SQL field type conversion

1、mysql  vchar turn int、double etc.

    MySQL Of CAST() Function can be used to get the value of a type , And produce another type of value

    cast() Function is a conversion function , The argument is an expression , It includes the use of AS Key separated source and target data types .

    cast   Convert to double type , about D\M Value considerations .   

# The formula 
CAST(value as type);
#vchar  turn  int  （ Decimals are rounded directly ）
CAST(value as SIGNED);
#vchar  turn  double  M  Represents the reserved integer digits + Keep the decimal places  ,D  Represents the number of decimal places reserved 
#1） Parameters m<65  It's the total number ,d<30 And  d<m  It's a decimal place .
#2）decimal The maximum possible value range is related to double  equally , Its valid value range is, however M  and D  Value determination of .
# If you change M  And fixed D, Then its value range will follow M  That's bigger and bigger .
CAST(value as decimal(M,D));

2、cast() Conversion type for function

 Binary system , Syntaxis binary The effect of prefixes  : BINARY    
 Character , With parameters  : CHAR()     
 date  : DATE     
 Time : TIME     
 Date time type  : DATETIME     
 Floating point numbers  : DECIMAL      
 Integers （ A signed ） : SIGNED     
 Unsigned integer  （ Unsigned ）: UNSIGNED 

3、cast() and convert() Comparison

     The same thing ： It's all data type conversion , The functions realized are basically the same as

     Difference ： The grammar of the two is different ,cast(value as type) 、 convert(value,type)

 

If there are errors or inaccurate descriptions , Please correct me .