I am trying to do a query in a SQLite database equivalent to this:
SELECT act_unit FROM processes WHERE process='processname'
but using the keyword values, so I can specify the name, which is stored in a variable (I am actually running the query in a Jupyter notebook). I've used successfully the keyword values in insert statements, but I do not know how to do it here. I tried several combinations like this one
SELECT act_unit from processes WHERE process=values,('processname')
but I can't figure out how to do it properly.
From the SQLite documentation: https://www.sqlite.org/lang_keywords.html
It would be SELECT act_unit from processes WHERE process="values",('processname')
If you want to use a keyword as a name, you need to quote it. There
are four ways of quoting keywords in SQLite:
'keyword' A keyword in single quotes is a string literal.
"keyword" A keyword in double-quotes is an identifier.
[keyword] A
keyword enclosed in square brackets is an identifier. This is not
standard SQL. This quoting mechanism is used by MS Access and SQL
Server and is included in SQLite for compatibility.
keyword A
keyword enclosed in grave accents (ASCII code 96) is an identifier.
This is not standard SQL. This quoting mechanism is used by MySQL and
is included in SQLite for compatibility.
Related
I have table named References in SQLite, so I can't target it, it seems. SQLite studio I use to edit databases throws an error.
Is there a way to escape database name?
The query is:
UPDATE References
SET DateTimeLastEdited = datetime('now', 'localtime')
WHERE NewsItemID = old.NewsItemID;
(This is part of the trigger I am making.)
You can escape table names with double quotes:
UPDATE "References" SET DateTimeLastEdited = datetime('now', 'localtime') WHERE NewsItemID = old.NewsItemID;
Depending on what you want to escape, you need to use different delimiters:
If you want to use a keyword as a name, you need to quote it. There
are four ways of quoting keywords in SQLite:
'keyword' A keyword in single quotes is a string literal.
"keyword" A keyword in double-quotes is an identifier.
[keyword] A
keyword enclosed in square brackets is an identifier. This is not
standard SQL. This quoting mechanism is used by MS Access and SQL
Server and is included in SQLite for compatibility.
`keyword` A
keyword enclosed in grave accents (ASCII code 96) is an identifier.
This is not standard SQL. This quoting mechanism is used by MySQL and
is included in SQLite for compatibility.
From SQLite documentation
Hi I try to use SQLite Parameterized query
but in the column name is a DOT (.)
INSERT INTO Data (`test.1`, `test.2`, `test.3`) VALUES (#test.1, #test.3,#test.3)
Returns
"SQL logic error or missing database near ".": syntax error"
INSERT INTO Data (`test.1`, `test.2`, `test.3`) VALUES ([#test.1], [#test.3],[#test.3])
Returns
"SQL logic error or missing database
no such column: #test.1"
how can i escape the dot and still use the names as parameters!?
The "proper" escape character in SQLite is double quotes:
INSERT INTO Data("test.1", "test.2", "Test.3")
VALUES ([#test1], [#test3], [#test3])
Leave the . out of the parameter name -- presumably, you have control over that.
SQLite explicitly supports the backtick for compatibility with MySQL and the square braces for compatibility with MS Access and SQL Server. (As you can see in the documentation.)
I have a very simple SQL statement
SELECT * FROM Table;
but, my query engine returns a syntax error. Why?
Error Details:
An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in >System.Data.dll
Additional information: Incorrect syntax near the keyword 'Table'.
How is this possible? I checked the connection string and it is correct.
I checked my table name and it is also correct.
What I am doing wrong?
Okay, Table is a reserved keyword in all variants of SQL.
If you want to call a table Table, and use it in a statement, you have to tell your sql engine that it is an identifier. To do this you need to use Identifier Qualifiers.
for (MS SQL Server) TSQL use square brackets
SELECT * FROM [Table];
for MySQL use `
SELECT * FROM `Table`;
for Oracle and PostgreSQL use quotation marks,
these are standards compliant.
SELECT * FROM "Table";
for SQLite you can use any of the above, but quotation marks are prefered.
The Identifier Qualifiers tell the engine that this is an identifier (the name of an object.) Not the name of a keyword, even if they happen to be the same. Without your guidance the query engine can get confused and report an error, or worse, do something unexpected.
Using Identifier Qualifiers is good practice, even if the identifers are not keywords.
They better define statements for all parsers, including the fleshy kind.
Naming objects after keywords is generally considered bad practice. So you should try to avoid making identifers the same as keywords. The occasions when a reserved keyword is descriptive of the contents of a table are rare, see the footnote.
e.g. your table is not a Table of tables.
The problem and advice is not limited to Tables, Identifiers are required for all database objects inluding Schema, Views and the many types that exist, standard and vendor-specific.
Another form of good practice is to prefix Table indentifiers with a Schema identifier, this helps the query engine a little.
When including the Schema identifier, the identifer should be qualified,
for (MS SQL Server) TSQL use square brackets
SELECT * FROM [dbo].[Table];
for MySQL use `
SELECT * FROM `dbo`.`Table`;
for Oracle, PostgreSQL and SQLite use quotation marks
SELECT * FROM "dbo"."Table";
even if your Schema is not named after a keyword, as should be the case.
For your reference, to help you avoid conflicts.
A list of TSQL Reserverd Keywords.
A list of MySQl Reserved Keywords.
A list of Oracle Reserved Keywords.
A list of SQLite Reserved Keywords.
A list of PostgreSQL Reserved Keywords.
Notable "gotcha's" include USER and ERROR, which seem to come up when designing systems.
Footnote:
There are occasions when using reseved words for object names may be semantically correct.
Consider the contrived example of an information system for a furniture shop. In this scenario, a table of tables (kitchen, garden, dining, apothecary etc.) may be correct. So, you could argue Table was the correct identifier.
If you always use Identifier Qualifiers, you won't get burned.
If you are using SQL server you need to wrap table in brackets [] as table is keyword in SQL Server
SELECT * FROM [Table]
I have SQL Server 2008 Express Edition installed and is my first time running a SQL query. I noticed that if I select to display the top 1000 rows that the query places brackets [] around the name of the database and its respective columns.
Why are there brackets around the name of the database and columns?
Is there a need to have these and if so when?
I just posted this answer on dba.stack.
They escape names that are not "friendly" - they can be useful if your database names contain special characters (such as spaces, dots or dashes) or represent SQL keywords (such as USE or DATABASE :-)). Without the square brackets, a query like this will fail:
SELECT column FROM database.dbo.table;
However if you write the query this way, the keywords are ignored:
SELECT [column] FROM [database].dbo.[table];
When building scripts or writing solutions that generate scripts from metadata (e.g. generating a script of all tables or all indexes), I always wrap entity names in square brackets so that they will work regardless of what kind of wonky names have been implemented (I am not always doing this for systems I control). You can do this easily using QUOTENAME function, e.g.:
SELECT QUOTENAME('table'), QUOTENAME('column'), QUOTENAME('database');
Results:
[table] [column] [database]
If you search my answers here for QUOTENAME you will find that I use it in a lot of scripts where I'm helping folks automate script generation or building dynamic SQL. Without the square brackets, a lot of people would run into issues running the scripts.
Enclosing a string in square braces is tells SQL Server that it should not try to parse whatever is inside them. This allows you to do use things like SQL reserved words (select, table, return, etc.) as well as spaces in identifiers. They are only required in those cases, but they are not harmful in any case.
No there isn't, but it ensures that if you had a db, table or column named as a reserved or keyword, for example date, that it wouldn't be confused with that keyword.
when I write a sql statement in php, i usualy write it as below
SELECT COUNT(*) FROM catalogsearch_query AS main_table
but I found that some people write sql statement like
SELECT COUNT(*) FROM `catalogsearch_query` AS `main_table`
do I have to use ` ?
You don't have to use backticks. However when you're using reserved keywords as table or field names, then you have to enclose them in backticks for them to work.
From MySql docs:
Database, table, index, column, and alias names are identifiers. An identifier may be quoted or unquoted. If an identifier contains special characters or is a reserved word, you must quote it whenever you refer to it.
We use the backtick ` for quoting.