I can’t find how to rename the row counting column in a table in an SQL Server RDMS. When you create a table and you have user created columns, A and B for example, to the farthest right of those columns, you have the Row Number column.
It does not have a title. It just sequentially counts all the rows in your table. It's default. Is it possible to manipulate this column denoting the row numbers? Meaning, can I rename it, put its contents in descending order, etc. If so, how?
And if not, what are the alternatives to have a sequentially counting column counting all the rows in my table?
No. You can create your own column with sequential values using an identity column. This is usually a primary key.
Alternatively, when you query the table, you can assign a sequential number (with no gaps) using row_number(). In general, you want a column that specifies the ordering:
select t.*, row_number() over (order by <ordering column>) as my_sequential_column
from t;
Related
Given the following file (that I have no control over):
I want to be able to select the last row. I tried doing an ORDER BY the date column; however, as you can see there may be multiple date columns.
Without an ID field, how can I select the last column that physically exists in the file?
I've spent a while googling everything points to sorting by a column.
As you have no clustered index (which would constitute the physical ordering of the data), it is impossible. Tables are only ordered deterministically if you use an order by clause.
See e.g. sql-best-practice-to-deal-with-default-sort-order
If your current concern could still be considered in the database schema design, the adding of a loaddate field can be considered, which would be set to the time the row is created. (If your last column is such a loaddate you could still use an order by clause on the column)
I am Omar, a new learner of SQL.
I have a large excel sheet that I want to analyze by SQL.
It has the following columns (Manufacturers, Products, sales)
the problem is, in the first column 'Manufacturers,' the manufacturer name has only been entered once per one manufacturer. while for the rest of the below rows, the cells are empty until the next manufacturer.
Please refer to the attached image for more understanding.
How can I remove these null values in my query results while keeping the values of the product column value?
thank you
The main problem you have is that SQL tables represent unordered sets. So, if you have only your specified columns, you cannot reconstruct the Excel format.
To solve this, you want to load the data into a table that has an identity or auto-incremented column, in order to preserve the insertion order. The exact details depend on the database. Let me call this column id.
Then you can "spread" the value where it is missing. One method is:
select t.*,
max(manufacturer) over (partition by manufacturer_grp) as imputed_manufacturer
from (select t.*,
count(manufacturer) over (order by id) as manufacturer_grp
from t
) t
How do I insert a row between here?
Data is not intended to be stored SQL tables in any particular order, so it's not appropriate to insert a row at a particular position. You use an SQL SELECT query to extract the data you want and ORDER BY to specify how it is sorted. If you really want to have this row in a particular position, add an ID column as the primary key and number the ID column values in the sequence that you want. Whatever you are using to view your rows will order them by the ID column by default. However, you're going to experience this same problem every time you want to add a new row as SQL tables are not intended to be used in this way.
I work on Presto SQL tables that don't have unique row identifiers. The only way to identify a specific record is to query all of its fields.
Is there in Presto some kind of hidden field, say ROW_PRIMARY_KEY, that would allow me to uniquely identify records in my tables?
Short of a primary key, you could just toss in a
ROW_NUMBER() OVER (PARTITION BY some, columns ORDER BY some_other_column) as rn
This will define a row number where some, columns would be a psuedo-primary key.
To extend and simplify the answer by JNevill, if you just want a row number:
SELECT row_number() OVER () AS row_num
Note that OVER () may function the same as OVER (PARTITION BY 1), implying that all rows are assigned to the same partition. In this way, all rows will have unique row numbers.
I have a SQLite table sorted by column ID. But I need to sort it by another numerical field called RunTime.
CREATE TABLE Pass_2 AS
SELECT RunTime, PosLevel, PosX, PosY, Speed, ID
FROM Pass_1
The table Pass_2 looks good, but I need to renumber the ID column from 1 .. n without resorting the records.
It is a principle of SQL databases that the underlying tables have no natural or guaranteed order to their records. You must specify the order in which you want to see the records when SELECTing from a table using an ORDER BY clause.
You can obtain the records you want using SELECT * FROM your_table ORDER BY RunTime, and that is the correct and reliable way to do this in any SQL database.
If you want to attempt to get the records in Pass_2 to "be" in RunTime order, you can add the ORDER BY clause to the SELECT you use to create the table but remember: you are not guaranteed to get the records back in the order in which they were added to the table.
When might you get the records back in a different order? This is most likely to happen when your query can be answered using columns in a covering index -- in that case the records are more likely to be returned in index order than any "natural" order (but again, no guarantees with an ORDER BY clause).
If you want a new ID column starting at 1, then use the ROW_NUMBER() function. Instead of ID in your query use this ROW_NUMBER() OVER(ORDER BY Runtime) AS ID.... This will replace the old ID column with a freshly calculated column