MySQL 5.1, which is the code base
described by this documentation, the statements
GET DIAGNOSTICS are not supported.
Implementing these features will have some impact on the
material described here, so changes in later versions are
When the code enters a block of logic guarded by an SQL exception handler, the state or the runtime context in the interpreter changes, to represent this fact. The state change is not apparent immediately, it will only become apparent if an exception is raised. The internal runtime state of the engine also changes when the code leaves a block that contains an exception handler.
How exception handlers work during runtime is the subject of
another section (see Section 16.7.4, “Exception Handling”). What
is described here is the state maintained internally, to
HANDLER is currently “active”,
The SQL precedence rules for
dictates that the last installed (inner most) handler is
always considered first, so the natural structure to represent
what handler is active is a stack,
In addition, some extra information is required for
CONTINUE handlers: the
“address” in the code, or instruction pointer in
sp_instr array, of where to resume
execution when the handler returns. This data is maintained in
sp_rcontext::m_hsp, which again is a
stack because exception handlers can be
nested (exceptions can be raised and
trapped during the execution of the body
of an exception handler, too).