Support schema.table.column syntax in expressions

[Copilot]

• Understand the codebase structure and issue
• Modify AST to support schema in QualifiedRef
• Update parseQualifiedRef to parse three-part identifiers
• Add tests for schema.table.column expressions
• Verify the fix works with the provided example
• Run existing tests to ensure no regressions
• Run code review
• Run security checks
• Run go fmt on all files

Summary

Successfully fixed the parser to support schema.table.column format in expressions, which is valid SQLite syntax.

Changes Made:

1. AST (ast.go): Added Schema and SchemaPos fields to QualifiedRef structure
2. Parser (parser.go): Updated parseQualifiedRef to detect and handle three-part identifiers
3. Tests (parser_test.go): Added comprehensive tests for three-part identifiers
4. Walk (walk.go): Updated to traverse the new Schema field
5. Formatting: Applied go fmt to ensure proper code formatting

Test Results:

• ✅ All existing tests pass
• ✅ New tests for three-part identifiers pass
• ✅ Original failing query now parses correctly: UPDATE main.vals SET a=lower(main.vals.a)
• ✅ Code review completed (2 false positives)
• ✅ Security scan completed (0 issues)
• ✅ Code properly formatted with go fmt

Backward Compatibility:

• Two-part identifiers (table.column) continue to work as before
• New three-part identifiers (schema.table.column) now work correctly

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Parse failures of schema.table.column in expressions</issue_title>
<issue_description>SQLite allows us to refer to a table with its schema even in expressions. For example:

sqlite> SELECT * FROM Vals;
+---+
| A |
+---+
| a |
| b |
| c |
| d |
| e |
+---+
sqlite> UPDATE main.vals SET a=upper(main.vals.a);
sqlite> SELECT * FROM vals;
+---+
| A |
+---+
| A |
| B |
| C |
| D |
| E |
+---+

But the following query fails to parse: https://go.dev/play/p/sL9Q2UYtJxT

package main

import (
	"fmt"
	"strings"

	"github.com/rqlite/sql"
)

func main() {
	for _, q := range []string{
		`UPDATE main.vals SET a=lower(main.vals.a)`,
	} {
		p := sql.NewParser(strings.NewReader(q))
		s, err := p.ParseStatement()
		fmt.Printf("%q\n   err: %v\n  stmt: %#v\n", q, err, s)
	}
}

produces:

"UPDATE main.vals SET a=lower(main.vals.a)"
   err: 1:39: expected comma or right paren, found '.'
  stmt: &sql.UpdateStatement{WithClause:(*sql.WithClause)(nil), Update:sql.Pos{Offset:0, Line:1, Column:1}, UpdateOr:sql.Pos{Offset:0, Line:0, Column:0}, UpdateOrReplace:sql.Pos{Offset:0, Line:0, Column:0}, UpdateOrRollback:sql.Pos{Offset:0, Line:0, Column:0}, UpdateOrAbort:sql.Pos{Offset:0, Line:0, Column:0}, UpdateOrFail:sql.Pos{Offset:0, Line:0, Column:0}, UpdateOrIgnore:sql.Pos{Offset:0, Line:0, Column:0}, Table:(*sql.QualifiedTableName)(0xc0000a4000), Set:sql.Pos{Offset:17, Line:1, Column:18}, Assignments:[]*sql.Assignment(nil), Where:sql.Pos{Offset:0, Line:0, Column:0}, WhereExpr:sql.Expr(nil), ReturningClause:(*sql.ReturningClause)(nil)}
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Parse failures of schema.table.column in expressions #101

---

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[otoolep]

@copilot -- 'go fmt' your code.

[Copilot]

@copilot -- 'go fmt' your code.

Done in commit 1023153. Removed trailing whitespace from parser.go.

[icio]

Looks good to me. Thanks for responding to all of these issues, @otoolep :)