PDO预定义常量中有“整数”是什么？

Question

found from predefined constants. what is the (integer) means? why all (integer)?

PDO::PARAM_BOOL (integer)
Represents a boolean data type.
PDO::PARAM_NULL (integer)
Represents the SQL NULL data type.
PDO::PARAM_INT (integer)
Represents the SQL INTEGER data type.
PDO::PARAM_STR (integer)
Represents the SQL CHAR, VARCHAR, or other string data type.
PDO::PARAM_LOB (integer)
Represents the SQL large object data type.
PDO::PARAM_STMT (integer)
Represents a recordset type. Not currently supported by any drivers.
PDO::PARAM_INPUT_OUTPUT (integer)
Specifies that the parameter is an INOUT parameter for a stored procedure. You must bitwise-OR this value with an explicit PDO::PARAM_* data type.

Answer 1

That output (integer) just means that the underlying constant uses an integer value to differentiate itself from the other constants in that group.

For example, on my installation some of those constants have the following (integer) values:

PDO::PARAM_NULL = 0
PDO::PARAM_INT = 1
PDO::PARAM_BOOL = 5

Similarly you'll see that PDO::ATTR_DRIVER_NAME is listed as being of type string