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How Do You Change Data Type to Integer?

Published in Database Data Types 5 mins read

You can change a data type to integer either by altering the column definition in a table or by casting a specific value temporarily within a query.

Changing a data type to integer can mean two different things:

  1. Changing the data type of an entire column in a database table. This is a permanent change that affects all existing and future data in that column.
  2. Casting a specific value to an integer type within a query. This is a temporary conversion used for calculations, comparisons, or display purposes, and it does not affect the original data storage type.

Let's look at how to achieve both based on common database practices, incorporating the reference information.

Changing a Column's Data Type Using ALTER TABLE

To permanently change the data type of a column in your database table to INTEGER, you use the ALTER TABLE statement.

Reference Information:

  • You must include information from the reference(s) in your answer: You can use ALTER TABLE to change the data type to INTEGER. The conversion changes the data type of all values that currently exist in the column and any new values that might be added.

When you use ALTER TABLE to change a column's type to INTEGER, the database system attempts to convert all existing values in that column. If a value cannot be converted (e.g., text that isn't a number), the operation might fail or result in errors or null values, depending on the specific database system.

Syntax for ALTER TABLE

The exact syntax can vary slightly between database systems (like PostgreSQL, MySQL, SQL Server, etc.), but the general structure is:

ALTER TABLE table_name
ALTER COLUMN column_name TYPE new_data_type;

Or, in some systems (like MySQL):

ALTER TABLE table_name
MODIFY COLUMN column_name new_data_type;

For changing to INTEGER:

ALTER TABLE your_table_name
ALTER COLUMN your_column_name TYPE INTEGER;

(Note: Replace your_table_name and your_column_name with your actual table and column names.)

Practical Example

Suppose you have a table named products with a column price stored as VARCHAR (text), and you want to change it to INTEGER.

-- Before: price might contain '10', '25.50', 'N/A'
-- Target: Change price to INTEGER
ALTER TABLE products
ALTER COLUMN price TYPE INTEGER;

Important Considerations:

  • Ensure existing data is compatible with the INTEGER type. Non-integer data might cause the ALTER TABLE statement to fail.
  • This operation can take time on large tables and might lock the table during execution.
  • Always test schema changes on a development or staging environment before applying them to production.

Casting a Value to INTEGER in a Query

Casting allows you to convert a value from one data type to another temporarily within the context of a query. This is useful for calculations, comparisons, or when you need data in a specific format for an application, without changing the underlying stored data type.

Reference Information:

  • Use the CAST AS keywords or the double colon (::) cast operator to cast a value to a different data type.

Using CAST AS

The standard SQL way to cast a value is using the CAST() function with the AS keyword.

Syntax for CAST AS

CAST(value AS new_data_type)

For casting to INTEGER:

CAST(your_value AS INTEGER)

Example using CAST AS

If you have a column quantity_text stored as text and you want to perform a calculation using it as a number:

SELECT
    product_name,
    CAST(quantity_text AS INTEGER) * price AS total_value
FROM
    order_items;

This query treats quantity_text as an integer for the calculation but doesn't change how it's stored in the order_items table.

Using the Double Colon (::) Operator

Many database systems, particularly PostgreSQL, support a shorthand syntax for casting using the double colon ::.

Syntax for ::

value::new_data_type

For casting to INTEGER:

your_value::INTEGER

Example using ::

Using the same scenario as above with the :: operator:

SELECT
    product_name,
    quantity_text::INTEGER * price AS total_value
FROM
    order_items;

Both CAST(value AS INTEGER) and value::INTEGER achieve the same result of temporarily converting a value to an integer within the query.

Summary Table: ALTER vs. CAST

Feature ALTER TABLE CAST AS / ::
Purpose Change column's stored data type Convert value temporarily within a query
Permanence Permanent change to schema Temporary; affects only the query execution
Applies To All values in a column (current & future) A specific value or expression
Syntax ALTER TABLE ... TYPE INTEGER CAST(value AS INTEGER) or value::INTEGER
Effect Modifies table structure Modifies data representation during query

In conclusion, choose ALTER TABLE when you need to permanently store data in a column as an integer, and use CAST AS or :: when you need to treat a value as an integer for a specific operation in a query without changing its original storage type.

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