What is Data Type?

What is meant by data type in database or programming languages? Datatype means what kind of data you want to store in that variable or column. For example, if you want to store the name of customer you most select string or varchar data type of that column, not number datatype.

How to Change the Datatype of the column?

SQL provides multiple ways to change your table columns datatype and want to add constraints in that column. We can easily change columns datatype through a simple query. Almost all the Database management systems provide queries as well as graphical user interfaces to change the datatypes of the columns.

Change the column datatype Using Query in SQL

To change the data type of a column, you can use the following query:

ALTER TABLE table_name

ALTER COLUMN column_name new_data_type ( size ) ;

The new datatype must be compatible with the old datatype of that column, otherwise, SQL gives you an error for modification of datatype.

Also, database management systems provide build-in functions to change the existed columns datatypes. Like this,

ALTER TABLE ‘ table_name ‘
MODIFY ‘ column_name ‘ ‘ New Data Type ‘  ;


ALTER TABLE Customer ALTER COLUMN Address char ( 100 ) ;


ALTER TABLE Customer MODIFY Address char ( 100 ) ;

How to Change the Datatype of the column in SQL workbench?

You can also change the data type of a column in SQL using the graphical user interface, you can change through these steps:

Click on the table and right-click on the schema of that table and then select the ALTER TABLE. A window will appear like this:

  • Select the column name available on the screen, edit this and click on apply.

You changed the datatype of the column.

How to change datatype in SQL after data is filled

It’s possible to change the datatype using Alter Column command, only if the new datatype is compatible for the old datatype otherwise SQL not give you permission to change the datatype.


You may change a column from varchar ( 50 ) to a varchar ( 200 ) not a number or date data type, the query is given below.


ALTER COLUMN ColumnName nvarchar ( 200 ) ;

How to Change the Column without Dropping a Table.

  • Create a new column and copy the data into this column.
  • Delete or drop the old column.
  • Change the name of the new column to old column


– – Add the new column


ADD DescriptionNew VARCHAR ( MAX )


– – Copy data to new column

Update TableName

SET DescriptionNew = Description


— Drop old column


DROP COLUMN Description


— Rename the new column to the original column’s name.

sp_RENAME ‘ TableName.DescriptionNew ‘ , ‘ Description ‘ , ‘ COLUMN ‘


This the simple and easy way to change the data type of any column and name of the column without dropping it.

How do you change the datatype of a SQL table?

To change the data type of a column in a table, use the following syntax:
  1. SQL Server / MS Access: ALTER TABLE table_name. ALTER COLUMN column_name datatype;
  2. My SQL / Oracle (prior version 10G): ALTER TABLE table_name. MODIFY COLUMN column_name datatype;
  3. Oracle 10G and later: ALTER TABLE table_name.

How do I convert one data type to another in SQL?

The CONVERT() function in SQL server is used to convert a value of one type to another type. It is the target data type to which the to expression will be converted, e.g: INT, BIT, SQL_VARIANT, etc. It provides the length of the target_type. Length is not mandatory.

How do I change data from numeric to character in SQL?

SQL has several built-in functions with which you can convert integer to character data.
  1. STR() The STR() function takes a number and turns it into characters, such as the following example shows:
  2. CONVERT()
  3. CAST()
  4. SQLite.

Can we convert varchar to int in SQL?

A varchar variable and an int variable are declared, then the value of the varchar variable is set. It converts varchar to int type with the help of cast and convert functions. The varchar variable must contain numeric characters. SELECT CAST(‘77788’ AS INT);

Can you sum varchar in SQL?

Once you convert it into any number datatype after that just perform any aggregate function on it. Lets SUM the column ([column varchar]) in the table (tbl_sample).

What does varchar do in SQL?

Also known as Variable Character, it is an indeterminate length string data type. It can hold numbers, letters and special characters. Microsoft SQL Server 2008 (and above) can store up to 8000 characters as the maximum length of the string using varchar data type.

How do I use Isnull in SQL?

SQL Server ISNULL() Function

The ISNULL() function returns a specified value if the expression is NULL. If the expression is NOT NULL, this function returns the expression.

Is type casting allowed in SQL?

A type conversion (casting) can render one or more indexes of the query useless. You can go ahead and check if an index is being used or not in the query plan using explain or explain extended . If the index is not being used, we can use explicitly type cast the column in the where clause or the join clause and so on.

Why is cast used in SQL?

The Cast() function is used to convert a data type variable or data from one data type to another data type. The Cast() function provides a data type to a dynamic parameter (?) or a NULL value. The data type to which you are casting an expression is the target type.

Which is better cast or convert in SQL?

CONVERT is SQL Server specific, CAST is ANSI. CONVERT is more flexible in that you can format dates etc. Other than that, they are pretty much the same. If you don’t care about the extended features, use CAST .

What is difference between cast and convert?

Both CAST and CONVERT are functions used to convert one data type to another data type. It is mainly used in the Microsoft SQL program, and both are often used interchangeably. The first difference between CAST and CONVERT is CAST is an ANSI standard while CONVERT is a specific function in the SQL server.

How do you multiply in SQL?

All you need to do is use the multiplication operator (*) between the two multiplicand columns ( price * quantity ) in a simple SELECT query. You can give this result an alias with the AS keyword; in our example, we gave the multiplication column an alias of total_price .

Can you do math in SQL?

Does SQL Server perform basic mathematical calculations? Yes – SQL Server can perform basic addition, subtraction, multiplication and division. In addition, SQL Server can calculate SUM, COUNT, AVG, etc. For these type of calculations, check out SQL Server T-SQL Aggregate Functions.

How do you do calculations in SQL?

You can use the string expression argument in an SQL aggregate function to perform a calculation on values in a field. For example, you could calculate a percentage (such as a surcharge or sales tax) by multiplying a field value by a fraction.

How do you cross join in SQL?

The CROSS JOIN joined every row from the first table (T1) with every row from the second table (T2). In other words, the cross join returns a Cartesian product of rows from both tables. Unlike the INNER JOIN or LEFT JOIN , the cross join does not establish a relationship between the joined tables.