feat(chsql): add PREWHERE

internal/chstorage/chsql/_golden/Test8.sql

@@ -0,0 +1 @@
+SELECT body FROM logs PREWHERE (hasToken(body, 'Error'))

internal/chstorage/chsql/chsql.go

@@ -204,6 +204,11 @@ func (p *Printer) From() {
 	p.Ident("FROM")
 }
 
+// Prewhere writes `PREWHERE` ident.
+func (p *Printer) Prewhere() {
+	p.Ident("PREWHERE")
+}
+
 // Where writes `WHERE` ident.
 func (p *Printer) Where() {
 	p.Ident("WHERE")

internal/chstorage/chsql/select.go

@@ -18,6 +18,8 @@ type SelectQuery struct {
 	distinct bool
 	columns  []ResultColumn
 
+	// prewhere is a set of expression joined by AND
+	prewhere []Expr
 	// where is a set of expression joined by AND
 	where []Expr
 	order []orderExpr
@@ -54,6 +56,12 @@ func (q *SelectQuery) Distinct(b bool) *SelectQuery {
 	return q
 }
 
+// Prewhere adds filters to query.
+func (q *SelectQuery) Prewhere(filters ...Expr) *SelectQuery {
+	q.prewhere = append(q.prewhere, filters...)
+	return q
+}
+
 // Where adds filters to query.
 func (q *SelectQuery) Where(filters ...Expr) *SelectQuery {
 	q.where = append(q.where, filters...)
@@ -145,6 +153,19 @@ func (q *SelectQuery) WriteSQL(p *Printer) error {
 	default:
 		return errors.New("either table or sub-query must be present")
 	}
+	if len(q.prewhere) > 0 {
+		p.Prewhere()
+		for i, filter := range q.prewhere {
+			if i != 0 {
+				p.And()
+			}
+			p.OpenParen()
+			if err := p.WriteExpr(filter); err != nil {
+				return errors.Wrapf(err, "prewhere %d", i)
+			}
+			p.CloseParen()
+		}
+	}
 	if len(q.where) > 0 {
 		p.Where()
 		for i, filter := range q.where {
@@ -153,7 +174,7 @@ func (q *SelectQuery) WriteSQL(p *Printer) error {
 			}
 			p.OpenParen()
 			if err := p.WriteExpr(filter); err != nil {
-				return errors.Wrapf(err, "filter %d", i)
+				return errors.Wrapf(err, "where %d", i)
 			}
 			p.CloseParen()
 		}

internal/chstorage/chsql/select_test.go

@@ -149,6 +149,20 @@ func TestSelect(t *testing.T) {
 			false,
 		},
 
+		// Test PREWHERE.
+		{
+			func() *SelectQuery {
+				return Select(
+					"logs",
+					Column("body", nil),
+				).
+					Prewhere(
+						HasToken(Ident("body"), "Error"),
+					)
+			},
+			false,
+		},
+
 		// No columns.
 		{
 			func() *SelectQuery { return Select("logs") },