Virtually everything you do in MySQL involves data in some way or another because, by definition, the purpose of a database management system is to manage data. Even a statement as simple as
SELECT 1 involves evaluation of an expression to produce an integer data value.
Every data value in MySQL has a type. For example,
37.4 is a number and
'abc' is a string. Sometimes data types are explicit, such as when you issue a
CREATE TABLE statement that specifies the type for each column you define as part of the table:
CREATE TABLE mytbl ( int_col INT, # integer-valued column str_col CHAR(20), # string-valued column date_col DATE # date-valued column );
Other times data types are implicit, such as when you refer to literal values in ...