在 -、+ 和 * 的情况下，如果两个操作数都是整数，则结果以 BIGINT（64 位）精度计算。In the case of -, +, and *, the result is calculated with BIGINT (64-bit) precision if both operands are integers.

如果两个操作数都是整数，并且其中任何一个是无符号的，则结果为无符号整数。对于减法，如果启用了 NO_UNSIGNED_SUBTRACTION SQL 模式，即使任何操作数是无符号的，结果也为有符号整数。If both operands are integers and any of them are unsigned, the result is an unsigned integer. For subtraction, if the NO_UNSIGNED_SUBTRACTION SQL mode is enabled, the result is signed even if any operand is unsigned.

如果 +、-、/、*、% 的任意一个操作数是实数或字符串值，则结果的精度为精度最大的操作数的精度。If any of the operands of a +, -, /, *, % is a real or string value, the precision of the result is the precision of the operand with the maximum precision.

在使用 / 进行除法运算时，当使用两个精确值操作数时，结果的小数位数等于第一个操作数的小数位数加上 div_precision_increment 系统变量的值（默认值为 4）。例如，表达式 5.05 / 0.014 的结果有六位小数（360.714286）。In division performed with /, the scale of the result when using two exact-value operands is the scale of the first operand plus the value of the div_precision_increment system variable (which is 4 by default). For example, the result of the expression 5.05 / 0.014 has a scale of six decimal places (360.714286).

+

加法：Addition:

mysql> SELECT 3+5;
        -> 8

-

减法：Subtraction:

mysql> SELECT 3-5;
        -> -2

-

一元负号。这个运算符会改变操作数的符号。Unary minus. This operator changes the sign of the operand.

mysql> SELECT - 2;
        -> -2

*

乘法：Multiplication:

mysql> SELECT 3*5;
        -> 15
mysql> SELECT 18014398509481984*18014398509481984.0;
        -> 324518553658426726783156020576256.0
mysql> SELECT 18014398509481984*18014398509481984;
        -> out-of-range error

最后一个表达式会产生错误，因为整数乘法的结果超出了 BIGINT 计算的 64 位范围。（参见 第 13.1 节，“数值数据类型”。）The last expression produces an error because the result of the integer multiplication exceeds the 64-bit range of BIGINT calculations. (See Section 13.1, “Numeric Data Types”.)

/

部门：Division:

mysql> SELECT 3/5;
        -> 0.60

除以零会产生一个 NULL 结果：Division by zero produces a NULL result:

mysql> SELECT 102/(1-1);
        -> NULL

仅当在将其结果转换为整数的上下文中执行时，除法才会使用 BIGINT 运算进行计算。A division is calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer.

DIVDIV

整数除法。舍弃除法结果中小数点右侧的任何分数部分。Integer division. Discards from the division result any fractional part to the right of the decimal point.

如果任一操作数是非整数类型，操作数将被转换为 DECIMAL，并使用 DECIMAL 算术进行除法运算，然后将结果转换为 BIGINT。如果结果超过 BIGINT 的范围，将发生错误。If either operand has a noninteger type, the operands are converted to DECIMAL and divided using DECIMAL arithmetic before converting the result to BIGINT. If the result exceeds BIGINT range, an error occurs.

mysql> SELECT 5 DIV 2, -5 DIV 2, 5 DIV -2, -5 DIV -2;
        -> 2, -2, -2, 2

N % M, N MOD M

取模运算。返回 N 除以 M 的余数。更多信息，请参见 MOD() 函数在 第 14.6.2 节，“数学函数” 中的描述。Modulo operation. Returns the remainder of N divided by M. For more information, see the description for the MOD() function in Section 14.6.2, “Mathematical Functions”.