I have a program with [msaccess] and i need rename the column of a table. The problem is that i can not rename with a sql statement if the column is indexed, so I have to delete the index.
To delete the index i use:
ALTER TABLE SuministroProductos DROP CONSTRAINT Index_84793306_29F5_4DFF
But not in all versions, does the index have the same name.
So, how can i know the name of the index in each table?
Is there another way of renaming the column? I need with SQL instructions in access.
Thank you
EDIT:
This work:
DROP INDEX Index_BB8ACAF4_28D7_4339 ON SuministroProductos
But this not work:
DROP INDEX Index_* ON SuministroProductos
The following code will iterate through the indexes of your table.
For i = 0 to CurrentDb.TableDefs("SuministroProductos").Indexes.Count - 1
IndexArray(i) = CurrentDb.TableDefs("SuministroProductos").Indexes(i).Name
Next
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.
In other databases such as MySQL I could just do this:
ALTER TABLE demo RENAME INDEX old_index TO new_index
What's the best workaround for SQLite?
Update
SQLite does not seem to support this syntax. In which case is there a work around I can use. For example:
DROP INDEX old_index;
CREATE INDEX new_index ON demo(col1, col2);
The issue with the above is that I need to manually find out which columns were indexed. I want something that can be done automatically like:
set columns = select columns indexed by old_index;
DROP INDEX old_index;
CREATE INDEX new_index ON demo(columns);
SQLite's ALTER TABLE does not support this. Just recreate it:
DROP INDEX old_index;
CREATE INDEX new_index ON demo([...]);
You can get the index definition from the schema:
SELECT sql FROM sqlite_master WHERE type = 'index' AND name = 'old_index';
But there is no mechanism to modify and execute the result from inside SQLite.
How can I change DATA TYPE of a column from number to varchar2 without deleting the table data?
You can't.
You can, however, create a new column with the new data type, migrate the data, drop the old column, and rename the new column. Something like
ALTER TABLE table_name
ADD( new_column_name varchar2(10) );
UPDATE table_name
SET new_column_name = to_char(old_column_name, <<some format>>);
ALTER TABLE table_name
DROP COLUMN old_column_name;
ALTER TABLE table_name
RENAME COLUMN new_column_name TO old_coulumn_name;
If you have code that depends on the position of the column in the table (which you really shouldn't have), you could rename the table and create a view on the table with the original name of the table that exposes the columns in the order your code expects until you can fix that buggy code.
You have to first deal with the existing rows before you modify the column DATA TYPE.
You could do the following steps:
Add the new column with a new name.
Update the new column from old column.
Drop the old column.
Rename the new column with the old column name.
For example,
alter table t add (col_new varchar2(50));
update t set col_new = to_char(col_old);
alter table t drop column col_old cascade constraints;
alter table t rename column col_new to col_old;
Make sure you re-create any required indexes which you had.
You could also try the CTAS approach, i.e. create table as select. But, the above is safe and preferrable.
The most efficient way is probably to do a CREATE TABLE ... AS SELECT
(CTAS)
alter table table_name modify (column_name VARCHAR2(255));
Since we can't change data type of a column with values, the approach that I was followed as below,
Say the column name you want to change type is 'A' and this can be achieved with SQL developer.
First sort table data by other column (ex: datetime).
Next copy the values of column 'A' and paste to excel file.
Delete values of the column 'A' an commit.
Change the data type and commit.
Again sort table data by previously used column (ex: datetime).
Then paste copied data from excel and commit.
I am going to perform a table-wide update on a huge table (+200Millon records) so I am going to populate the data via SELECT into a separate table, than drop the original and rename the new one.
In one of the articles someone mentioned that it is better to create the new table with the same name in a temporary schema (e.g. 'clone') and switch it to the used one (e.g. 'dbo'), than to use the original schema with a temporary name and call sp_rename after the data is in place and the old table is dropped.
I was looking into this, but I cannot think of anything why the schema switch is better than the sp_rename. Can anyone find any good reason why is better to use the first or the second approach?
Thanks!
EDIT: I want to update the values in a specific column
EDIT2: Ultimately my question is, if I decide to go down the way of creating a new table to transfer data to which alternative to use:
CREATE TABLE dbo.newTable
...
DROP TABLE dbo.originalTable
EXEC sp_rename N'dbo.newTable', N'dbo.originalTable'
OR
CREATE TABLE clone.originalTable
...
DROP TABLE dbo.originalTable
ALTER SCHEMA dbo TRANSFER clone.originalTable
By the way, I would suggest that you WON'T populate the table by using SELECT * INTO. This will lock your source table for everyone else during the insertion, which could take quite a time.
Just a suggestion, try this instead:
SELECT TOP 0 INTO [newTable]
FROM [oldTable]
INSERT INTO [newTable]
SELECT * FROM [oldTable]
By the way, you can use sp_rename to rename your table to another name. But it won't change the schema. If you try to change the schema too it will produce a buggy table name.
You can instead try to move the table to another name. Example below:
EXEC sp_rename N'oldTable', N'oldTable_Backup'
EXEC sp_rename N'newTable', N'oldTable'
Hopefully this will help you.
Based on your edited answer the quickest way to do that is:
If you have to include default value to the column
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
[WITH VALUES]
and then drop the old column from the table.
ALTER TABLE {TABLENAME} DROP COLUMN {OLD COLUMN}
If you have to update table column based calculated values
Disable index on the column which you are updating
Create index on the column which are in WHERE clause
Update statistics
Use WITH(NOLOCK) table hint [if you are fine with dirty read]
Update
As per edit 2, your first statement is about changing table name and second statement is about changing schema. They both are different and does not related to moving data or updating value. In this case, changing schema would be the best bet
If locking was an issue before it still is regardless of what version SQL Server that you are using. When you drop and rename you are also losing all the rights on the table.
I have a requirement where I want to rename a column. In in this case, it should happen like:
1.) I need to create a new column with the existing column structure.
2.) Migrate the data to the new column.
3.) Retain the old column.
I don't have the new column structure and I have to take it from the old column.
TIA.
You don't need to select into the same table. Perform the following steps:
Create the new column as nullable.
Use an update statement to fill the data into the new column based on the values from the old column.
Add a non-nullable constraint, if appropriate.
Update all queries and code to use the values in the new column instead of the old column.
Remove the old column.
What version of Oracle? You can rename the column since 9i R2:
ALTER TABLE your_table
RENAME COLUMN old_name to new_name;
If you're set on recreating the table so you can use SELECT INTO, then you'd want to use the following steps:
Drop constraints related to the table(s)
Drop indexes related to the table(s)
Lock the original table:
LOCK TABLE old_table IN EXCLUSIVE MODE;
Rename the table:
RENAME old_table TO old_table_orig
Create the new table with the correct/updated columns
Run your SELECT INTO script(s) to populate the new table, handling data type changes if there are any
Add indexes
Add constraints
Drop the old_table_orig