Conclusion

In this chapter we reviewed the facilities MySQL provides for including SQL within stored programs. The following types of SQL statements can appear in stored programs:

• Simple embedded non-SELECT statements, including DML statements (INSERT, DELETE, UPDATE) and DDL statements (CREATE, DROP, ALTER, etc.) can be included within stored programs without any particular restrictions.
• SELECT statements that return only one row may include an INTO clause that stores the results of the SELECT statement into stored program variables.
• SELECT statements allow you to iterate through the rows returned by a multirow SELECT statement by using a cursor. Cursors involve a bit more programming effort, including a looping structure and a condition handler to prevent "no data to fetch" errors when all rows from the cursor have been retrieved. Nevertheless, cursors will probably be your main mechanism for performing complex data processing in stored programs.
• "Unbounded" SELECT statementsthose without an INTO clause or a CURSOR statementcan be included within stored procedures (but not within stored functions). The output from these SELECT statements will be returned to the calling program (but not to a calling stored procedure). You will need to employ special code in your calling program to handle result sets from stored procedures, especially if more than a single result set is returned.

SQL statements can also be prepared dynamically using MySQL server-side prepared statements.

If your SQL statements generate an error, your stored program will terminate and return control to the calling program unless you create an error handler that "catches" the error and takes appropriate action. We saw a simple example of an error handler in this chapter and looked at NOT FOUND handlers that handle the end of a cursor result set. In the next chapter we'll cover the topic of error handlers in greater detail.