How to get a unique, identical value of a table?
For example, if there are tables like 't_aa', 't_bb', 't_cc', I want a result like below.
id | table_name
-------------------
1 | 't_aa'
2 | 't_bb'
3 | 't_cc'
What I exactly want is to get a specific, and unique number from the name of tables.
I have tried
SELECT * FROM information_schema.tables;
-- or
SELECT * FROM pg_catalog.pg_tables;
but this doesn't provide any identical numbers to me.
I hope there is some way to get results like above by using some lines of query,
but if I really have to make a new table for this, that could be okay as an alternative.
please help me, thank you
-- edit
I need numbers because I will use it as an advisory lock key for some reasons.
ThIs is it:
SELECT table_name,ROW_NUMBER () OVER (
ORDER BY table_name
) as id FROM information_schema.tables;
Related
Suppose there is a table which has several identical rows. I can copy the distinct values by
SELECT DISTINCT * INTO DESTINATIONTABLE FROM SOURCETABLE
but if the table has a column named value and for the sake of simplicity its value is 1 for one particular item in that table. Now that row has another 9 duplicates. So the summation of the value column for that particular item is 10. Now I want to remove the 9 duplicates(or copy the distinct value as I mentioned) and for that item now the value should show 10 and not 1. How can this be achieved?
item| value
----+----------------
A | 1
A | 1
A | 1
A | 1
B | 1
B | 1
I want to show this as below
item| value
----+----------------
A | 4
B | 2
Thanks in advance
You can try to use SUM and group by
SELECT item,SUM(value) value
FROM T
GROUP BY item
SQLfiddle:http://sqlfiddle.com/#!18/fac26/1
[Results]:
| item | value |
|------|-------|
| A | 4 |
| B | 2 |
Broadly speaking, you can just us a sum and a GROUP BY clause.
Something like:
SELECT column1, SUM(column2) AS Count
FROM SOURCETABLE
GROUP BY column1
Here it is in action: Sum + Group By
Since your table probably isn't just two columns of data, here is a slightly more complex example showing how to do this to a larger table: SQL Fiddle
Note that I've selected my rows individually so that I can access the necessary data, rather than using
SELECT *
And I have achieved this result without the need for selecting data into another table.
EDIT 2:
Further to your comments, it sounds like you want to alter the actual data in your table rather than just querying it. There may be a more elegant way to do this, but a simple way use the above query to populate a temporary table, delete the contents of the existing table, then move all the data back. To do this in my existing example:
WITH MyQuery AS (
SELECT name, type, colour, price, SUM(number) AS number
FROM MyTable
GROUP BY name, type, colour, price
)
SELECT * INTO MyTable2 FROM MyQuery;
DELETE FROM MyTable;
INSERT INTO MyTable(name, type, colour, price, number)
SELECT * FROM MyTable2;
DROP TABLE MyTable2;
WARNING: If youre going to try this, please use a development environment first (i.e one you don't mind breaking!) to ensure it does exactly what you want it to do. It's imperative that your initial query captures ALL the data you want.
Here is the SQL Fiddle of this example in action: SQL Fiddle
I have the follwing given two tables which can not be changed.
1: DataTypes
+----------------------+-----------------------+
| datatypename(String) | datatypetable(String) |
+----------------------+-----------------------+
Example data:
+-----------+------------+
| CycleTime | datalong |
+-----------+------------+
| InjTime1 | datadouble |
+-----------+------------+
2: datalong_1 (data model does not matter here)
I want to make a query now that reads the datatypetable attribute from the datatypes table, adds the String "_1" to it and selects all content from it.
I imagined it, from a programmatic perspective, to look something similar to this statement which obviously doesn't work yet:
SELECT * FROM
(SELECT datatypetable FROM datatypes WHERE datatypename = 'CycleTime') + '_1'
How can I make this happen in SQL using HSQLDB?
Thanks to Leonidas199x I know now how to get in the '_1' in but how do I tell the FROM statement that the subselect is not a new table I want to read from but instead the name of an existing table I want to read from.
SELECT * FROM
(SELECT RTRIM(datatypetable)+'_1' FROM datatypes WHERE datatypename = 'CycleTime')
According to this question which is identical to mine this is not possible:
using subquery instead of the tablename
:(
Can you explain your data model in a little more detail? I am not sure I understand exactly what it is you are looking to do.
If you are wanting to add _1 to the 'datatypename', you can use:
SELECT datatypename+'_1'
FROM datatypes
Using Oracle 10G
Say for example I have a table with three fields in it, I'd like one query which selects the counts of each column where they are not null. Field name
----------------------------------
| strTest1 | strTest2 | strTest3 |
----------------------------------
I know how to get the count of each one individually:
select count(*) from tablename where strTest1 is not null
but I'd like to know if it's possible to do this within one query for all 3 fields.
Thanks
It sounds like you want:
SELECT COUNT(STRTEST1), COUNT(STRTEST2), COUNT(STRTEST3) FROM YOUR_TABLE
This is staight forward I believe:
I have a table with 30,000 rows. When I SELECT DISTINCT 'location' FROM myTable it returns 21,000 rows, about what I'd expect, but it only returns that one column.
What I want is to move those to a new table, but the whole row for each match.
My best guess is something like SELECT * from (SELECT DISTINCT 'location' FROM myTable) or something like that, but it says I have a vague syntax error.
Is there a good way to grab the rest of each DISTINCT row and move it to a new table all in one go?
SELECT * FROM myTable GROUP BY `location`
or if you want to move to another table
CREATE TABLE foo AS SELECT * FROM myTable GROUP BY `location`
Distinct means for the entire row returned. So you can simply use
SELECT DISTINCT * FROM myTable GROUP BY 'location'
Using Distinct on a single column doesn't make a lot of sense. Let's say I have the following simple set
-id- -location-
1 store
2 store
3 home
if there were some sort of query that returned all columns, but just distinct on location, which row would be returned? 1 or 2? Should it just pick one at random? Because of this, DISTINCT works for all columns in the result set returned.
Well, first you need to decide what you really want returned.
The problem is that, presumably, for some of the location values in your table there are different values in the other columns even when the location value is the same:
Location OtherCol StillOtherCol
Place1 1 Fred
Place1 89 Fred
Place1 1 Joe
In that case, which of the three rows do you want to select? When you talk about a DISTINCT Location, you're condensing those three rows of different data into a single row, there's no meaning to moving the original rows from the original table into a new table since those original rows no longer exist in your DISTINCT result set. (If all the other columns are always the same for a given Location, your problem is easier: Just SELECT DISTINCT * FROM YourTable).
If you don't care which values come from the other columns you can use a (bad, IMHO) MySQL extension to SQL and do:
SELECT * FROM YourTable GROUP BY Location
which will give a result set with one row per location and values for the other columns derived from the original data in an undefined fashion.
Multiple rows with identical values in all columns don't have any sense. OK - the question might be a way to correct exactly that situation.
Considering this table, with id being the PK:
kram=# select * from foba;
id | no | name
----+----+---------------
2 | 1 | a
3 | 1 | b
4 | 2 | c
5 | 2 | a,b,c,d,e,f,g
you may extract a sample for every single no (:=location) by grouping over that column, and selecting the row with minimum PK (for example):
SELECT * FROM foba WHERE id IN (SELECT min (id) FROM foba GROUP BY no);
id | no | name
----+----+------
2 | 1 | a
4 | 2 | c
CREATE TABLE `names` ( `name` varchar(20) );
Assume the names table contains all 40 million first names of everyone living in California (for example).
SELECT count(*) as count, name FROM names GROUP BY name ORDER BY name;
How can I optimize this query?
Expected Result:
count | name
9999 | joe
9995 | mike
9990 | kate
.... | ....
2 | kal-el
You have to create an index on the name column of your table. The query is as good as it can be.
Well, what makes you think it's not already optimised? This looks like the sort of query a good database engine should be able to handle relatively easily - particularly if you've got an appropriate index on your table.
Do you actually have a bottleneck here, or are you worrying about something that might happen in the future? If it's the latter, I suggest you try it with your RDBMS (by generating dummy data), and see what happens.