I have an SQL query:
select DISTINCT shortname_chn from dim_channel;
The query returns me data for example:
| shortname_chn (VARCHAR) |
|__________________________|
| MTV |
| National Geographic|
| Discovery |
| ARY News |
How can I manipulate the SQL query so that I can add an additional row to the returned rows.
Following is the result I wish to get after running some query:
| shortname_chn (VARCHAR) |
|__________________________|
| MTV |
| National Geographic|
| Discovery |
| ARY News |
| ALL |
Where the last row "ALL" is user defined, not present in the database.
In the above mentioned regard, I researched and came across this question : How to add a user defined column with a single value to a SQL query but it targets the problem of adding a whole new column.
select DISTINCT shortname_chn from dim_channel
UNION
SELECT 'ALL'
You can simply do something like this by UNIONing with a query that returns your fake row, e.g.:
SELECT DISTINCT
shortname_chn
FROM dim_channel
UNION ALL
SELECT 'ALL' AS shortname_chn
Related
I have a table where it has two columns, the first column has the stores names and the second column has the products names.
Each store has multiple products, and multiple stores can share the same product.
How can I Run READ only commands against this table so I get a distinct list of Stores and then query a list of products in each Store?
PS; I don't want to run any write operations in my sql db.
The end result should be something like:
----------------------
| Store | Product |
----------------------
| Store1| Product1 |
| Store1| Product2 |
| .. | .. |
| Store2| Product1 |
| Store2| Product2 |
| .. | .. |
| Store3| Product1 |
| Store3| Product2 |
| .. | .. |
----------------------
The question was already Answered below, Here is the query that worked:
SELECT DISTINCT product,store
FROM table_name
WHERE store in (
SELECT DISTINCT store
FROM table_name
);
I can't understand the nature of the result you want, but i imagine that you want a list of prodects per store. in that case you can use this requets
SELECT * FROM table_name WHERE store in (SELECT DISTINCT store from table_name);
Table name : Students.
The Table i have:
mysql> SELECT * from Students;
+-----------+-------------+-------+
| Rollno | Name | Marks |
+-----------+-------------+-------+
| 251602122 | Sumit Tyagi | 70 |
| 251602121 | parveen | 90 |
+-----------+-------------+-------+
Following query returns the following result even 8 is not a attribute.
mysql> select 8 from Students;
+---+
| 8 |
+---+
| 8 |
| 8 |
+---+
Similarly
mysql> SELECT 'some_string' from Students;
+-------------+
| some_string |
+-------------+
| some_string |
| some_string |
I just want to know why this happens.
The query returns one line for every record in your table.
But you don't select data from those record. You just select the number 8 for each line. And this gets returned.
Select statement looks for column name in a table. You can make sure SQL look for a column name in a table by using TableName.ColumnName.
In the example you wrote, you are asking for a constant or hardcoded value 8/some_string to be returned from the table which is not the column name. So it will return the hardcoded or constant value you asked for, the number of times equal to number of rows in your table.
If you want to make sure it look for the column name, use the syntax I mentioned as TableName.ColumnName. You can also provide an alias for your table. So in the example above, if you use the syntax as
SELECT Students.8 from Students;
or
SELECT s.8 FROM Students s;
It will look for column name as 8 instead of constant or hardcoded value 8.
If I am not wrong, it is a best practice to use TableName.ColumnName or alias.ColumnName while writing queries as it checks for column name in that particular table.
Here's a simplified version of my troubles. 3 tables, the first (transit) will be used in upcoming procedures and functions, the second (products) will hold stationary data about products, the third (userWatchList) will hold user-specific data related to products.
TABLE: transit
+---------+------+
| ranking | data |
+---------+------+
| | |
+---------+------+
TABLE: products
+----+------+-----------------+
| ID | data | importantnumber |
+----+------+-----------------+
| 1 | c | 10 |
| 2 | u | 20 |
| 3 | t | 20 |
| 4 | u | 40 |
+----+------+-----------------+
TABLE: userWatchList
+---------+----+
| ranking | ID |
+---------+----+
| 1 | 2 |
| 2 | 1 |
| 3 | 4 |
| 4 | 3 |
+---------+----+
I need to insert into "transit" the data and ranking of rows that are within the needed ranking range and the data of which meets certain requirements.
I now want the ranking and data of a product, that has an importantnumber value of 20.
Say the allowed ranking range was between 1 and 2, SELECT * FROM transit at the end of the desired process would output:
+---------+------+
| ranking | data |
+---------+------+
| 1 | 'u' |
+---------+------+
Say the allowed ranking range was between 1 and 3, SELECT * FROM transit at the end of the desired process would output:
+---------+------+
| ranking | data |
+---------+------+
| 1 | 'u' |
| 4 | 't' |
+---------+------+
My vision of a possible solution...
To make sure the ranking falls within the needed range, I thought I might use dynamic SQL:
SET #IDsRetrieveStmt = CONCAT("SELECT group_concat(ID SEPARATOR ',') INTO #IDsStr FROM userWatchList WHERE ranking BETWEEN ', #rankingmin,' AND ', #rankingmax,';');
PREPARE stmt FROM #IDsRetrieveStmt;
EXECUTE stmt;
Now. To add ranking value to those fields... what should i do? I imagine one option is somewhere along the lines of:
SET #fetch_data_stmt = CONCAT('INSERT INTO transit (data, ranking) SELECT data, ( **** ) FROM products WHERE ID IN ( ', #IDsStr, ') AND importantnumber=20;');
PREPARE stmt FROM #fetch_data_stmt;
EXECUTE stmt;
** some unknown magic here that fetches ranking from a row with the same ID from 'products' table. This could be SELECT ranking FROM userWatchList WHERE ID=ID, but as you see, the ID part will probably create a conflict. Also, it seems a bit ineffective to run a new SELECT query with every inserted row.
I am sure there is a more effective way of doing this that I haven't heard of yet.
What's the best way of achieving this? Thanks in advance!
The first, and most important, part of the answer is the query that generates the data you want. You need to join the two tables together and use your criteria as conditions in the query:
select ranking, data
from userWatchList u
join product p on p.ID = u.ID
where ranking between ? and ?
and importantnumber = ?
Of course substituting ? with your criteria.
The next part of the answer is more advice. Unless there's an extremely compelling reason to do so, don't create a table to hold the data output from this query, because it's derived data that is out of date the instant it's created, unless you put in complicated database infrastructure (triggers) to keep it fresh.
Instead, create a view, that's like a table to a client (an application), but is actually a query under the hood:
create view transit as
select ranking, data, importantnumber
from userWatchList u
join product p on p.ID = u.ID
Then to use:
select ranking, data
from transit
where ranking between ? and ?
and importantnumber = ?
How to extract and get the value of records of a column in a table.
The 'student' table has a column as 'user_ID'. Here are some records of it.
---------------------
| user_ID |
---------------------
| MPhil/FT/2011/021 |
| MPhil/PT/2013/023 |
| MPhil/PT/2012/029 |
| MPhil/FT/2010/035 |
---------------------
After 'MPhil/FT' or 'MPhil/PT' the year is given. How to write the SQL query to get the year of user_ID? (Like 2011,2013 etc)
You may try to use the SUBSTRING() & SUBSTRING_INDEX() that are available in MySQL.
Or may be you can simple use
select LEFT(Right(user_ID,8),4)
I've got a table in MySQL that looks roughly like:
value | count
-------------
Fred | 7
FRED | 1
Roger | 3
roger | 1
That is, it was created with string ops outside of MySQL, so the values are case- and trailing-whitespace-sensitive.
I want it to look like:
value | count
-------------
Fred | 8
Roger | 4
That is, managed by MySQL, with value a primary key. It's not important which one (of "Fred" or "FRED") is kept.
I know how to do this in code. I also know how to generate a list of problem values (with a self-join). But I'd like to come up with a SQL update/delete to migrate my table, and I can't think of anything.
If I knew that no pair of records had variants of one value, with the same count (like ("Fred",4) and ("FRED",4)), then I think I can do it with a self-join to copy the counts, and then an update to remove the zeros. But I have no such guarantee.
Is there something simple I'm missing, or is this one of those cases where you just write a short function outside of the database?
Thanks!
As an example of how to obtain the results you are looking for with a SQL query alone:
SELECT UPPER(value) AS name, SUM(count) AS qty FROM table GROUP BY name;
If you make a new table to hold the correct values, you INSERT the above query to populate the new table as so:
INSERT INTO newtable (SELECT UPPER(value) AS name, SUM(count) AS qty FROM table GROUP BY name);
Strangely, MySQL seems to do this for you. I just tested this in MySQL 5.1.47:
create table c (value varchar(10), count int);
insert into c values ('Fred',7), ('FRED',1), ('Roger',3), ('roger',1);
select * from c;
+-------+-------+
| value | count |
+-------+-------+
| Fred | 7 |
| FRED | 1 |
| Roger | 3 |
| roger | 1 |
+-------+-------+
select value, sum(count) from c group by value;
+-------+------------+
| value | sum(count) |
+-------+------------+
| Fred | 8 |
| Roger | 4 |
+-------+------------+
I was surprised to see MySQL transform the strings like that, and I'm not sure I can explain why it did that. I was expecting to have to get four distinct rows, and to have to use some string functions to map the values to a canonical form.