Summary: in this tutorial, you will learn how to use the SQL Server 6 statement to modify a column of a table. SQL Server allows you to perform the following changes to an existing column of a table:
Modify column’s data typeTo modify the data type of a column, you use the following statement:
The new data type must be compatible with the old one, otherwise, you will get a conversion error in case the column has data and it fails to convert. See the following example. First, create a new table with one column whose data type is 8:
Second, insert some rows into the table:
Second, modify the data type of the column from 8 to 0:
Third, insert a new row with a character string data:
Fourth, modify the data type of the column from 0 back to 8:
SQL Server issued the following error:
Change the size of a columnThe following statement creates a new table with one column whose data type is 3:
Let’s insert some sample data into the t2 table:
You can increase the size of the column as follows:
However, when you decrease the size of the column, SQL Server checks the existing data to see if it can convert data based on the new size. If the conversion fails, SQL Server terminates the statement and issues an error message. For example, if you decrease the size of column 4 to 5 characters: 0 SQL Server issued the following error: 1 Add a CREATE TABLE t1 (c INT); Code language: SQL (Structured Query Language) (sql)7 constraint to a nullable columnThe following statement creates a new table with a nullable column: 2 The following statement inserts some rows into the table: 3 If you want to add the 7 constraint to the column 4, you must update NULL to non-null first for example: 4 And then add the 7 constraint: 5 In this tutorial, you have learned how to use the SQL Server 6 to modify some properties of an existing column. How do you change the datatype of a column with data?Select the field (the column) that you want to change. On the Fields tab, in the Properties group, click the arrow in the drop-down list next to Data Type, and then select a data type. Save your changes.
How to change column datatype in SQL database without losing data?So to do that go to SQL Server and within Tools select Options. Now in the options window expand Designers and under "Table and Database Designers" uncheck the check box "Prevent saving changes that require table re-creation" then click OK.
How to change column datatype in Oracle without losing data?Alter the table by adding another column with varchar datatype.. Update the new column with the old column.. Drop the old column.. Rename the new column name to old column name.. Which syntax will modify the data type of an already existing column?The basic syntax of an ALTER TABLE command to change the DATA TYPE of a column in a table is as follows. ALTER TABLE table_name MODIFY COLUMN column_name datatype; The basic syntax of an ALTER TABLE command to add a NOT NULL constraint to a column in a table is as follows.
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