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;
Related
I ran a SELECT-Statement like the following in Oracle successfully:
SELECT a.*, b.* FROM table_a a, table_b b;
Here I give table table_a the alias 'a' and table_b the alias 'b'.
Then I use the two table aliases in the select list ('a.*, b.*')
with an asterisk for each table alias to select all columns from both
tables.
Sure, I could just use '*' as select list to get all columns
from both tables, but it's about what is valid for the select list
(like here 'a.*, b.*').
I can execute a statement like the one above, but when I look at the syntax diagram for the select list in Oracle's documentation, it seems as it would be not valid to use multiple table aliases in the select list.
The question is, whether it is possible to derive something like ('a.*, b.*') with the syntax diagram for the select list. In the syntax diagram it seems, as if I can just have one table alias in the select, because I can't 'travel back' in the diagram to add a comma and an other table alias.
Syntax diagram: http://docs.oracle.com/database/121/SQLRF/img/select_list.gif
General description for SELECT: http://docs.oracle.com/database/121/SQLRF/statements_10002.htm#SQLRF01702
Yes you can. If you have more values then you just need to traverse back to comma as shown below.
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
Is there a way in SQL server to alias column names for a particular table and store the aliases somewhere such that you can access the aliases while querying? I have a table where I cannot change column names and I am trying to figure out if there is a way to alias them to make them more user friendly.
CREATE VIEW vw_RenameTable
AS
Begin
Select GoodName1 = DumbName1
,GoodName2 = DumbName2
From MyTable
End
A view would be the natural answer to the question. But, if you want to access the columns in the same table, you can use computed columns:
alter table mytable add bettercolumn as [Bad Ugly Name];
You can then use the computed column in a select on the same table.
How can I select the column name and table name from a SQL?
I tried something like this but it didn't work:
select column_name, table_name from (select * from users);
This might sound silly, but I have a list of different SQLs and I need to extract their columns and tables into a list. So some of the statements could me:
select username, password from users
select createdate from userlog
select * from dept
...
If I can select the column name and table name of a select statement, then I should get, say for the first statement, username and password for columns and users for table name. And createdate for column and userlog for table name in the second statement.
Then if it all works, I can then loop through the list of select statements and extract their column and table names.
The below query worked for Oracle database.
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
You can see more about information-schema
Edit:
You may try like this:
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
WHERE TABLE_NAME IN (SELECT ColumnName FROM users)
You need to parse the SQL statement so the SQL engine figures out the columns and datatypes of the columns that the statement returns.
How you do it best depends on what environment you are using. In some programming languages when you create a SqlPreparedStatement or OraCommand or whatever the object may be called, that object may have a metadata collection populated with column information after parsing.
If you are doing it in the database itself, parsing your statement with DBMS_SQL can get you the information you need. See Example 8 in the documentation at this link:
http://docs.oracle.com/database/121/ARPLS/d_sql.htm#ARPLS68205
--
Oh, and this gives you column names of the select statement. The table names I do not know of any way to get easily.
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.