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/*! \page stat Preparing and Executing Statements
\section stat_prep Creating a Statement
The cppdb::statement objects are usually created by calling cppdb::session::prepare() function or by using
cppdb::session::operator<<(). Prepare statements are usually cached for future reuse. Non-prepared statements
can be also created by calling cppdb::session::create_statement() and prepared statements can be created without
caching by calling cppdb::session::create_prepared_uncached_statement(). It is useful when
such statements are rarely executed or executed only once.
For example:
\code
cppdb::statement st=sql.prepare("DELETE FROM users");
\endcode
\section stat_bind Binding Parameters
The statement may contain placeholders marked with "?" for parameters that should be binded. The
values for placeholders can be binded by their order using cppdb::statement::operator<<() or \ref cppdb::statement "bind()"
functions. The placeholder order can be also specified explicitly starting from 1.
For example:
\code
cppdb::statement st=sql.prepare("DELETE FROM users WHERE age<? AND role<>?");
st.bind(1,13);
st.bind(2,"moderator");
\endcode
Of course syntactic sugar may be used as well:
\code
cppdb::statement st=sql << "DELETE FROM users WHERE age<? AND role<>?" << 13 << "moderator";
\endcode
\section stat_null Binding NULL values.
- You can use cppdb::statement::bind_null() functions.
\n
\code
cppdb::statement st=sql << "INSERT into f(x) values(?)";
st.bind_null(1);
\endcode
- You can use manipulator cppdb::null
\n
\code
sql << "INSERT into f(x) values(?)" << cppdb::null << cppdb::exec;
\endcode
- If you have an information about wether the value is null or not only at run time you can use a cppdb::use() manipulator
which receives a value and a parameter of cppdb::null_tag_type.
\n
\code
cppdb::null_tag_type tag = value_is_null ? cppdb::null_value : cppdb::not_null_value;
sql << "INSERT into f(x) values(?)" << cppdb::use(value,tag) << cppdb::exec;
\endcode
\section stat_exec Executing Statements
Statements are executed by calling cppdb::statement::exec(). Also manipulator cppdb::exec provided
for execution of a statement that allows writing complex queries in one line.
\code
sql << "DELETE FROM users WHERE age<? AND role<>?" << 13 << "moderator" <<cppdb::exec;
\endcode
\section stat_meta Fetching Meta-data
Meta-data about recently executed statement can fetched using following functions:
- cppdb::statement::affected() - the number of rows affected by the statement
- cppdb::statement::last_insert_id() - the last generated row id.
- cppdb::statement::sequence_last() - the last generated sequence number (using named sequences).
\section stat_reset Reusing Statement
The same prepared statement can be reused multiple times. For this purpose after each call of ppdb::statement::exec() or ppdb::statement::query(), ppdb::statement::reset() should be called that would clear all bindings and allow executing it once again:
\code
cppdb::statement st = sql << "INSERT INTO students(id,name) values(?,?)";
for(i=0;i<students.size();i++) {
st.bind(students[i].id);
st.bind(students[i].name);
st.exec();
st.reset();
}
\endcode
*/
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