FLOAT 类型的精度

FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]

A small (single-precision) floating-point number. Allowable values are -3.402823466E+38 to -1.175494351E-38, 0, and 1.175494351E-38 to 3.402823466E+38. These are the theoretical limits, based on the IEEE standard. The actual range might be slightly smaller depending on your hardware or operating system.

M is the total number of digits and D is the number of digits following the decimal point. If M and D are omitted, values are stored to the limits allowed by the hardware. A single-precision floating-point number is accurate to approximately 7 decimal places.

UNSIGNED, if specified, disallows negative values.

Using FLOAT might give you some unexpected problems because all calculations in MySQL are done with double precision. See Section B.1.5.7, “Solving Problems with No Matching Rows”.

  FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]

小(单精度)浮点数。允许的值是-3.402823466E+38到-1.175494351E-38、0和1.175494351E-38到3.402823466E+38。这些是理论限制，基于IEEE标准。实际的范围根据硬件或操作系统的不同可能稍微小些。

M是小数纵位数，D是小数点后面的位数。如果M和D被省略，根据硬件允许的限制来保存值。单精度浮点数精确到大约7位小数位。如果指定UNSIGNED，不允许负值

从以上文档可知FLOAT类型在超过7位数的时候就会取近试值，一般是四舍五入的。