Changing the maximum length of a varchar column?

Question

I'm trying to update the length of a varchar column from 255 characters to 500 without losing the contents. I've dropped and re-created tables before but I've never been exposed to the alter statement which is what I believe I need to use to do this. I found the documentation here: ALTER TABLE (Transfact-SQL) however I can't make heads or tails of it.

I have the following so far (essentially nothing unfortunately):

alter table [progennet_dev].PROGEN.LE
alter column UR_VALUE_3

How do I approach this? Is there better documentation for this statement out there (I did some searches for an example statement but came up empty)?

Answer 1

You need

ALTER TABLE YourTable ALTER COLUMN YourColumn <<new_datatype>> [NULL | NOT NULL]

But remember to specify NOT NULL explicitly if desired.

ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500) NOT NULL;

If you leave it unspecified as below...

ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500);

Then the column will default to allowing nulls even if it was originally defined as NOT NULL . ie omitting the specification in an ALTER TABLE ... ALTER COLUMN is always treated as.

ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500) NULL;

This behaviour is different from that used for new columns created with ALTER TABLE (or at CREATE TABLE time). There the default nullability depends on the ANSI_NULL_DFLT settings.

Answer 2

Increasing column size with ALTER will not lose any data:

alter table [progennet_dev].PROGEN.LE 
    alter column UR_VALUE_3 varchar(500) 

As @Martin points out, remember to explicitly specify NULL | NOT NULL NULL | NOT NULL

Answer 3

You can use modify :

ALTER TABLE `table name` 
modify COLUMN `column name` varchar("length");

Answer 4

ALTER TABLE TABLE_NAME MODIFY COLUMN_NAME VARCHAR(40);

Late to the question - but I am using Oracle SQL Developer and @anonymous's answer was the closest but kept receiving syntax errors until I edited the query to this.

Hope this helps someone

Answer 5

In Oracle SQL Developer

ALTER TABLE car_details MODIFY torque VARCHAR(100);

Answer 6

在 IntelliJ 中使用 Maria-DB 和 DB-Navigator 工具， MODIFY Column对我有用，而不是Alter Column

Answer 7

I was also having above doubt, what worked for me is

ALTER TABLE `your_table` CHANGE `property` `property` 
VARCHAR(whatever_you_want) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL;  

Answer 8

这在 db2 中对我有用：

alter table "JOBS"  alter column "JOB_TITLE" set  data type varchar(30);

Answer 9

As an alternative, you can save old data and create a new table with new parameters.

In SQL Server Management Studio: "your database" => task => generatescripts => select specific database object => "your table" => advanced => types of data to script - schema and data => generate

Personally, I did so.

Answer 10

For MariaDB, use modify column :

ALTER TABLE table_name MODIFY COLUMN column_name VARCHAR (500);

It will work.