mysql中的to_char和to_number

 

BINARY str is shorthand for CAST(str AS BINARY).

Note that in some contexts, if you cast an indexed column to BINARY, MySQL is not able to use the index efficiently.

• CAST(expr AS type)

  The CAST() function takes a value of one type and produce a value of another type, similar to CONVERT(). See the description of CONVERT() for more information.

• CONVERT(expr,type), CONVERT(expr USING transcoding_name)

  The CONVERT() and CAST() functions take a value of one type and produce a value of another type.

  The type can be one of the following values:

  • BINARY[(N)]

  • CHAR[(N)]

  • DATE

  • DATETIME

  • DECIMAL[(M[,D])]

  • SIGNED [INTEGER]

  • TIME

  • UNSIGNED [INTEGER]