I want to change the column comments on an existing hive table using hive 0.13. This works:
create table test (mycolumn int);
alter table test change mycolumn mycolumn int comment 'hello';
But I can't find a way to do this without repeating the name of the column and the type, both of which are irrelevant to the change. For example:
alter table test change mycolumn comment 'hello'; leads to an error.
If this was for one column it would not be a big deal but I want to do this for large numbers of columns in tables that were not commented. I know this could be done with a script that simply copies the column name and its type but would be nice to know if there were something simpler. Thanks
You can do this using ALTER command.
CREATE TABLE my_table
(id INT COMMENT 'id comment',
name STRING comment 'name comment');
-- change column comment as below.
ALTER TABLE my_table CHANGE id id INT COMMENT 'another comment';
-- see changed column
DESC EXTENDED my_table;
ALTER TABLE test_change CHANGE a1 a1 INT COMMENT 'this is column a1';
Directly its not supported to edit column property for comment the other way around is
alter table dev.travel change num2 clm_num1 int comment 'a new column added';
Now I want to change above one lets do ;
alter table dev.tkt change clm_num1 num2 int comment 'a new column added';
alter table dev.tkt change num2 clm_num1 int comment 'a new column added with new comment';
Related
I have a question related to the conversion of varchar to datetime.
This topic was covered already in the thread
SQL Server Convert Varchar to Datetime
but I would like to advance it bit further.
I have performed BULK INSERT into predefined tables where VARCHAR(255)
is the destination. I have a table dbo.USR_02_ALL_RAW and the field GLTGB which
holds strings in the following format: 07/16/2016.
I can convert it as a single string by the following code:
DECLARE #Date varchar(255)
set #Date= '07/16/2016'
SELECT CONVERT(datetime,RIGHT(#Date,4)+LEFT(#Date,2)+SUBSTRING(#Date,4,2))
and it gives me a result:
2016-07-16 00:00:00.000
However I would like to pass to the code the whole field GLTGB from the table
dbo.USR_02_ALL_RAW, convert it from VARCHAR into DATETIME and update the field GLTGB with these results.(converting the whole field from varchar to datetime)
Thank you!
First clear this, you want to Bulk insert or Bulk update. Since you already have a column GLTGB. If you want to update the value only.
update tab set GLTGB =
CONVERT(datetime,RIGHT(GLTGB,4)+LEFT(GLTGB,2)+SUBSTRING(GLTGB,4,2))
Or
If you want to update the field from varchar to datetime. Then process is little bit lengthy.
Alter table tab add newcol datetime --- Add new datetime type column
update tab set newcol =
CONVERT(datetime,RIGHT(GLTGB,4)+LEFT(GLTGB,2)+SUBSTRING(GLTGB,4,2)) --- update value in new column
Alter table tab drop column GLTGB --- drop GLGTB column
Alter table tab add GLGTB datetime --- add GLGTB column as datetime type
update tab set GLGTB = newcol --- update value from GLGTB from newcol
Alter table tab drop column newcol ---- remove unnecessary newcol
If you convert a value to datetime, then update the same database column it came from with the value then, since that column is still varchar, SQL will have to convert the value back to varchar again in order to store it. So you can't achieve anything useful with that kind of simple approach.
f you want to actually change the data type of the column, and also convert all the values, then I think you need to go through the following process:
1) Create a new varchar column in your table (which will be temporary)
2) copy all the data values from the GLTGB column into the new column (using an UPDATE statement)
3) Drop the GLTGB column
4) Re-create it with the same name but with datetime type
5) Use an UPDATE statement to re-populate the new GLTGB column from your temporary column
6) Finally, drop the temporary column
There may be a simpler way but that seems like the obvious process.
You can use the following code for updating but before that, you need to change the data type of your field to DateTime
update dbo.USR_02_ALL_RAW
set GLTGB=cast(CONVERT(datetime,RIGHT(#Date,4)+LEFT(#Date,2)+SUBSTRING(#Date,4,2)) as datetime)
I added a column using following commands (I used quotation marks so that N is in upper case in my column name)
ALTER TABLE new_table
ADD “Name” VARCHAR(50);
However, I see "nam" column in my table now after running that command.
How can I drop that column?
ALTER TABLE new_table
DROP COLUMN "Name";
I get following error:
ERROR: column "name" of relation "new_table" does not exist
The following statement causes this error:
ALTER TABLE new_table
DROP COLUMN "Name";
seems you are not using double quote " in first query bus some others quotes try suing the same chars “”
ALTER TABLE new_table DROP COLUMN “Name”;
Check how Postgres is storing the column name when you are using a double quote in column name:
select table_name, column_name from information_schema.columns where
table_name='tab1';
Also, you may view the same when you execute a select statement:
select * from table;
Copy the same column name text in your alter statement. Here is the sample column name with both kind of double quotes in PostgreSQL:
create table tab1(data varchar(30));
alter table tab1 ADD “Name1” varchar(50);
alter table tab1 ADD "Name2" varchar(50);
select *from tab1;
select table_name, column_name from information_schema.columns where table_name='tab1';
alter table tab1 drop column “Name1”;
alter table tab1 drop column "Name2";
table_name column_name
tab1 data
tab1 “name1”
tab1 Name2
Here is the link to the fiddle
Note: Avoid using a double quote in the table name, column, etc. In case you use you have to ensure that the same names are specified in all queries.
Edit:
It's simple. If you use "Name" (not same as “Name”, notice quote angle) in the column name then you have to refer the column as "Name". In case “Name” is used then you have to refer by “Name”. The quotes need to match.
Another observation is when "Name" used as column name it makes the column name as Name (N uppercase) as opposed to all lowercase column names by default in the database but needs to be referred as "Name".
I'm new in SQL and I need to create table with specified field format. How to add CHECK condition that will assure that input will be formatted e.g.
[LLLDD]
where L is a letter and D is a digit?
Try this if you are adding the constraint on a new table
CONSTRAINT ck_data_checker CHECK ([columnName] LIKE ('[A-Z][A-Z][A-Z][0-9][0-9]'))
Try this if you are adding the constraint on existing table
ALTER TABLE tableName
ADD CONSTRAINT ck_data_checker CHECK ([columnName] LIKE ('[A-Z][A-Z][A-Z][0-9][0-9]'))
Try this: http://sqlfiddle.com/#!6/3974b
create table test (
field1 char(5),
check (field1 like '[a-z][a-z][a-z][0-9][0-9]')
);
insert into test values ('ttt09'); --this will succeed
If you were to change the insert to:
insert into test values ('testi'); -- this will fail
insert into test values ('12345'); -- this will fail
I'm no sql server expert, but I think you can add a LIKE with a regular expression. Have a look at these websites
https://msdn.microsoft.com/en-us/library/ms179859.aspx
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/dc127433-2982-4065-b290-f411a075a694/use-regular-expressions-to-check-sql-server-2012-table-fields?forum=databasedesign
I am using Apache derby database v 10.9.1.0. There is one existing table Country-having column LawID of type bigint. It contains records having integer data only. Due to some business reason, I need to alter its data type from 'bigint' to 'varchar' . I tried following two ways to alter existing table. But both ways did not work.
a. first way
ALTER TABLE Country ADD COLUMN LawID_NEW VARCHAR(50);
UPDATE Country SET LawID_NEW = LawID;
ALTER TABLE Country DROP COLUMN LawID;
RENAME COLUMN Country.LawID_NEW TO LawID;
It shows message like :Columns of type 'VARCHAR' cannot hold values of type 'BIGINT'.
b. second way
ALTER TABLE Country ALTER LawID SET DATA TYPE VARCHAR(50);
It shows error message like : Invalid type specified for column 'LawID'. The type of a column may not be changed.
Any help related to correct alter query is highly appreciated, Thanks
I think the first method would work with this change:
UPDATE Country SET LawID_NEW = TRIM(CHAR(LawID));
ALTER TABLE tablename MODIFY columnname VARCHAR(20);
This works in mysql. Give it a try.
Or
ALTER TABLE table CHANGE columnname columnname VARCHAR(20);
I'm working with MS SQL SERVER 2003. I want to change a column in one of my tables to have fewer characters in the entries. This is identical to this question: Altering a Table Column to Accept More Characters except for the fact that I want fewer characters instead of more.
I have a column in one of my tables that holds nine-digit entries. A developer previously working on the table mistakenly set the column to hold ten-digit entries. I need to change the type from CHAR(10) to CHAR(9).
Following the instructions from the discussion linked above, I wrote the statement
ALTER TABLE [MY_TABLE] ALTER COLUMN [MY_COLUMN] CHAR(9);
This returns the error message "String or binary data would be truncated". I see that my nine-digit strings have a space appended to make them ten digits.
How do I tell SQL Server to discard the extra space and convert my column to a CHAR(9) type?
I think you get the error because there are some values in that table that are exactly 10 chars long (with no trailing spaces). Altering the table would thus cut these values to the length 9.
This is not allowed by default. If there only would be strings which would have some trailing spaces, there would be no problem with that.
So, if you are ok with cutting those values, do
UPDATE MY_TABLE SET MY_COLUMN = LEFT(MY_COLUMN, 9)
first, after that do the alter.
Disable Ansi Warnings before you alter your table.
SET ANSI_WARNINGS OFF
Beware that data will be truncated if you happen to have something 10 characters long.
Edit
Check existing lengths before actually changing the column length.
SET ANSI_WARNINGS OFF
GO
CREATE TABLE Test (Value CHAR(10))
INSERT INTO Test SELECT ('1234567890')
IF NOT EXISTS (SELECT * FROM Test WHERE LEN(Value) > 9)
ALTER TABLE Test ALTER COLUMN Value CHAR(9)
ELSE
SELECT LEN(Value), * FROM Test WHERE LEN(Value) > 9
DROP TABLE Test
The above 2 answers didn't work for me because I had a history table attached to the table I was trying to alter. This is what I did:
UPDATE MY_TABLE SET MY_COLUMN = LEFT(MY_COLUMN, 9)
ALTER TABLE MY_TABLE SET (SYSTEM_VERSIONING = OFF)
-- Might need to UPDATE MY_TABLEHistory SET MY_COLUMN = LEFT(MY_COLUMN, 9)
-- I didn't
ALTER TABLE MY_TABLEHistory ALTER COLUMN [MY_COLUMN] [varchar] (9) NULL
ALTER TABLE MY_TABLE SET (SYSTEM_VERSIONING = ON(HISTORY_TABLE = MY_TABLEHistory))
ALTER TABLE MY_TABLE ALTER COLUMN [MY_COLUMN] [varchar] (9) NULL