Is the 'AS' keyword required in Oracle to define an alias name for a column in a SELECT statement?
I noticed that
SELECT column_name AS "alias"
is the same as
SELECT column_name "alias"
I am wondering what the consequences are of defining a column alias in the latter way.
According to the select_list Oracle select documentation the AS is optional.
As a personal note I think it is easier to read with the AS
(Tested on Oracle 11g)
About AS:
When used on result column, AS is optional.
When used on table name, AS shouldn't be added, otherwise it's an error.
About double quote:
It's optional & valid for both result column & table name.
e.g
-- 'AS' is optional for result column
select (1+1) as result from dual;
select (1+1) result from dual;
-- 'AS' shouldn't be used for table name
select 'hi' from dual d;
-- Adding double quotes for alias name is optional, but valid for both result column & table name,
select (1+1) as "result" from dual;
select (1+1) "result" from dual;
select 'hi' from dual "d";
AS without double quotations is good.
SELECT employee_id,department_id AS department
FROM employees
order by department
--ok--
SELECT employee_id,department_id AS "department"
FROM employees
order by department
--error on oracle--
so better to use AS without double quotation if you use ORDER BY clause
Both are correct. Oracle allows the use of both.
My conclusion is that（Tested on 12c）:
AS is always optional, either with or without ""; AS makes no difference (column alias only, you can not use AS preceding table alias)
However, with or without "" does make difference because "" lets lower case possible for an alias
thus :
SELECT {T / t} FROM (SELECT 1 AS T FROM DUAL); -- Correct
SELECT "tEST" FROM (SELECT 1 AS "tEST" FROM DUAL); -- Correct
SELECT {"TEST" / tEST} FROM (SELECT 1 AS "tEST" FROM DUAL ); -- Incorrect
SELECT test_value AS "doggy" FROM test ORDER BY "doggy"; --Correct
SELECT test_value AS "doggy" FROM test WHERE "doggy" IS NOT NULL; --You can not do this, column alias not supported in WHERE & HAVING
SELECT * FROM test "doggy" WHERE "doggy".test_value IS NOT NULL; -- Do not use AS preceding table alias
So, the reason why USING AS AND "" causes problem is NOT AS
Note: "" double quotes are required if alias contains space OR if it contains lower-case characters and MUST show-up in Result set as lower-case chars. In all other scenarios its OPTIONAL and can be ignored.
The quotes are required when we have a space in Alias Name like
SELECT employee_id,department_id AS "Department ID"
FROM employees
order by department
There is no difference between both, AS is just a more explicit way of mentioning the alias which is good because some dependent libraries depends on this small keyword. e.g. JDBC 4.0. Depend on use of it, different behaviour can be observed.
See this. I would always suggest to use the full form of semantic to avoid such issues.
Related
WHERE ("z" = 'abc')) "test"
You need to show the entire query, but "test" is not part of the where clause. It looks like a table alias or a column alias. For example:
select "test".*
from (select t.*
from t
where ("z" = 'abc')
) "test"
I do not advise escaping column aliases or table aliases, but your code seems to be doing that.
I am currently working with a MS SQL database on Windows 2012 Server
I need to query only 1 column from a table that I only have access to read, not make any kind of changes.
Problem is that the name of the column is "Value"
My code is this:
SELECT 'Value' FROM table
If I add
`ORDER BY 'Value'`
The issue is that the query is returning an empty list of results.
Things I've tried already
I tried replacing ' with `"' but this didn't work either.
I also tried writing SELECT * instead of SELECT VALUE
Using the table name in the SELECT or ORDER clauses again didn't help
You are claiming that this query:
SELECT 'Value'
FROM table
ORDER BY 'Value'
Is returning no rows. That's not quite correct. It is returning an error because SQL Server does not allow constant expressions as keys for ORDER BY (or GROUP BY for that matter).
Do not use single quotes. In this case:
SELECT 'Value' as val
FROM table
ORDER BY val;
Or, if value is a column in the table:
SELECT t.Value
FROM table t
ORDER BY t.Value;
Value is not a reserved word in SQL Server, but if it were, you could escape it:
SELECT t.[Value]
FROM table t
ORDER BY t.[Value];
it looks like your table has null values. and because of the order by all null values come first.
try to add filter like this
select Value FROM table
where Value is not null and Value <> ''
order by Value
I was going through some old-ish SQL code someone else had written that I couldn't quite understand. I have simplified its structure here, but if anyone can walk me through what exactly is going on, that would be appreciated! You may ignore the specific column operations as they were just examples.
SELECT table.*,
column1 - column2
AS 'col1 - col2',
...
columnn
AS 'coln'
FROM
(SELECT
...
) table
What I don't understand is the final line. I am assuming it is the definition of "table" in the FROM (SELECT ...) part, and the ) table part indicates the name of the defined table.
Thanks in advance!
An inner select needs an alias name
select alias_name.* from
(
select * from some_table ...
) alias_name
The 'table' in that final line is an alias for the subquery.
In T-SQL it is AFAIK mandatory to specify an alias for a subquery if you're selecting from a subquery.
You can name the alias whathever you want. It is perfectly ok to use it like this
select * from
( select * from ... ) as X
(The as keyword is not mandatory, but I always specify the alias-name using 'as').
Sorry if this a duplicate, but i haven't found one. Why can't i use my column alias defined in the SELECT from the ORDER BY when i use CASE?
Consider this simple query:
SELECT NewValue=CASE WHEN Value IS NULL THEN '<Null-Value>' ELSE Value END
FROM dbo.TableA
ORDER BY CASE WHEN NewValue='<Null-Value>' THEN 1 ELSE 0 END
The result is an error:
Invalid column name 'NewValue'
Here's a sql-fiddle. (Replace the ORDER BY NewValue with the CASE WHEN... that´'s commented out)
I know i can use ORDER BY CASE WHEN Value IS NULL THEN 1 ELSE 0 END like here in this case but actually the query is more complex and i want to keep it as readable as possible. Do i have to use a sub-query or CTE instead, if so why is that so?
Update as Mikael Eriksson has commented any expression in combination with an alias is not allowed. So even this (pointless query) fails for the same reason:
SELECT '' As Empty
FROM dbo.TableA
ORDER BY Empty + ''
Result:
Invalid column name 'Empty'.
So an alias is allowed in an ORDER BY and also an expression but not both. Why, is it too difficult to implement? Since i'm mainly a programmer i think of aliases as variables which could simple be used in an expression.
This has to do with how a SQL dbms resolves ambiguous names.
I haven't yet tracked down this behavior in the SQL standards, but it seems to be consistent across platforms. Here's what's happening.
create table test (
col_1 integer,
col_2 integer
);
insert into test (col_1, col_2) values
(1, 3),
(2, 2),
(3, 1);
Alias "col_1" as "col_2", and use the alias in the ORDER BY clause. The dbms resolves "col_2" in the ORDER BY as an alias for "col_1", and sorts by the values in "test"."col_1".
select col_1 as col_2
from test
order by col_2;
col_2
--
1
2
3
Again, alias "col_1" as "col_2", but use an expression in the ORDER BY clause. The dbms resolves "col_2" not as an alias for "col_1", but as the column "test"."col_2". It sorts by the values in "test"."col_2".
select col_1 as col_2
from test
order by (col_2 || '');
col_2
--
3
2
1
So in your case, your query fails because the dbms wants to resolve "NewValue" in the expression as a column name in a base table. But it's not; it's a column alias.
PostgreSQL
This behavior is documented in PostgreSQL in the section Sorting Rows. Their stated rationale is to reduce ambiguity.
Note that an output column name has to stand alone, that is, it cannot be used in an expression — for example, this is not correct:
SELECT a + b AS sum, c FROM table1 ORDER BY sum + c; -- wrong
This restriction is made to reduce ambiguity. There is still ambiguity if an ORDER BY item is a simple name that could match either an output column name or a column from the table expression. The output column is used in such cases. This would only cause confusion if you use AS to rename an output column to match some other table column's name.
Documentation error in SQL Server 2008
A slightly different issue with respect to aliases in the ORDER BY clause.
If column names are aliased in the SELECT list, only the alias name can be used in the ORDER BY clause.
Unless I'm insufficiently caffeinated, that's not true at all. This statement sorts by "test"."col_1" in both SQL Server 2008 and SQL Server 2012.
select col_1 as col_2
from test
order by col_1;
It seems this limitation is related to another limitation in which "column aliases can't be referenced in same SELECT list". For example, this query:
SELECT Col1 AS ColAlias1 FROM T ORDER BY ColAlias1
Can be translated to:
SELECT Col1 AS ColAlias1 FROM T ORDER BY 1
Which is a legal query. But this query:
SELECT Col1 AS ColAlias1 FROM T ORDER BY ColAlias1 + ' '
Should be translated to:
SELECT Col1 AS ColAlias1, ColAlias1 + ' ' FROM T ORDER BY 2
Which will raise the error:
Unknown column 'ColAlias1' in 'field list'
And finally it seems these are because of SQL standard behaviours not an impossibility in implementation.
More info at: Here
Note: The last query can be executed by MS Access without error but will raise the mentioned error with SQL Server.
You could try something like:
select NewValue from (
SELECT (CASE WHEN Value IS NULL THEN '<Null-Value>' ELSE Value END ) as NewValue,
( CASE WHEN NewValue='<Null-Value>' THEN 1 ELSE 0 END) as ValOrder
FROM dbo.TableA
GROUP BY Value
) t
ORDER BY ValOrder
I have a table that has a column named RANK which is a keyword in Oracle.
Now I need to insert data in this table :
insert into mytbl (RANK)
select RANK from other_table
when executing this query I got the following error :
ORA-00907: missing right parenthesis
How does one escape a keyword?
Oracle uses double quotes " to escape reserved words.
insert into mytbl ("RANK")
select "RANK"
from other_table
One other note, Oracle requires correct case as well.
First of all, You shall not use reserved keywords as column name and table name.
Oracle uses Double quotes " to parse reserved keywords so you can parse the keywords
by placing it in doubles quotes "".
insert into mytbl ("RANK")
select "RANK"
from other_table
In my case, there is , in my query.
UPDATE SCHEMA.TABLE SET PART_NO = '1S7F530400', WHERE PART_NO = '1S7?F5304?00';
This should be:
UPDATE SCHEMA.TABLE SET PART_NO = '1S7F530400' WHERE PART_NO = '1S7?F5304?00';
It has been mentioned before, but to emphasize, one must exactly match the case in all uses. When I needed to extract the GROUP column and order it, "Group" did not work. It had to be "GROUP" in both cases such as
select "GROUP" from PICKLIST
order by "GROUP"