![]() In this article, we have discussed how to alter the column to increase or reduce the length of the column type of varchar in the Amazon AWS Redshift table. Let’s describe the table using a show statement to see the changes we have made to the Redshift table. # Changing the length of two fields at the same time. ![]() This example will change the data type of two fields at the same time. Note that the ALTER statement is used to update only one column at a time in AWS Redshift, if you wanted to change multiple column lengths, you need to write two statements. # ALTER the size of s_address from TABLE Students.ĪLTER COLUMN s_address type VARCHAR(200) Įxample 3: Alter two fields at the same time. In this example, we will ALTER the size of s_address from TABLE Students from varchar(20) to varchar(200). # ALTER the size of s_name from TABLE Students.Įxample 2: Alter the student address column. Here, we have changed the length of the student name from 10 to 100. In this example, we will increase the size of s_name column on the TABLE Students. Replace table_name, column_name, and new_column_type from above as per your need.Įxample 1: Alter the student name column size from VARCHAR(10) to VARCHAR(100). Since columns are part of the table, first you need to write the ALTER TABLE table_name, following ALTER COLUMN column_name, following TYPE new_column_type, and finally, end the statement with a semicolon. Also, While making changes to the table using ALTER statement you cannot insert or read the records from the table as it locks the table while altering. This allows only increasing VARCHAR column length and doesn’t support decreasing length. You can change the column length of Varchar in Amazon AWS Redshift by using ALTER COLUMN column_name TYPE clause from ALTER TABLE statement. # Inserting values into the Student TABLE ![]() The size of each column is different as we defined while creating the column. To insert values in the student TABLE, use INSERT INTO query, by using this we have added 5 student records. To add a new record to this table, we have to fill all the fields as they are set as not null which means it is compulsory to fill these fields. Prepare Table & Insert RecordsĬreate the Student TABLE with five columns named id, name, address, email, and grade. Next, alter the column data type by changing the size of the column to your desired size. The syntax is pretty easy to write the name of the TABLE you want to alter. The syntax for ALTER column to change the length in Amazon Redshift is as follows:ĪLTER TABLE TABLE_name ALTER COLUMN column_name TYPE new_data_type ![]() To reduce the column you may need to drop and add it as a new column with the desired reduced length. An important piece of information here is that ALTER only changes the varchar length hence, to change the type of a column you have to create a new column and drop the existing column.īy using ALTER statement you can only increase the length of the column but not reduce the length. Once your ALTER transaction is done you can do whatever you want to do with the TABLE. When you ALTER TABLE you are modifying the TABLE, so that you cannot read from and write in that TABLE. Note that ALTER TABLE locks the TABLE for read and write operations until a transaction completes. This TYPE clause in ALTER statement is used to update the length of the column of VARCHAR type in Redshift. To ALTER or change the length/size of a column in Amazon AWS Redshift use the ALTER COLUMN column_name TYPE clause in ALTER TABLE SQL statement. ![]()
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