)' at line 1
How can I fix the issue?
The Problem
In MySQL, certain words like SELECT, INSERT, DELETE etc. are reserved words. Since they have a special meaning, MySQL treats it as a syntax error whenever you use them as a table name, column name, or other kind of identifier - unless you surround the identifier with backticks.
As noted in the official docs, in section 10.2 Schema Object Names (emphasis added):
Certain objects within MySQL, including database, table, index, column, alias, view, stored procedure, partition, tablespace, and other object names are known as identifiers.
...
If an identifier contains special characters or is a reserved word, you must quote it whenever you refer to it.
...
The identifier quote character is the backtick ("`"):
A complete list of keywords and reserved words can be found in section 10.3 Keywords and Reserved Words. In that page, words followed by "(R)" are reserved words. Some reserved words are listed below, including many that tend to cause this issue.
ADD
AND
BEFORE
BY
CALL
CASE
CONDITION
DELETE
DESC
DESCRIBE
FROM
GROUP
IN
INDEX
INSERT
INTERVAL
IS
KEY
LIKE
LIMIT
LONG
MATCH
NOT
OPTION
OR
ORDER
PARTITION
RANK
REFERENCES
SELECT
TABLE
TO
UPDATE
WHERE
The Solution
You have two options.
1. Don't use reserved words as identifiers
The simplest solution is simply to avoid using reserved words as identifiers. You can probably find another reasonable name for your column that is not a reserved word.
Doing this has a couple of advantages:
It eliminates the possibility that you or another developer using your database will accidentally write a syntax error due to forgetting - or not knowing - that a particular identifier is a reserved word. There are many reserved words in MySQL and most developers are unlikely to know all of them. By not using these words in the first place, you avoid leaving traps for yourself or future developers.
The means of quoting identifiers differs between SQL dialects. While MySQL uses backticks for quoting identifiers by default, ANSI-compliant SQL (and indeed MySQL in ANSI SQL mode, as noted here) uses double quotes for quoting identifiers. As such, queries that quote identifiers with backticks are less easily portable to other SQL dialects.
Purely for the sake of reducing the risk of future mistakes, this is usually a wiser course of action than backtick-quoting the identifier.
2. Use backticks
If renaming the table or column isn't possible, wrap the offending identifier in backticks (`) as described in the earlier quote from 10.2 Schema Object Names.
An example to demonstrate the usage (taken from 10.3 Keywords and Reserved Words):
mysql> CREATE TABLE interval (begin INT, end INT);
ERROR 1064 (42000): You have an error in your SQL syntax.
near 'interval (begin INT, end INT)'
mysql> CREATE TABLE `interval` (begin INT, end INT);
Query OK, 0 rows affected (0.01 sec)
Similarly, the query from the question can be fixed by wrapping the keyword key in backticks, as shown below:
INSERT INTO user_details (username, location, `key`)
VALUES ('Tim', 'Florida', 42)"; ^ ^
I have to remove the particular value from the sentence which is stored in SQL database. Sentence will look like this:
1 Payments:ihj - CHENNAI-HIRE:54005-TN69AZ54008,4021-TN69AZ54005
2 Payments:ihj - CHENNAI-HIRE:54004-TN69AZ54008,4021-TN69AZ54005,54005-TN69AZ54008
In above sentence 54004 is the number which I will pass as parameter to SQL. This is the number which I want to remove from this line but same number is present in this line as TN69AZ54005. This number should not be disturbed, and in another payment we have same amount in another place. Can anyone help on this?
I tried with this sql query
declare #text int=4019
select SUBSTRING(notes,CHARINDEX(cast(#text as varchar),notes),
len(notes)-CHARINDEX(',',notes)+1)
from Accounts.TransactionNotes
where TransactionID=1978
If I use this query it will affect including this line TN69AZ54005
I can see that you've included a C# tag into your question. Then probably the easiest way is just to select all necessary rows using your app, then iterate through them and change the strings to your needs (using eg. PHP preg_replace() equivalent) and update the SQL rows.
I believe that is the easiest way, not really SQL solution but still...
update <table> set notes = replace(notes, 'HIRE:'+ str(<inputparam>),'HIRE:') where transactionid=<transactionid>
update <table> set notes = replace(notes, ','+ str(<inputparam>),',') where transactionid=<transactionid>
You will need to find something to prefix your inputpram value, like in above example I am using "HIRE:" or a comma.
Another way could be to use REGEXP to find the whole word, then one one query would suffice. But I haven't tried it.
The problem here is not the query but the person who designed the
database.
I`m not sure is it this what you want but I will past my code. :)
-- for test create #temp
SELECT
A.DATA
INTO #Temp
FROM
(
SELECT 'Payments:ihj - CHENNAI-HIRE:54005-TN69AZ54008,4021-TN69AZ54005' AS DATA
UNION
SELECT 'Payments:ihj - CHENNAI-HIRE:54004-TN69AZ54008,4021-TN69AZ54005,54005-TN69AZ54008' AS DATA
) AS A
GO
-- this you want?
UPDATE #Temp
SET DATA = REPLACE(DATA,'54004','')
GO
-- select changed data
SELECT * FROM #Temp
I'm using NHibernate mapping by code with naming conventions to map my entities. Now I have following error
SQL error - Incorrect syntax near the keyword 'User'.:
I know this is reserved word and I'm wonder how can I use this name (User) as entity name in mapping by conventions.
You can use it by wrapping it around square brackets as it is a reserved keyword in SQL SERVER:
[User]
The word user is a reserved word in SQL Server. If you need to use it as a column name, put brackets around it. This goes for all table names and other user-defined names that happen to collide with keywords,
Example:
Select * from tbl where [User] = 'xyz'
The correct way to deal with this in NHibernate is using SQL Quoted Identifiers.
Just wrap the table or column name in backticks and the Dialect will take care of using the right symbol for your database.
To make things easier, NHibernate provides a configuration setting that does this for you: set hbm2ddl.keywords="auto-quote" in an xml config file, or call AutoQuoteKeywords() when using loquacious.
If the brackets don't work, try this:
"`User`"
I am a PHP/MySQL developer, slowly venturing into the realm of C#/SQL Server and I am having a problem in C# when it comes to reading an SQL Server query that joins two tables.
Given the two tables:
TableA:
int:id
VARCHAR(50):name
int:b_id
TableB:
int:id
VARCHAR(50):name
And given the query
SELECT * FROM TableA,TableB WHERE TableA.b_id = TableB.id;
Now in C# I normally read query data in the following fashion:
SqlDataReader data_reader= sql_command.ExecuteReader();
data_reader["Field"];
Except in this case I need to differentiate from TableA's name column, and TableB's name column.
In PHP I would simply ask for the field "TableA.name" or "TableB.name" accordingly but when I try something like
data_reader["TableB.name"];
in C#, my code errors out.
How can fix this? And how can I read a query on multiple tables in C#?
The result set only sees the returned data/column names, not the underlying table. Change your query to something like
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...
Then you can refer to the fields like this:
data_reader["Name_TA"];
To those posting that it is wrong to use "SELECT *", I strongly disagree with you. There are many real world cases where a SELECT * is necessary. Your absolute statements about its "wrong" use may be leading someone astray from what is a legitimate solution.
The problem here does not lie with the use of SELECT *, but with a constraint in ADO.NET.
As the OP points out, in PHP you can index a data row via the "TABLE.COLUMN" syntax, which is also how raw SQL handles column name conflicts:
SELECT table1.ID, table2.ID FROM table1, table;
Why DataReader is not implemented this way I do not know...
That said, a solution to be used could build your SQL statement dynamically by:
querying the schema of the tables you're selecting from
build your SELECT clause by iterating through the column names in the schema
In this way you could build a query like the following without having to know what columns currently exist in the schema for the tables you're selecting from
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...
You could try reading the values by index (a number) rather than by key.
name = data_reader[4];
You will have to experiment to see how the numbers correspond.
Welcome to the real world. In the real world, we don't use "SELECT *". Specify which columns you want, from which tables, and with which alias, if required.
Although it is better to use a column list to remove duplicate columns, if for any reason you want *****, then just use
rdr.item("duplicate_column_name")
This will return the first column value, since the inner join will have the same values in both identical columns, so this will accomplish the task.
Ideally, you should never have duplicate column names, across a database schema. So if you can rename your schema to not have conflicting names.
That rule is for this very situation. Once you've done your join, it is just a new recordset, and generally the table names do go with it.