There are three columns of date information (month, day, year) in a table and I would like to create a new column in the table and combine those 3 columns into a the new column so that I can have a single formatted date. How can I do this? I know how to query this but I am trying to figure out how to copy this information to the original table. Thanks in advance.
If I understood well, you need to alter your table and add a datetime column
You need to do something like this
UPDATE YourTable
SET DATECOLUMN = '#' & DAYCOLUMN & '/' & MONTHCOLUMN & '/' & YEARCOLUMN & '#'
It was the sintaxis in access if i remember it well.
Greetings.
There are a number of way of managing such a data scrubbing exercise e.g.
CREATE a new table including a new NOT NULL column and omitting the now-redundant columns, INSERT..SELECT into the new table only the data you require, DROP the old table (you'll end up with a different table name which may not be a bad thing).
ADD a new nullable column to the existing table (or NOT NULL if you have an appropriate DEFAULT), UPDATE the new column, alter the column to make it NOT NULL then DROP the now-redundant columns.
Related
I am writing the following query to add a column at a specified position but getting the below error:
alter table quantum_raw_dev.rpt_backup_allocation
change upt_type upt_type STRING after tray_size;
You can add one or more columns to the end of the column list using:
ALTER TABLE <table_name> ADD COLUMNS (col_name col_type, ...);
[note: there is NO comma between column name and type]
Adding or Removing Columns
You can add one or more columns to the end of the column list using ADD COLUMNS,
or (with Impala only) you can delete columns using DROP COLUMN.
The general syntax is
ALTER TABLE tablename ADD COLUMNS (col1 TYPE1,col2 TYPE2,… );
ALTER TABLE tablename DROP COLUMN colname;
For example, you can add a bonus integer column to the employees table:
ALTER TABLE employees ADD COLUMNS (bonus INT);
Or you can drop the office_id column from the employees table:
ALTER TABLE employees DROP COLUMN office_id;
Notes
DROP COLUMN is not available in Hive, only in Impala. However, see “Replacing All Columns” below.
You can only drop one column at a time.
To drop multiple columns, use multiple statements or use the method to replace columns (see below).
You cannot add a column in the middle of the list rather than at the end.
You can, however, add the column then change the order (see above) or use the method to replace columns (see below).
As with changing the column order, these do not change the data files.
If the table definition agrees with the data files before you drop any column other than the last one,
you will need to recreate the data files without the dropped column's values.
If you drop the last column, the data will still exist but it will be ignored when a query is issued.
If you add columns for which no data exists, those columns will be NULL in each row.
Replacing All Columns
You can also completely replace all the columns with a new column list.
This is helpful for dropping multiple columns,
<h1>or if you need to add columns in the middle of the list<h1>
<h2>(like your use case)<h2>
The general syntax is
ALTER TABLE tablename REPLACE COLUMNS (col1 TYPE1,col2 TYPE2,… );
This completely removes the existing list of columns and replaces it with the new list.
Only the columns you specify in the ALTER TABLE statement will exist, and they will be in the order you provide.
Note
Again, this does not change the data files, only the metadata for the table,
so you'll either want the new list to match the data files or need to recreate the data files to match the new list.
I do not think you can add columns in between columns in Impala like above.
You can backup the data, drop the and recreate with new structure, and load the table from backup. Also if you have HIVE in your system you can try to do below steps -
Add column first and then use below commands to move columns around.
ALTER TABLE tab ADD COLUMNS (id BIGINT);
This moves id column to the beginning.
ALTER TABLE tab CHANGE COLUMN id id BIGINT first;
This moves existing_col after id.
ALTER TABLE tab CHANGE COLUMN existing_col existing_col string AFTER id;
Please refresh/invalidate metadata after applying all DDLs.
You cannot add column in between. Best way is to archive the data in another table. Drop the impala old table and create a fresh table with new columns as per the desired location and then reinsert the data.
I have a "source data" table with columns A,B,C,D,E,F
I use this table to populate a live table by using
INSERT INTO LIVETABLE
SELECT *
FROM SOURCEDATATABLE
Recently, a new column (C1) was added to the LIVETABLE
All I want to do is insert a C1 column into my SOURCEDATATABLE between C and D so that it now is A,B,C,C1,D,E,F. There is no need to populate with data as the LIVETABLE accepts NULLs
Is there any easy solution?
EDIT - MISSING INFORMATION
This table is one of many and my approach to using the INSERT INTO is due to having to use dynamic SQL (for various other reasons) so I cannot specify the column names
There is a reason for the Mantra "I shall not use SELECT *" and you ran straight into it. Add the column to SOURCEDATATABLE (if necessary) and enumerate the columns in the SELECT clause using NULL for the new one.
The only way to insert a new column between two columns is to create a new table with the columns in the order you want, copy the data into it, drop the old table and rename the new table with the old name. Make sure you remove primary key identities to maintain the identity column.
I have a sql table that I am trying to add a column from another table to. Only when I execute the alter table query it does not pull the values out of the table to match the column where I am trying to make the connection.
For example I have column A from table 1 and column A from table 2, they are supposed to coincide. ColumnATable1 being an identification number and ColumnATable2 being the description.
I tried this but got an error...
alter table dbo.CommittedTbl
add V_VendorName nvarchar(200)
where v_venkey = v_vendorno
It tells me that I have incorrect syntax... Anyone know how to accomplish this?
alter table dbo.CommittedTbl
add V_VendorName nvarchar(200);
go
update c
set c.V_VendorName = a.V_VendorName
from CommittedTbl c
join TableA a
on c.v_venkey = a.v_vendorno;
go
I'm just guessing at your structure here.
alter table 2 add column A <some_type>;
update table2 set column A = (select column_A from table2 where v_venkey = v_vendorno);
Your names for tables and columns are a bit confusing but I think that should do it.
There is no WHERE clause for an ALTER TABLE statement. You will need to add the column (your first two lines), and then insert rows based upon a relationship you define between the two tables.
ALTER TABLE syntax:
http://msdn.microsoft.com/en-us/library/ms190273%28v=sql.90%29.aspx
There are several languages within SQL:
DDL: Data Definition Language - this defines the schema (the structure of tables, columns, data types) - adding a column to a table affects the table definitions and all rows will have that new column (not just some rows according to a criteria)
DML: Data Manipulation Language - this affects data within a table, and inserting, updating or other changes fall into this and you can update some data according to criteria (and this is where a WHERE clause would come in)
ALTER is a DDL statement, while INSERT and UPDATE are DML statements.
The two cannot really be mixed as you are doing.
You should ALTER your table to add the column, then INSERT or UPDATE the column to include appropriate data.
Is it possible that you want a JOIN query instead? If you want to join two tables or parts of two tables you should use JOIN.
have a look at this for a start if you need to know more LINK
hope that helps!
Is there an SQL command on the AS400/iSeries/System-i/whatever to add a column to a table in a specific ordinal position, or moving an existing column to a different position?
IBM i 7.1 now allows you to add a column in front of another.
ALTER TABLE table ADD COLUMN colname ... BEFORE othercolumn
No. The ALTER TABLE statement will allow you add a column to a table, but, according to the documentation:
The new column is the last column of the table; that is, if initially there are n columns, the added column is column n+1.
If you'd like to change the order of columns in your table, your best bet is to:
Use the RENAME statement to rename the table.
Recreate the table, with its original name, with the columns in the order that you want.
Use an INSERT SELECT to populate the new table with the data from the renamed table.
When you're sure the data is intact, you can drop the renamed version of the table.
I need a fast way duplicate a DATETIME column in a table and give it a new name.
I have a column named myDate in my table called myResults, I need a query to make a new column in the table called newDate which has the exact same data as the myDate column.
Is there a faster way to do this than by doing the obvious 2 step approach of make a new column, and then copying all the data (it's a large table and I'm looking for the fastest approach)?
Obvious solution:
ALTER TABLE `myResults` ADD `newDate` DATETIME;
UPDATE `myResults` SET `newDate` = `myDate`;
UPDATE `table_name` SET `new_column` = `existing_column` WHERE `id`=`id`
The obvious solution is the only solution, unfortunately.
However note that in general you shouldn't be copying a column in relational databases.
If you just need a default in there, you can either choose what the default is statically or use a function call.
ALTER TABLE `myResults` ADD `newDate` DATETIME DEFAULT '2010-01-01';
or
ALTER TABLE `myResults` ADD `newDate` DATETIME DEFAULT current_timestamp;
Why would your workload ever demand a new datetime column, that duplicates another columns data? This sounds like horrable practice? How about telling us what you're trying to achieve? You can pull a second column with the same data in a few different ways, without actually duplicating the data:
SELECT date1 AS date_old, date1 AS date_new FROM table;
-or-, you can create a view
CREATE VIEW virtual_table AS
SELECT date1 AS date_old, date1 AS date_new FROM table
;
SELECT * FROM virtual_table;