Create plan for Update queries

[PThorpe92]

closes #1186, or at least works towards it by implementing an actual Plan for update queries instead of translating everything inline. This allows for actually using index's, rewriting const expressions, pushing predicates instead of hardcoding a full scan in the translation.

TODOs:

1. RETURNING clause/result columns
2. OFFSET clauses
3. on conflict

LIMIT:

By supporting LIMIT directly in update queries, we'll have to put the tests outside of the compatibility tests, maybe in the CLI tests.

[jussisaurio]

Hi @PThorpe92 , I was testing out this branch locally and found at least the following panic:

limbo> update users set first_name = 'old bastard' where age > 80;

thread 'main' panicked at core/types.rs:513:21:
index out of bounds: the len is 2 but the index is 2

The EXPLAIN for this query also panics so I can't see what the full generated bytecode is 😅

My guess is it's incorrectly trying to get all the columns from the index since it's using age_idx in the WHERE clause

Quick "not very clean code" fix:

diff --git a/core/translate/emitter.rs b/core/translate/emitter.rs
index 9cfb0ac2..2d2a3da8 100644
--- a/core/translate/emitter.rs
+++ b/core/translate/emitter.rs
@@ -469,13 +469,15 @@ fn emit_update_insns(
     program: &mut ProgramBuilder,
 ) -> crate::Result<()> {
     let table_ref = &plan.table_references.first().unwrap();
-    let cursor_id = match &table_ref.op {
-        Operation::Scan { .. } => program.resolve_cursor_id(&table_ref.identifier),
+    let (cursor_id, index) = match &table_ref.op {
+        Operation::Scan { .. } => (program.resolve_cursor_id(&table_ref.identifier), None),
         Operation::Search(search) => match search {
             &Search::RowidEq { .. } | Search::RowidSearch { .. } => {
-                program.resolve_cursor_id(&table_ref.identifier)
+                (program.resolve_cursor_id(&table_ref.identifier), None)
+            }
+            Search::IndexSearch { index, .. } => {
+                (program.resolve_cursor_id(&table_ref.identifier), Some((index.clone(), program.resolve_cursor_id(&index.name))))
             }
-            Search::IndexSearch { index, .. } => program.resolve_cursor_id(&index.name),
         },
         _ => return Ok(()),
     };
@@ -521,9 +523,13 @@ fn emit_update_insns(
                 &t_ctx.resolver,
             )?;
         } else {
+            let table_column = table_ref.table.columns().get(idx).unwrap();
+            let column_idx_in_index = index.as_ref().and_then(|(idx, _)| {
+                idx.columns.iter().position(|c| Some(&c.name) == table_column.name.as_ref())
+            });
             program.emit_insn(Insn::Column {
-                cursor_id,
-                column: idx,
+                cursor_id: *index.as_ref().and_then(|(_, id)| if column_idx_in_index.is_some() { Some(id) } else { None }).unwrap_or(&cursor_id),
+                column: column_idx_in_index.unwrap_or(idx),
                 dest: first_col_reg + idx,
             });
         }

[PThorpe92]

fixed that issue but there is still an issue with doing queries that trigger many updates, e.g. on a copy of the testing/testing.db, doing that example query you gave will end up looping indefinitely.

@krishvishal confirmed that this is likely from a balancing issue, and he has an incoming fix.