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Add support for CASE expressions.
There's two forms of case: CASE (WHEN [bool expr] THEN [value])+ (ELSE [value])? END which checks a series of boolean conditions, and: CASE expr (WHEN [expr] THEN [value})+ (ELSE [value])? END Which checks a series of equality conditions. This implements support for both. Note that the ELSE is optional, and will be equivalent to `ELSE null` if not specified. sqlite3 gives the implementation as: sqlite> explain select case a WHEN a THEN b WHEN c THEN d ELSE 0 END from casetest; addr opcode p1 p2 p3 p4 p5 comment ---- ------------- ---- ---- ---- ------------- -- ------------- 0 Init 0 16 0 0 Start at 16 1 OpenRead 0 3 0 4 0 root=3 iDb=0; casetest 2 Rewind 0 15 0 0 3 Column 0 0 2 0 r[2]= cursor 0 column 0 4 Column 0 0 3 0 r[3]= cursor 0 column 0 5 Ne 3 8 2 BINARY-8 83 if r[2]!=r[3] goto 8 6 Column 0 1 1 0 r[1]= cursor 0 column 1 7 Goto 0 13 0 0 8 Column 0 2 3 0 r[3]= cursor 0 column 2 9 Ne 3 12 2 BINARY-8 83 if r[2]!=r[3] goto 12 10 Column 0 3 1 0 r[1]= cursor 0 column 3 11 Goto 0 13 0 0 12 Integer 0 1 0 0 r[1]=0 13 ResultRow 1 1 0 0 output=r[1] 14 Next 0 3 0 1 15 Halt 0 0 0 0 16 Transaction 0 0 2 0 1 usesStmtJournal=0 17 Goto 0 1 0 0 and after this patch, limbo gives: addr opcode p1 p2 p3 p4 p5 comment ---- ----------------- ---- ---- ---- ------------- -- ------- 0 Init 0 18 0 0 Start at 18 1 OpenReadAsync 0 4 0 0 table=casetest, root=4 2 OpenReadAwait 0 0 0 0 3 RewindAsync 0 0 0 0 4 RewindAwait 0 17 0 0 Rewind table casetest 5 Column 0 0 2 0 r[2]=casetest.a 6 Column 0 0 3 0 r[3]=casetest.a 7 Ne 2 3 10 0 if r[2]!=r[3] goto 10 8 Column 0 1 1 0 r[1]=casetest.b 9 Goto 0 14 0 0 10 Column 0 2 3 0 r[3]=casetest.c 11 Ne 2 3 14 0 if r[2]!=r[3] goto 14 12 Column 0 3 1 0 r[1]=casetest.d 13 Goto 0 14 0 0 14 ResultRow 1 1 0 0 output=r[1] 15 NextAsync 0 0 0 0 16 NextAwait 0 5 0 0 17 Halt 0 0 0 0 18 Transaction 0 0 0 0 19 Integer 0 1 0 0 r[1]=0 20 Goto 0 1 0 0 And then as there's nowhere to annotate this new support in COMPAT.md, I added a corresponding heading for SELECT expressions and what is/isn't supported.
This commit is contained in:
Alex Miller
28
COMPAT.md
28
COMPAT.md
@@ -60,6 +60,33 @@ This document describes the SQLite compatibility status of Limbo:
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| VACUUM | No | |
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| WITH clause | No | |
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### SELECT Expressions
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Feature support of [sqlite expr syntax](https://www.sqlite.org/lang_expr.html).
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| Syntax | Status | Comment |
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|------------------------------|---------|---------|
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| literals | Yes | |
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| schema.table.column | Partial | Schemas aren't supported |
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| unary operator | Partial | `-` supported, `+~` aren't |
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| binary operator | Partial | Only `%`, `!<`, and `!>` are unsupported |
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| agg() FILTER (WHERE ...) | No | Is incorrectly ignored |
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| ... OVER (...) | No | Is incorrectly ignored |
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| (expr) | Yes | |
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| CAST (expr AS type) | Yes | |
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| COLLATE | No | |
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| (NOT) LIKE | No | |
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| (NOT) GLOB | No | |
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| (NOT) REGEXP | No | |
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| (NOT) MATCH | No | |
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| IS (NOT) | No | |
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| IS (NOT) DISTINCT FROM | No | |
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| (NOT) BETWEEN ... AND ... | No | |
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| (NOT) IN (subquery) | No | |
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| (NOT) EXISTS (subquery) | No | |
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| CASE WHEN THEN ELSE END | Yes | |
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| RAISE | No | |
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## SQL functions
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### Scalar functions
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@@ -139,7 +166,6 @@ This document describes the SQLite compatibility status of Limbo:
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| sum(X) | Yes | |
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| total(X) | Yes | |
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### Date and time functions
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| Function | Status | Comment |
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@@ -698,7 +698,92 @@ pub fn translate_expr(
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}
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Ok(target_register)
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}
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ast::Expr::Case { .. } => todo!(),
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ast::Expr::Case {
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base,
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when_then_pairs,
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else_expr,
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} => {
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// There's two forms of CASE, one which does quality against the then values:
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// CASE [expr] WHEN [value] ELSE [value] END
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// And one which evaluates a series of boolean predicates:
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// CASE (WHEN [bool_expr] THEN [value])+ END
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let return_label = program.allocate_label();
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let mut next_case_label = program.allocate_label();
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let base_reg = base.as_ref().map(|_| program.alloc_register());
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let expr_reg = program.alloc_register();
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if let Some(base_expr) = base {
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translate_expr(
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program,
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referenced_tables,
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base_expr,
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base_reg.unwrap(),
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precomputed_exprs_to_registers,
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)?;
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};
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for (when_expr, then_expr) in when_then_pairs {
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translate_expr(
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program,
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referenced_tables,
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when_expr,
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expr_reg,
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precomputed_exprs_to_registers,
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)?;
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match base_reg {
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Some(base_reg) => program.emit_insn_with_label_dependency(
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Insn::Ne {
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lhs: base_reg,
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rhs: expr_reg,
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target_pc: next_case_label,
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},
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next_case_label,
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),
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None => program.emit_insn_with_label_dependency(
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Insn::IfNot {
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reg: expr_reg,
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target_pc: next_case_label,
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null_reg: 1,
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},
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next_case_label,
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),
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};
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translate_expr(
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program,
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referenced_tables,
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then_expr,
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target_register,
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precomputed_exprs_to_registers,
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)?;
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program.emit_insn_with_label_dependency(
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Insn::Goto {
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target_pc: return_label,
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},
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return_label,
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);
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program.preassign_label_to_next_insn(next_case_label);
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next_case_label = program.allocate_label();
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}
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match else_expr {
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Some(expr) => {
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translate_expr(
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program,
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referenced_tables,
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expr,
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target_register,
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precomputed_exprs_to_registers,
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)?;
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}
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// If ELSE isn't specified, it means ELSE null
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None => {
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program.emit_insn(Insn::Null {
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dest: target_register,
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dest_end: None,
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});
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}
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};
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program.mark_last_insn_constant();
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program.preassign_label_to_next_insn(return_label);
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Ok(target_register)
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}
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ast::Expr::Cast { expr, type_name } => {
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let type_name = type_name.as_ref().unwrap(); // TODO: why is this optional?
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let reg_expr = program.alloc_register();
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@@ -599,6 +599,7 @@ impl ProgramState {
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}
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}
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#[derive(Debug)]
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pub struct Program {
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pub max_registers: usize,
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pub insns: Vec<Insn>,
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@@ -57,4 +57,20 @@ do_execsql_test seekrowid {
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do_execsql_test select_parenthesized {
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select (price + 100) from products limit 1;
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} {179.0}
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} {179.0}
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do_execsql_test select_case_base_else {
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select case when 0 then 0 when 1 then 1 else 2 end;
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} {1}
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do_execsql_test select_case_noelse_null {
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select case when 0 then 0 end;
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} {}
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do_execsql_test select_base_case_else {
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select case 1 when 0 then 0 when 1 then 1 else 2 end;
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} {1}
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do_execsql_test select_base_case_noelse_null {
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select case 4 when 0 then 0 when 1 then 1 end;
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} {}
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