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review for MDEV-14564: Support FOR loop in stored aggregate functions
I was recently assigned as a reviewer for this patch:
I have some suggestions.
1. The MDEV says the proposed syntax is:
FOR GROUP ROWS DO
and you implemented:
FOR GROUP NEXT ROW DO
I think the syntax on MDEV looks better.
2. I don't like that you're adding a new uint member
An instruction processing a 'FETCH GROUP NEXT ROW' statement
does not need it.
3. The generated code:
+show function code f1;
+0 set total at 1 0
+1 jump_if_not 5(5) 1
+3 set total@1 total@1 + a@0
+4 jump 1
+5 freturn int total at 1
does not look nice.
- The command at position 2 must have a name.
- The command at position 1 looks like a hack.
The underlying code is:
+ if (! it->val_bool() || thd->spcont->forced_error)
So it is a conditional jump which never jumps on the condition,
It jumps only on thd->spcont->forced_error.
Please create a new class sp_instr_agg_cfetch_or_jump,
derive it from sp_instr,
and add m_dest to this class.
Please implement print() and execute() for it.
print() should display:
- the name of the command, "agg_cfetch_or_jump".
- the label where it jumps to when 'no rows' happens.
Note, sp_instr_agg_cfetch_or_jump will have almost nothing to share
with the old sp_instr_agg_cfetch.
So sp_instr_agg_cfetch_or_jump should derive from sp_instr,
not from sp_instr_agg_cfetch.
Please perform jump to a proper position on 'no more rows'
just inside sp_instr_agg_cfetch_or_jump::execute()
So the code should look about like this:
0 set total at 1 0
1 agg_cfetch_or_jump 4
2 set total@1 total@1 + a@0
3 jump 1
4 freturn int total at 1
4. As discussed on slack, the name for the command sp_instr_agg_cfetch
was probably a not good choise. The "c" in other commands like:
is an abbreviation for the word "cursor".
sp_instr_agg_cfetch does not use any cursors (i.e. sp_cursor instances).
Please rename sp_instr_agg_cfetch to sp_instr_fetch_group_row.
And the new command can be named something like:
sp_instr_fetch_group_row_or_jump, instead of sp_instr_agg_cfetch_or_jump.