Fix SQL syntax error for mixed named columns and * in SELECT

Dolt was incorrectly allowing queries like `SELECT 'parent' as db, * FROM table`
which MySQL rejects with a syntax error. This implements MySQL's rule that
named expressions cannot appear before unqualified * in SELECT clauses.

The fix:
- Validates SELECT expressions in the existing processing loop
- Rejects named expressions before unqualified * (matches MySQL behavior)
- Allows qualified table.* in any position
- Allows expressions after * (e.g., SELECT *, column)

Fixes dolthub/dolt#9519

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: elianddb

sql/planbuilder/parse_test.go

@@ -2969,6 +2969,24 @@ func TestPlanBuilderErr(t *testing.T) {
 			Query: "select 1 from xy group by 100;",
 			Err:   "column ordinal out of range: 100",
 		},
+		
+		// Test mixed named columns and star expressions
+		{
+			Query: "SELECT x, * FROM xy",
+			Err:   "Invalid syntax: cannot mix named columns with '*' in SELECT clause",
+		},
+		{
+			Query: "SELECT 'constant', * FROM xy",
+			Err:   "Invalid syntax: cannot mix named columns with '*' in SELECT clause",
+		},
+		{
+			Query: "SELECT 1, * FROM xy",
+			Err:   "Invalid syntax: cannot mix named columns with '*' in SELECT clause",
+		},
+		{
+			Query: "SELECT * FROM (SELECT 'parent' as db, * FROM xy) as combined",
+			Err:   "Invalid syntax: cannot mix named columns with '*' in SELECT clause",
+		},
 	}
 
 	db := memory.NewDatabase("mydb")

sql/planbuilder/project.go

@@ -41,7 +41,16 @@ func (b *Builder) analyzeSelectList(inScope, outScope *scope, selectExprs ast.Se
 
 	// need to transfer aggregation state from out -> in
 	var exprs []sql.Expression
+	var hasColumnBeforeStar bool
 	for _, se := range selectExprs {
+		// Check for named expressions before unqualified *
+		if star, ok := se.(*ast.StarExpr); ok {
+			if star.TableName.IsEmpty() && hasColumnBeforeStar {
+				b.handleErr(sql.ErrInvalidSyntax.New("cannot mix named columns with '*' in SELECT clause"))
+			}
+		} else if _, ok := se.(*ast.AliasedExpr); ok {
+			hasColumnBeforeStar = true
+		}
 		pe := b.selectExprToExpression(inScope, se)
 
 		// TODO two passes for symbol res and semantic validation