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translate: special case for LIMIT 0

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Fixes #55
This commit is contained in:
Piotr Sarna
2024-07-06 10:43:41 +02:00
parent 095bf494f3
commit 5bd3d283d1
1 changed files with 28 additions and 16 deletions
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44
core/translate.rs
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@@ -122,8 +122,16 @@ fn translate_select(select: Select) -> Result<Program> {
None
};
let cursor_id = program.alloc_cursor_id();
let limit_decr_insn = match select.from {
Some(table) => {
let parsed_limit = select.limit.as_ref().and_then(|limit| {
if let ast::Expr::Literal(ast::Literal::Numeric(num)) = &limit.expr {
num.parse::<i64>().ok()
} else {
None
}
});
let limit_insn = match (parsed_limit, select.from) {
(Some(0), _) => Some(program.emit_placeholder()),
(_, Some(table)) => {
let root_page = table.root_page;
program.emit_insn(Insn::OpenReadAsync {
cursor_id,
@@ -134,7 +142,7 @@ fn translate_select(select: Select) -> Result<Program> {
let rewind_await_offset = program.emit_placeholder();
let (register_start, register_end) =
translate_columns(&mut program, Some(cursor_id), &select);
let limit_decr_insn = if select.exist_aggregation {
let limit_insn = if select.exist_aggregation {
program.emit_insn(Insn::NextAsync { cursor_id });
program.emit_insn(Insn::NextAwait {
cursor_id,
@@ -161,13 +169,13 @@ fn translate_select(select: Select) -> Result<Program> {
start_reg: register_start,
count: register_end - register_start,
});
let limit_decr_insn = limit_reg.map(|_| program.emit_placeholder());
let limit_insn = limit_reg.map(|_| program.emit_placeholder());
program.emit_insn(Insn::NextAsync { cursor_id });
program.emit_insn(Insn::NextAwait {
cursor_id,
pc_if_next: rewind_await_offset,
});
limit_decr_insn
limit_insn
};
program.fixup_insn(
rewind_await_offset,
@@ -176,9 +184,9 @@ fn translate_select(select: Select) -> Result<Program> {
pc_if_empty: program.offset(),
},
);
limit_decr_insn
limit_insn
}
None => {
(_, None) => {
assert!(!select.exist_aggregation);
let (register_start, register_end) = translate_columns(&mut program, None, &select);
program.emit_insn(Insn::ResultRow {
@@ -188,16 +196,20 @@ fn translate_select(select: Select) -> Result<Program> {
limit_reg.map(|_| program.emit_placeholder())
}
};
if let Some(limit_decr_insn) = limit_decr_insn {
program.fixup_insn(
limit_decr_insn,
Insn::DecrJumpZero {
reg: limit_reg.unwrap(),
target_pc: program.offset(),
},
);
}
program.emit_insn(Insn::Halt);
let halt_offset = program.offset() - 1;
if let Some(limit_insn) = limit_insn {
let insn = match parsed_limit {
Some(0) => Insn::Goto {
target_pc: halt_offset,
},
_ => Insn::DecrJumpZero {
reg: limit_reg.unwrap(),
target_pc: halt_offset,
},
};
program.fixup_insn(limit_insn, insn);
}
program.fixup_insn(
init_offset,
Insn::Init {