fix(chsql): properly handle column aliasing

internal/chstorage/chsql/_golden/Test5.sql

@@ -0,0 +1 @@
+SELECT (toString(name) AS name) FROM spans

internal/chstorage/chsql/_golden/Test6.sql

@@ -0,0 +1 @@
+SELECT (column AS name) FROM spans

internal/chstorage/chsql/_golden/Test7.sql

@@ -0,0 +1 @@
+SELECT (column) FROM spans

internal/chstorage/chsql/select.go

@@ -119,14 +119,15 @@ func (q *SelectQuery) WriteSQL(p *Printer) error {
 		if i != 0 {
 			p.Comma()
 		}
+
 		cexpr := c.Expr
 		if cexpr.IsZero() {
+			// If expression is not defined, assume that column
+			// name is expected.
 			cexpr = Ident(c.Name)
 		}
-		if needColumnAlias(c.Name, cexpr) {
-			// Do not alias the name if name is explicitly aliased by user.
-			cexpr = binaryOp(cexpr, "AS", Ident(c.Name))
-		}
+		cexpr = aliasColumn(c.Name, cexpr)
+
 		p.OpenParen()
 		if err := p.WriteExpr(cexpr); err != nil {
 			return errors.Wrapf(err, "column %q", c.Name)
@@ -188,15 +189,21 @@ func (q *SelectQuery) WriteSQL(p *Printer) error {
 	return nil
 }
 
-func needColumnAlias(name string, cexpr Expr) bool {
-	switch cexpr.typ {
-	case exprBinaryOp:
-		return !strings.EqualFold(cexpr.tok, "AS")
-	case exprIdent:
-		return cexpr.tok != name
-	default:
-		return true
+func aliasColumn(name string, cexpr Expr) Expr {
+	if cexpr.typ == exprBinaryOp && strings.EqualFold(cexpr.tok, "AS") {
+		// If expression already aliased, rename the alias.
+		if len(cexpr.args) < 2 {
+			// Return invalid expression as-is.
+			return cexpr
+		}
+		cexpr = cexpr.args[0]
+	}
+	if cexpr.typ == exprIdent && cexpr.tok == name {
+		// Do not alias expression if it is an identifier (column name)
+		// with same name.
+		return cexpr
 	}
+	return binaryOp(cexpr, "AS", Ident(name))
 }
 
 // ResultColumn defines a column result.

internal/chstorage/chsql/select_test.go

@@ -64,6 +64,7 @@ func TestSelect(t *testing.T) {
 			},
 			false,
 		},
+		// Test subqueries.
 		{
 			func() *SelectQuery {
 				return SelectFrom(
@@ -81,6 +82,7 @@ func TestSelect(t *testing.T) {
 			},
 			false,
 		},
+		// Test ORDER By.
 		{
 			func() *SelectQuery {
 				return Select("spans",
@@ -106,6 +108,46 @@ func TestSelect(t *testing.T) {
 			},
 			false,
 		},
+		// Ensure aliasing is properly handled.
+		//
+		// Alias expression.
+		{
+			func() *SelectQuery {
+				return Select("spans", ResultColumn{
+					Name: "name",
+					Expr: ToString(Ident("name")),
+				})
+			},
+			false,
+		},
+		// User-defined alias.
+		{
+			func() *SelectQuery {
+				return Select("spans", ResultColumn{
+					Name: "name",
+					Expr: binaryOp(
+						Ident("column"),
+						"AS",
+						Ident("spanName"),
+					),
+				})
+			},
+			false,
+		},
+		// User-defined alias with the same name as column.
+		{
+			func() *SelectQuery {
+				return Select("spans", ResultColumn{
+					Name: "column",
+					Expr: binaryOp(
+						Ident("column"),
+						"AS",
+						Ident("spanName"),
+					),
+				})
+			},
+			false,
+		},
 
 		// No columns.
 		{

internal/chstorage/chsql/sugar_test.go

@@ -34,18 +34,17 @@ func TestInTimeRange(t *testing.T) {
 
 func TestJoinAnd(t *testing.T) {
 	tests := []struct {
-		args    []Expr
-		want    string
-		wantErr bool
+		args []Expr
+		want string
 	}{
-		{nil, "true", false},
+		{nil, "true"},
+		{[]Expr{Ident("foo")}, "foo"},
 		{
 			[]Expr{
 				Ident("foo"),
 				Ident("bar"),
 			},
 			"foo AND bar",
-			false,
 		},
 		{
 			[]Expr{
@@ -54,10 +53,7 @@ func TestJoinAnd(t *testing.T) {
 				Ident("baz"),
 			},
 			"foo AND bar AND baz",
-			false,
 		},
-
-		{[]Expr{Ident("foo")}, "", true},
 	}
 	for i, tt := range tests {
 		tt := tt
@@ -66,10 +62,6 @@ func TestJoinAnd(t *testing.T) {
 
 			p := GetPrinter()
 			err := p.WriteExpr(got)
-			if tt.wantErr {
-				require.Error(t, err)
-				return
-			}
 			require.NoError(t, err)
 			require.Equal(t, tt.want, p.String())
 		})