I made a mistake and entered:
SELECT * FROM table LIMIT1
instead of
SELECT * FROM table LIMIT 1 (note the space between LIMIT and 1)
in the CLI of MySQL. I expected to receive some kind of parse error, but I was surprised, because the query returned all of the records in the table. My first thought was "stupid MySQL, I bet that this will return error in PostgreSQL", but PostgreSQL also returned all records. Then tested it with SQLite - with the same result.
After some digging, I realized that it doesn't matter what I enter after the table. As long as there are no WHERE/ORDER/GROUP clauses:
SELECT * FROM table SOMETHING -- works and returns all records in table
SELECT * FROM table WHERE true SOMETHING -- doesn't work - returns parse error
I guess that this is a standardized behavior, but I couldn't find any explanation why's that. Any ideas?
Your first query is equivalent to this query using a table alias:
SELECT * FROM yourtable AS LIMIT1
The AS keyword is optional. The table alias allows you to refer to columns of that table using the alias LIMIT1.foo rather than the original table name. It can be useful to use aliases if you wish to give tables a shorter or a more descriptive alias within a query. It is necessary to use aliases if you join a table to itself.
From the SQL lite documentation:
This is why I want DB engine to force the usage of keyword AS for alias names
http://beyondrelational.com/modules/2/blogs/70/posts/10814/should-alias-names-be-preceded-by-as.aspx
SELECT * FROM table LIMIT1;
LIMIT1 This has taken as alias by SQL, cause LIMIT1 is not a reserved literal of SQL.
Something after table name and that is not a reserved keyword always taken as an table alias by SQL.
SELECT * FROM table LIMIT 1;
When you used LIMIT just after the table name, SQL found that as a reserved keyword and worked for it as per the behavior. IF you want to use reserved key words in query It can be done by putting reserved literals in quotes. like..
SELECT * FROM table `LIMIT`;
OR
SELECT * FROM table `LIMIT 1`;
Now all words covered under `` quotes will treated as user defined.
Commonly we did mistake with date, timestamp, limit etc.. keywords by using them as column names.
Related
I am a newbie in Oracle SQL, though I have experience in SQL Server.
In SQL Server, to select the rows from a table with a particular column in front:
select columnName,* from tableName
In Oracle:
select columnName,* from tableName
gives error ORA-00936: missing expression, as below:
Please guide.
I can't view images, but here's what I think you need:
select t.column_name, t.*
from table_name t
i.e. you should prefix that particular column name with a table alias ("t"), and then use the same alias with the asterisk ("t.*") to retrieve all table columns.
In Oracle, if you need to view a column but also all columns, you need to define an alias for the table.
Select columnName, A.*
from tableName A;
few things we need to keep it in mind
Alias name in sql - used to derive the individual column name via select query
When you are going to use *[select all] you don't have to worry about the alias name
But when you try to pull all the columns and some specific fields you want to filter then you should go for "Alias"
Alias its object key to refer the inter column
select stu.studentName,stu.* from student stu;
Is it possible to avoid specifying a column list in a SQL Server CTE?
I'd like to create a CTE from a table that has many columns so that the structure is identical. There probably is a way to accomplish this without relisting every column name.
I've tried (unsuccessfully):
with pay_cte as
(select * from payments)
select * from pay_cte
I'm encouraged in my quest by this statement in the msdn documentation:
The list of column names is optional only if distinct names for all resulting columns are supplied in the query definition.
https://msdn.microsoft.com/en-us/library/ms175972.aspx
Yes, assuming you mean that you don't have to name every column in the with cte(Col1, Col2) as section.
You can easily try this yourself with a very simple test query along the lines of:
with cte as
(
select *
from sys.tables
)
select *
from cte
I saw this thread:
SELECT
MAX(totalcontracts) AS highest_total
FROM ( SELECT
SuperVisor
,COUNT(ContractNo) AS totalcontracts
FROM Contract
GROUP BY SuperVisor
) AS t
If I delete "as t" line that return me an error. but when I put it back that work fine.
This is temporarly so why do I required to put a name to that subtable?Any sense in that?
Thank you.
In standard SQL a derived table (a subquery you select data from) needs a name:
FROM (<subquery>) [AS] <name>`
(Some DBMS, however, are not compliant with the standard. In Oracle for instance it is not mandatory to give a derived table an alias, but the optional AS is forbidden when you specify one. Other DBMS on the other hand may require the AS although the SQL standard specifies it as optional.)
No, there isn't a real logic necessity here.
Oracle for instance does not force it
select * from (select * from dual);
Nor SQLite
select * from (select 1)
As #jarlh mentioned, if you're using some database systems, in order to use the result from any nested subquery you need to give that result-set a name (or alias), which is why you need to put a name / letter / character after you close the paranthesis.
The AS keyword is not mandatory, but the name is.
We have an application which indexes data using user-written SQL statements. We place those statements within parenthesis so we can limit that query to a certain criteria. For example:
select * from (select F_Name from table_1)q where ID > 25
Though we have discovered that this format does not function using a Sybase database. Reporting a syntax error around the parenthesis. I've tried playing around on a test instance but haven't been able to find a way to achieve this result. I'm not directly involved in the development and my SQL knowledge is limited. I'm assuming the 'q' is to give the subresult an alias for the application to use.
Does Sybase have a specific syntax? If so, how could this query be adapted for it?
Thanks in advance.
Sybase ASE is case sensitive w.r.t. all identifiers and the query shall work:
as per #HannoBinder query :
select id from ... is not the same as select ID from... so make sure of the case.
Also make sure that the column ID is returned by the Q query in order to be used in where clause .
If the table and column names are in Upper case the following query shall work:
select * from (select F_NAME, ID from TABLE_1) Q where ID > 25
I know you cannot use a alias column in the where clause for T-SQL; however, has Microsoft provided some kind of workaround for this?
Related Questions:
Unknown Column In Where Clause
Can you use an alias in the WHERE clause in mysql?
“Invalid column name” error on SQL statement from OpenQuery results
One workaround would be to use a derived table.
For example:
select *
from
(
select a + b as aliased_column
from table
) dt
where dt.aliased_column = something.
I hope this helps.
Depending on what you are aliasing, you could turn it into a user defined function and reference that in both places. Otherwise your copying the aliased code in several places, which tends to become very ugly and means updating 3+ spots if you are also ordering on that column.