MySQL FORMAT Expressions

The `FORMAT` expression in MySQL is used to format numbers to a specified number of decimal places, adding commas as thousands separators. It is particularly useful for enhancing the readability of numerical data in SQL queries.

Usage

The `FORMAT` expression is typically used when you need to display numbers in a more human-readable format, especially for financial and statistical reports. It converts a number to a string with a specified number of decimal places, including locale-based thousands separators.

FORMAT(number, decimal_places)

In this syntax, `number` is the numeric value to be formatted, and `decimal_places` specifies the number of decimal places to retain.

Examples

1. Basic Formatting

SELECT FORMAT(1234567.89, 2);

This example formats the number `1234567.89` to `1,234,567.89`, adding commas as thousands separators and retaining two decimal places.

2. Formatting with Zero Decimals

SELECT FORMAT(98765.4321, 0);

Here, the number `98765.4321` is formatted as `98,765`, rounding the number to the nearest whole number and removing decimal places.

3. Formatting with Locale

SELECT FORMAT(1234567.89, 2, 'de_DE');

This example formats `1234567.89` to `1.234.567,89` using the German locale, which uses a period as a thousands separator and a comma as a decimal point.

Tips and Best Practices

• Consider Performance. Using `FORMAT` can impact performance when applied to large datasets, so use it judiciously. In cases where performance is critical, consider formatting numbers in your application layer instead.
• Locale Usage. Always specify a locale if you need specific formatting conventions for different countries.
• Use for Display Only. Remember that `FORMAT` returns a string, so it should be used for display purposes rather than further numerical calculations.
• Consistent Decimal Places. Ensure consistency in the number of decimal places across your dataset for uniformity and clarity.
• Error Handling. If non-numeric values are passed to the `FORMAT` function, it will result in an error. Similarly, using an invalid locale string will default to the standard locale. Always validate inputs to prevent errors.