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Data formatting

SQL Conversion Functions

What are SQL Conversion Functions?

SQL Conversion Functions, also known as data type conversion or casting functions, are used to change the data type of a value from one type to another. These functions allow you to convert data from one data type to another data type, which is particularly useful when you need to ensure data compatibility or when performing operations that require data in a specific format.

When you would use it

You would use SQL Conversion Functions when you need to:

  1. Ensure data compatibility: Convert data from one data type to another to ensure that data types match when performing operations or storing data.

  2. Manipulate data: Change the data type temporarily for a specific operation or calculation.

  3. Control output format: Format data for presentation or reporting purposes, such as converting a date to a specific string format.

  4. Compare data: Make comparisons between values of different data types, which often requires conversion to a common data type.

  5. Aggregate data: Convert data to a common type for aggregation functions like sum or average.

  6. Handle user input: Convert user input from string format to the appropriate data type for storage or calculation.


SQL Conversion Functions are typically used in SQL queries and follow a general syntax:

CONVERSION_FUNCTION(data, target_data_type)
  • CONVERSION_FUNCTION: The specific conversion function you want to use (e.g., CAST, CONVERT, or a vendor-specific function).
  • data: The value or expression you want to convert.
  • target_data_type: The data type to which you want to convert the data.

Parameter values

  • CONVERSION_FUNCTION: Select the appropriate conversion function for your database system.
  • data: The value or expression you want to convert. This can be a column, constant, or expression.
  • target_data_type: Specify the data type to which you want to convert the data.

Example query

Suppose you have a column "price" with data in string format, and you want to convert it to a numeric data type for calculations. You can use the CAST function in PostgreSQL as an example:

SELECT CAST(price AS NUMERIC) AS numeric_price
FROM products;

Example table response

The result of the query will display the "price" values in numeric format:

| numeric_price |
| ------------  |
| 12.99         |
| 24.50         |
| 199.00        |

Use cases

  • Ensuring data compatibility by converting data from one data type to another.
  • Changing data types for specific calculations or operations.
  • Formatting data for presentation or reporting purposes.
  • Making comparisons between values of different data types.
  • Converting data to a common type for aggregation functions.
  • Handling user input by converting it to the appropriate data type.

SQL languages this is available for

SQL Conversion Functions are a common feature supported by many relational database management systems (RDBMS) and SQL database systems. They are available in:

  • PostgreSQL
  • MySQL
  • SQL Server
  • Oracle Database
  • SQLite
  • IBM Db2
  • MariaDB

The specific conversion functions and syntax may vary slightly between different database systems, so it's essential to consult the documentation for your specific database system for precise details.


SQL Date Formatting

SQL Numeric Value Types

SQL String Types

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