Is it possible to use the names of the actual columns for the order by clause?
I am using a view to let a client use a reporter writer (Pentaho) and this would make things easier on them.
To clarify, I want to put the results in alphabetical order of the column names themselves. I want to sort the data using the columns, not the data IN the columns.
In PostgreSQL you can try:
SELECT column_name, data_type FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME =
'my_table' ORDER BY column_name;
If what you mean is to change the order of the columns themselves according to their names (that would make sense only if you are using SELECT *, I guess), I'm afraid that's not possible, at least not straightforwardly. And that sounds very unSQL, I'd say...
Sure, you can order by column name, column alias, or column position:
select a, b from table order by b;
select a as x, b as y from table order by x, y;
select a, b from table order by 1;
You can create the view with the columns in any order you like. Then SELECT * FROM your_view queries will return the columns in the order specified by the view.
Related
I have a dynamic sql, where I need to select two columns(say A & B) from the table. I need to generate the result set only if column B has at least one non zero value. If there is no non zero value in the column B, result set should be empty.
Should be that simple, just as you wrote the rule -
select a, b
from the_table
where exists (select from the_table where b <> 0);
I am trying for hours to transpose one table into another one this way:
My idea is to grab on an expression (which can be a simple SELECT * FROM X INNER JOIN Y ...), and transpose it into a MATERIALIZED VIEW.
The problem is that the original table can have an arbitrary number of rows (hence columns in the transposed table). So I was not able to find a working solution, not even with colpivot.
Can this ever be done?
Use conditional aggregation:
select "user",
max(value) filter (where property = 'Name') as name,
max(value) filter (where property = 'Age') as age,
max(value) filter (where property = 'Address') as addres
from the_table
group by "user";
A fundamental restriction of SQL is, that all columns of a query must be known to the database before it starts running that query.
There is no way you can have a "dynamic" number of columns (evaluated at runtime) in SQL.
Another alternative is to aggregate everything into a JSON value:
select "user",
jsonb_object_agg(property, value) as properties
from the_table
group by "user";
Is it possible to SELECT * but without n-th column, for example 2nd?
I have some view that have 4 and 5 columns (each has different column names, except for the 2nd column), but I do not want to show the second column.
SELECT * -- how to prevent 2nd column to be selected?
FROM view4
WHERE col2 = 'foo';
SELECT * -- how to prevent 2nd column to be selected?
FROM view5
WHERE col2 = 'foo';
without having to list all the columns (since they all have different column name).
The real answer is that you just can not practically (See LINK). This has been a requested feature for decades and the developers refuse to implement it. The best practice is to mention the column names instead of *. Using * in itself a source of performance penalties though.
However, in case you really need to use it, you might need to select the columns directly from the schema -> check LINK. Or as the below example using two PostgreSQL built-in functions: ARRAY and ARRAY_TO_STRING. The first one transforms a query result into an array, and the second one concatenates array components into a string. List components separator can be specified with the second parameter of the ARRAY_TO_STRING function;
SELECT 'SELECT ' ||
ARRAY_TO_STRING(ARRAY(SELECT COLUMN_NAME::VARCHAR(50)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME='view4' AND
COLUMN_NAME NOT IN ('col2')
ORDER BY ORDINAL_POSITION
), ', ') || ' FROM view4';
where strings are concatenated with the standard operator ||. The COLUMN_NAME data type is information_schema.sql_identifier. This data type requires explicit conversion to CHAR/VARCHAR data type.
But that is not recommended as well, What if you add more columns in the long run but they are not necessarily required for that query?
You would start pulling more column than you need.
What if the select is part of an insert as in
Insert into tableA (col1, col2, col3.. coln) Select everything but 2 columns FROM tableB
The column match will be wrong and your insert will fail.
It's possible but I still recommend writing every needed column for every select written even if nearly every column is required.
Conclusion:
Since you are already using a VIEW, the simplest and most reliable way is to alter you view and mention the column names, excluding your 2nd column..
-- my table with 2 rows and 4 columns
DROP TABLE IF EXISTS t_target_table;
CREATE TEMP TABLE t_target_table as
SELECT 1 as id, 1 as v1 ,2 as v2,3 as v3,4 as v4
UNION ALL
SELECT 2 as id, 5 as v1 ,-6 as v2,7 as v3,8 as v4
;
-- my computation and stuff that i have to messure, any logic could be done here !
DROP TABLE IF EXISTS t_processing;
CREATE TEMP TABLE t_processing as
SELECT *, md5(t_target_table::text) as row_hash, case when v2 < 0 THEN true else false end as has_negative_value_in_v2
FROM t_target_table
;
-- now we want to insert that stuff into the t_target_table
-- this is standard
-- INSERT INTO t_target_table (id, v1, v2, v3, v4) SELECT id, v1, v2, v3, v4 FROM t_processing;
-- this is andvanced ;-)
INSERT INTO t_target_table
-- the following row select only the columns that are pressent in the target table, and ignore the others.
SELECT r.* FROM (SELECT to_jsonb(t_processing) as d FROM t_processing) t JOIN LATERAL jsonb_populate_record(NULL::t_target_table, d) as r ON TRUE
;
-- WARNING : you need a object that represent the target structure, an exclusion of a single column is not possible
For columns col1, col2, col3 and col4 you will need to request
SELECT col1, col3, col4 FROM...
to omit the second column. Requesting
SELECT *
will get you all the columns
I have the following schema dataset which i want to transform into a table that can be exported to SQL. I am using HIVE. Input as follows
call_id,stat1,stat2,stat3
1,a,b,c,
2,x,y,z,
3,d,e,f,
1,j,k,l,
The output table needs to have call_id as its primary key so it needs to be unique. The output schema should be
call_id,stat2,stat3,
1,b,c, or (1,k,l)
2,y,z,
3,e,f,
The problem is that when i use the keyword DISTINCT in the HIVE query, the DISTINCT applies to the all the colums combined. I want to apply the DISTINCT operation only to the call_id. Something on the lines of
SELECT DISTINCT(call_id), stat2,stat3 from intable;
However this is not valid in HIVE(I am not well-versed in SQL either).
The only legal query seems to be
SELECT DISTINCT call_id, stat2,stat3 from intable;
But this returns multiple rows with same call_id as the other columns are different and the row on the whole is distinct.
NOTE: There is no arithmetic relation between a,b,c,x,y,z, etc. So any trick of averaging or summing is not viable.
Any ideas how i can do this?
One quick idea,not the best one, but will do the work-
hive>create table temp1(a int,b string);
hive>insert overwrite table temp1
select call_id,max(concat(stat1,'|',stat2,'|',stat3)) from intable group by call_id;
hive>insert overwrite table intable
select a,split(b,'|')[0],split(b,'|')[1],split(b,'|')[2] from temp1;
,,I want to apply the DISTINCT operation only to the call_id"
But how will then Hive know which row to eliminate?
Without knowing the amount of data / size of the stat fields you have, the following query can the job:
select distinct i1.call_id, i1.stat2, i1.stat3 from (
select call_id, MIN(concat(stat1, stat2, stat3)) as smin
from intable group by call_id
) i2 join intable i1 on i1.call_id = i2.call_id
AND concat(i1.stat1, i1.stat2, i1.stat3) = i2.smin;
I have the need to look at two tables that share two variables and get a list of the data from one table that does not have matching data in the other table. Example:
Table A
xName
Date
Place
xAmount
Table B
yName
Date
Place
yAmount
I need to be able to write a query that will check Table A and find entries that have no corresponding entry in Table B. If it was a one variable issue I could use not in statement but I can't think of a way to do that with two variables. A left join also does not appear like you could do it. Since looking at it by a specific date or place name would not work since we are talking about thousands of dates and hundreds of place names.
Thanks in advance to anyone who can help out.
SELECT TableA.Date,
TableA.Place,
TableA.xName,
TableA.xAmount,
TableB.yName,
TableB.yAmount
FROM TableA
LEFT OUTER JOIN TableB
ON TableA.Date = TableB.Date
AND TableA.Place = TableB.Place
WHERE TableB.yName IS NULL
OR TableB.yAmount IS NULL
SELECT * FROM A WHERE NOT EXISTS
(SELECT 1 FROM B
WHERE A.xName = B.yName AND A.Date = B.Date AND A.Place = B.Place AND A.xAmount = B.yAmount)
in ORACLE:
select xName , xAmount from tableA
MINUS
select yName , yAmount from tableB