I'm given the following statement:
SELECT id FROM record_database WHERE id = <up to me to complete the statement>
The record database has different fields, among which are id and name.
I'm supposed to complete this select statement so that it displays all the ids and all the corresponding names side by side, and this should be done using this one line of SQL code. A hint was given that UNION or OR can be used.
I tried variations of the following:
SELECT id FROM record_database WHERE id = '*'
UNION
SELECT name FROM record_database WHERE name = '*';
But none of these worked. I tried doing this with AND, tried using display columns, but those didn't work either.
Any help would be appreciated.
This smells a great deal like homework, so I won't offer a complete answer, but you can't just union queries that return dissimilar result sets. I'm inferring that ID is an integer while NAME is some varchar, which won't union as you've listed in your hint.
When you say "complete," are you restricted to adding things to the end? If so, its a non-starter. You can't increase the list of fields being returned merely by adding things to the "WHERE" clause. You need to add things to the actual field list to get them to be returned, so you might clarify whether you are truly restricted to appending to the query you;ve given.
If you are looking for:
id
name
id next
name next
Then use this trick:
SELECT col2
FROM (
SELECT id, col2=convert ( varchar (size of name field),id)
FROM table
WHERE ....
UNION ALL
SELECT id, name
FROM table
WHERE ....
)
ORDER BY id
This order by will bring id and name side by side and col2 will contain id in first row and name in second row.
Cheating. Make the select return 0 rows and add another one that will show 2 columns. All in one and the same line:
SELECT id FROM record_database WHERE id = NULL;SELECT id,name FROM record_database;
No more time should be wasted on silly problems like this.
If both id and name are char (or varchar), you could also do this, concatting the two columns into one:
SELECT id FROM record_database WHERE id = NULL
UNION ALL
SELECT id || '--' || name FROM record_database ;
The id || '--' || name part differs from one DBMS to another. In some, the + is the concat operator, in others there are special functions. So you may need to use:
id + '--' + name
or:
CONCAT(id, '--', name)
Try this
SELECT * FROM record_database WHERE id = '*' OR name = '*'
Related
I'm just taking a look at the following query
select * from tablename
where id like '%%';
So that it can handle parameters to include all of the data or filtered data like bellow
select * from tablename
where id like '%1%';
Which is fine for most parameters I use but this seems wrong for an ID because it will return all data that has IDs containing 1 which I don't want
To get around this I can only append the where clause if the ID is given but that seems like a pain in the butt
Is it possible to use a different type of where clause so that a wildcard can be used in a where equals clause instead of a where like clause, example
select * from tablename
where id = '*';
So that the same query can be used to return all or filtered data? Pass parameter '*' for all or parameter '1' for ID 1 specifically
(I'm not sure if it matters for this case but I'm using PostgreSQL 9.6.12 in this example)
This would often be expressed as:
where (id = :id or :id is null)
null is the "magic" value that represents all rows.
Is it possible in PostgreSQL to SELECT * from a table, but add a condition to one column in that result and overwrite it? I'll explain easier with a code example of what I'm trying to do (pseudo code)
SELECT
*,
CASE
WHEN column_name=1 THEN 'one'
WHEN column_name=2 THEN 'two'
ELSE 'other'
END AS column_name
FROM table
and this returns something like:
id | name | column_name | created_at
------------------------------------
1 | Title | one | 123456789
So basically, I want to get every column without having to type each column out, but specifically alter the value of one column in the result based on some condition.
=== UPDATE ======
A little more clarification on what I am doing.
I'm writing a plpgsql function that returns a type of, for the above example RETURNS schema.table. This is then (via Postgraphile) accessed through a GraphQL endpoint and returned to our app, that is all typed with TypeScript using codegen.
So in essence, the column name needs to be 1. the same name and 2. not an alias name, as Postgraphile/GraphQL won't know this value so will be omitted.
=== UPDATE 2 ======
Ok I have done it now, but a different way. I looked at it and realised there is a easier way for me to do this, and why I never did it in the first place I don't know. I won't mark this resolved though, as my answer doesn't answer this question.
To get around this, I simply return my resultset into a varaible and alter this before returning:
SELECT schema.table.* INTO cached_data
...
IF cached_data.column_name = 'something' THEN
cached_data.column_name = 'something-else';
END IF;
RETURN cached_data;
This works perfectly for my situation.
If you have to use *, specify the table (alias if necessary)
SELECT
t1.*,
CASE
WHEN column_name=1 THEN 'one'
WHEN column_name=2 THEN 'two'
ELSE 'other'
END AS column_name
FROM table t1
This will return all columns from table, plus the new column. If you want to replace that column from table, explicitly state all required columns.
Note: If column_name is already a column in the table, then you will get two columns in the result set with the same name using this approach (HT #Milney)
You can give a nickname to your table and use TABLE_ NICKNAME.* as follow:
SELECT t.*,
CASE id
WHEN 1 THEN 'one'
WHEN 2 THEN 'two'
ELSE 'other'
END AS column_name
FROM your_table t
I have two tables:
Table tablefoo contains a column fulldata.
Table tablebar contains a column partialdata.
I want find a list of tablefoo.fulldata that do NOT have partial matches in tablebar.partialdata.
The following provides a list of tablefoo.fulldata with partial matches in tablebar, but I want the negative of this.
select fulldata from tablefoo
where fulldata like any (select '%' || partialdata from tablebar);
This lists every record in partialdata:
select fulldata from tablefoow
where partialdata not in (select '%' || partialdata from tablebar);
Any idea how to get only the results tablefoo.fulldata that do not contain matches to a leading wildcarded tablebar.partialdata?
I found this link: PostgreSQL 'NOT IN' and subquery which seems like it's headed down the right path, but I'm not getting it to work with the wildcard.
Sure, I could write a script to pull this out of psql and do the comparisons, but it would be much nicer to handle this all as part of the query.
SELECT fulldata
FROM tablefoo f
WHERE NOT EXISTS (
SELECT 1
FROM tablebar b
WHERE f.fulldata LIKE ('%' || b.partialdata)
);
Is there a variable in SQL that can be used to represent ALL the possible values of a field? Something like this pseudo-code
SELECT name FROM table WHERE id = *ALL_EXISTING_ID-s*
I want to return all rows in this case, but later when I do a search and need only one item I can simply replace that variable with the id I'm looking for, i.e.
SELECT name FROM table WHERE id = 1
The simplest way is to remove the WHERE clause. This will return all rows.
SELECT name FROM table
If you want some "magic" value you can use for the ID that you can use in your existing query and it will return all rows, I think you're out of luck.
Though you could use something like this:
SELECT name FROM table WHERE id = IFNULL(?, id)
If the value NULL is provided, all rows will be returned.
If you don't like NULL then try the following query, which will return all rows if the value -1 is provided:
SELECT name FROM table WHERE id = IFNULL(NULLIF(?, -1), id)
Another approach that achieves the same effect (but requires binding the id twice) is:
SELECT name FROM table WHERE (id = ? OR ? = -1)
I am having trouble finding a query.
I have a table 'NotificationExcludes' that contains 1 column 'Name'.
I have a table 'NotificationEvents' that contains columns: Id, Description.
Now I need to select all the NotificationEvents where the description doesn't start with the values contained in 'NotificationExcludes'.
Small example:
NotificationExcludes contains:
Name
The instance was terminated by
NotificationEvents:
ID Description
1 There was a failure on ..
2 The instance was terminated by administrator
Now I need to select everything except if the description starts with a value that is kept in the 'NotificationExcludes'.
I have tried
Select Id, Description
from NotificationEvent
WHERE Description NOT IN (select Name form NotificationExcludes)
But 2 problems with that:
1 The query obviously fails because 'select Name form NotificationExcludes' returns more than 1 record
2 The statement should contain a Like statement where I can use the '%' key. So where description not like 'The instance was terminated by%' can be used somehow
SELECT Id,Description
FROM NotificationEvents ne
WHERE NOT EXISTS(SELECT *
FROM NotificationExcludes nx
WHERE ne.Description
LIKE nx.name + '%') /*<--Might need Concat or || here
dependant upon RDBMS*/
One solution is to JOIN with a LIKE clause on name, appended with %.
SELECT *
FROM NotificationEvents ne
LEFT OUTER JOIN NotificationExcludes nex
ON ne.Description LIKE nex.Name + '%'
WHERE nex.Name IS NULL