I was just surfing the net and found a query something like:
sql = "select milk_rate from special_milk_rate
where code_producer_id=? and effective_from <= ?
and effective_till >= ?"
what exactly this query means i means what is the use of ? in this statement.
and one thing more what is use of & in sql.
This usually implies a prepared statement, where the parameters are filled in later. (see e.g. http://en.wikipedia.org/wiki/Prepared_statements#Parameterized_statements).
what exactly this query means i means what is the use of ? in this statement.
The question marks are for parameters.
and one thing more what is use of & in sql.
& is a bitwise AND operator in sql
Question marks are found in prepared statements, meaning it is parametrized and can be called again and again without having to reconstruct the whole sql statement, just by changing the parameters. Some frameworks use those that together with SqlCommands. Those encapsulate escaping and prevent sql injection attacks.
Some frameworks also allow named parameters.
The question marks are supposed to contain the actual parameters.
E.g.
"select milk_rate from special_milk_rate
where code_producer_id=2 and effective_from <= '20101231'
and effective_till >= '20110124'"
Here is nice article:
In some statements, parameters are unknown when the statement is prepared because a different value can be inserted each time the statement is executed. In these statements, you can use a question-mark ( ? ) placeholder where a parameter must be supplied when the statement is executed.
& usually denotes a variable or substitution value which you may be prompted for at run time
