Add note about SELECT CAST(MeN AS CHAR) incompatibility (pingcap#13518)

data-type-date-and-time.md

@@ -171,7 +171,7 @@ CREATE TABLE t1 (
 
 ## Decimal part of time value
 
-`DATETIME` and `TIMESTAMP` values can contain a fractional part of up to 6 digits which is accurate to milliseconds. In any column of `DATETIME` or `TIMESTAMP` types, a fractional part is stored instead of being discarded. With a fractional part, the value is in the format of 'YYYY-MM-DD HH:MM:SS[.fraction]', and the fraction ranges from 000000 to 999999. A decimal point must be used to separate the fraction from the rest.
+`DATETIME` and `TIMESTAMP` values can contain a fractional part of up to 6 digits which is accurate to microseconds. In any column of `DATETIME` or `TIMESTAMP` types, a fractional part is stored instead of being discarded. With a fractional part, the value is in the format of 'YYYY-MM-DD HH:MM:SS[.fraction]', and the fraction ranges from 000000 to 999999. A decimal point must be used to separate the fraction from the rest.
 
 + Use `type_name(fsp)` to define a column that supports fractional precision, where `type_name` can be `TIME`, `DATETIME` or `TIMESTAMP`. For example,