What is the difference among length, precision, and scale in an SQL server?

 In SQL Server, length, precision, and scale are attributes that define the characteristics of data types, particularly numeric and string data types. Here's the distinction among them:

1. Length

• Definition: Refers to the maximum size or number of characters a data type can hold.
• Applies To: Primarily string data types (e.g., CHAR, VARCHAR, NCHAR, NVARCHAR), binary data types (e.g., BINARY, VARBINARY), and some others like VARIANT.
• Example:

  VARCHAR(50) -- Can hold up to 50 characters.
  NCHAR(20) -- Can hold up to 20 Unicode characters.
  

• For binary types, length refers to the number of bytes.

---

2. Precision

• Definition: Specifies the total number of significant digits in a number.
• Applies To: Numeric data types such as DECIMAL and NUMERIC.
• Example:

  DECIMAL(10, 2) -- Precision = 10 (can store up to 10 total digits).
  

  In this example, you could store numbers like 12345678.90 (8 digits before the decimal point + 2 digits after).

---

3. Scale

• Definition: Specifies the number of digits to the right of the decimal point.
• Applies To: Numeric data types such as DECIMAL and NUMERIC.
• Example:

  DECIMAL(10, 2) -- Scale = 2 (2 digits allowed after the decimal point).
  

  In this example, numbers like 12345678.90 are valid, but numbers like 123.456 would be truncated or rounded depending on the operation.

---

Interrelationship of Precision and Scale

• Precision defines the total number of digits, while scale specifies how many of those digits are to the right of the decimal.
• If you define DECIMAL(10, 2), it means:
  • Total digits allowed = 10.
  • Out of those, 2 digits are reserved for the fractional part.
  • This leaves 8 digits for the integer part.

---

Key Points

1. Length is for size (characters or bytes).
2. Precision and scale are for numeric accuracy.
3. Scale cannot exceed precision (e.g., DECIMAL(5, 6) is invalid because the scale exceeds the precision).

Let me know if you want examples or further clarification!