When learning sql: There is this sentence:
Score Numeric (4,1)
, puzzled by how many, were troubled by irresponsible notes on old books
After Baidu search:
Numeric (X+y,y)
Where y is the number of decimal digits, x is the integer digits, and x+y is the total number of digits
Then: Numeric (4,1) Total number of digits is 4, where decimal 1 bits, Integer 4-1 = 3 bits
This is for numeric type data type, if the character type, binary data type, its
DataType (m)
The m in indicates length, occupies bytes, and the length of the number type is automatically specified by the SQL standard.
Microsoft TechNet's explanation is as follows: https://technet.microsoft.com/zh-cn/library/ms190476.aspx
Number of digits for precision, scale, and length (Transact-SQL) Other versions precision exponent words. decimal digits refers to the number of digits after the decimal point. For example, the precision of the number 123.45 is 5, and the scale number is 2. The default maximum precision for,numeric and decimal data types in SQL Server is 38. In earlier versions of SQL Server , the default maximum precision is 28. The length of the numeric data type is the number of bytes that are used to store this number. The length of the string or Unicode data type is the number of characters. The length of the binary, varbinary , and image data types is the number of bytes. For example, the,int data type can have 10 bits, which are stored with 4 bytes, and do not accept decimal points. The precision of the int data type is 10, the length is 4, and the number of decimal digits is 0. When two char, varchar, binary , or varbinary expressions are concatenated, the length of the generated expression is the sum of two source expression lengths, or the 8,000 character, In the least of them. When two nchar or nvarchar expressions are concatenated, the length of the generated expression is the sum of two source expression lengths, or the 4,000 character, in the case of the lesser of the two. When using union, except , or INTERSECT to compare two expressions of the same data type but with a different length, the resulting length is the larger of the two expressions. In addition to the decimal type, the precision and scale of numeric data types are fixed. If the arithmetic operator has two expressions of the same type, the result is that data type and has the precision and scale defined for this type. If an operator has two expressions of different numeric data types, the data type of the result is determined by the type precedence. results have the precision and scale defined for the data type. The following table defines when the result of the operation is decimal type, how to calculate the precision and scale of the result. When any of the following conditions are true, the result is decimal: Two expressions are decimal types. One expression is a decimal type, and the other is a data type that is lower than decimal priority. The operand expression is represented by the expression e1 (precision is  P1, the scale is  S1), and the expression e2 (precision is p2 and the scale is  S2). The precision and scale of any expression of non- decimal type, is the precision and scale defined for this expression data type.
numeric (x+y,y) length and number of digits