diff --git a/initialize.sql b/initialize.sql
index 5a54a7f..292c50b 100644
--- a/initialize.sql
+++ b/initialize.sql
@@ -76,7 +76,7 @@ CREATE TABLE IF NOT EXISTS tag_space(
 	id          INTEGER NOT NULL,
 	name        TEXT NOT NULL,
 	description TEXT,
-	CHECK (name NOT LIKE '%:%'),
+	CHECK (name NOT LIKE '%:%' AND name NOT LIKE '-%'),
 	PRIMARY KEY (id)
 ) STRICT;
 
diff --git a/main.go b/main.go
index 7c9aceb..644d2d4 100644
--- a/main.go
+++ b/main.go
@@ -62,10 +62,33 @@ func hammingDistance(a, b int64) int {
 	return bits.OnesCount64(uint64(a) ^ uint64(b))
 }
 
+type productAggregator float64
+
+func (pa *productAggregator) Step(v float64) {
+	*pa = productAggregator(float64(*pa) * v)
+}
+
+func (pa *productAggregator) Done() float64 {
+	return float64(*pa)
+}
+
+func newProductAggregator() *productAggregator {
+	pa := productAggregator(1)
+	return &pa
+}
+
 func init() {
 	sql.Register("sqlite3_custom", &sqlite3.SQLiteDriver{
 		ConnectHook: func(conn *sqlite3.SQLiteConn) error {
-			return conn.RegisterFunc("hamming", hammingDistance, true /*pure*/)
+			if err := conn.RegisterFunc(
+				"hamming", hammingDistance, true /*pure*/); err != nil {
+				return err
+			}
+			if err := conn.RegisterAggregator(
+				"product", newProductAggregator, true /*pure*/); err != nil {
+				return err
+			}
+			return nil
 		},
 	})
 }
@@ -956,17 +979,89 @@ func handleAPISimilar(w http.ResponseWriter, r *http.Request) {
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+// This is the most miserable part of the whole program.
 
-// NOTE: AND will mean MULTIPLY(IFNULL(ta.weight, 0)) per SHA1.
-const searchCTE = `WITH
+const searchCTE1 = `WITH
 	matches(sha1, thumbw, thumbh, score) AS (
 		SELECT i.sha1, i.thumbw, i.thumbh, ta.weight AS score
 		FROM tag_assignment AS ta
 		JOIN image AS i ON i.sha1 = ta.sha1
-		WHERE ta.tag = ?
+		WHERE ta.tag = %d
 	)
 `
 
+const searchCTEMulti = `WITH
+	positive(tag) AS (VALUES %s),
+	candidates(sha1) AS (%s),
+	matches(sha1, thumbw, thumbh, score) AS (
+		SELECT i.sha1, i.thumbw, i.thumbh,
+			product(IFNULL(ta.weight, 0)) AS score
+		FROM image AS i, positive AS p
+		JOIN candidates AS c ON i.sha1 = c.sha1
+		LEFT JOIN tag_assignment AS ta ON ta.sha1 = i.sha1 AND ta.tag = p.tag
+		GROUP BY i.sha1
+	)
+`
+
+func parseQuery(query string) (string, error) {
+	positive, negative := []int64{}, []int64{}
+	for _, word := range strings.Split(query, " ") {
+		if word == "" {
+			continue
+		}
+
+		space, tag, _ := strings.Cut(word, ":")
+
+		negated := false
+		if strings.HasPrefix(space, "-") {
+			space = space[1:]
+			negated = true
+		}
+
+		var tagID int64
+		err := db.QueryRow(`
+			SELECT t.id FROM tag AS t
+			JOIN tag_space AS ts ON t.space = ts.id
+			WHERE ts.name = ? AND t.name = ?`, space, tag).Scan(&tagID)
+		if err != nil {
+			return "", err
+		}
+
+		if negated {
+			negative = append(negative, tagID)
+		} else {
+			positive = append(positive, tagID)
+		}
+	}
+
+	// Don't return most of the database, and simplify the following builder.
+	if len(positive) == 0 {
+		return "", errors.New("search is too wide")
+	}
+
+	// Optimise single tag searches.
+	if len(positive) == 1 && len(negative) == 0 {
+		return fmt.Sprintf(searchCTE1, positive[0]), nil
+	}
+
+	values := fmt.Sprintf(`(%d)`, positive[0])
+	candidates := fmt.Sprintf(
+		`SELECT sha1 FROM tag_assignment WHERE tag = %d`, positive[0])
+	for _, tagID := range positive[1:] {
+		values += fmt.Sprintf(`, (%d)`, tagID)
+		candidates += fmt.Sprintf(` INTERSECT
+			SELECT sha1 FROM tag_assignment WHERE tag = %d`, tagID)
+	}
+	for _, tagID := range negative {
+		candidates += fmt.Sprintf(` EXCEPT
+			SELECT sha1 FROM tag_assignment WHERE tag = %d`, tagID)
+	}
+
+	return fmt.Sprintf(searchCTEMulti, values, candidates), nil
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
 type webTagMatch struct {
 	SHA1   string  `json:"sha1"`
 	ThumbW int64   `json:"thumbW"`
@@ -974,10 +1069,10 @@ type webTagMatch struct {
 	Score  float32 `json:"score"`
 }
 
-func getTagMatches(tag int64) (matches []webTagMatch, err error) {
-	rows, err := db.Query(searchCTE+`
+func getTagMatches(cte string) (matches []webTagMatch, err error) {
+	rows, err := db.Query(cte + `
 		SELECT sha1, IFNULL(thumbw, 0), IFNULL(thumbh, 0), score
-		FROM matches`, tag)
+		FROM matches`)
 	if err != nil {
 		return nil, err
 	}
@@ -1001,13 +1096,13 @@ type webTagSupertag struct {
 	score float32
 }
 
-func getTagSupertags(tag int64) (result map[int64]*webTagSupertag, err error) {
-	rows, err := db.Query(searchCTE+`
+func getTagSupertags(cte string) (result map[int64]*webTagSupertag, err error) {
+	rows, err := db.Query(cte + `
 		SELECT DISTINCT ta.tag, ts.name, t.name
 		FROM tag_assignment AS ta
 		JOIN matches AS m ON m.sha1 = ta.sha1
 		JOIN tag AS t ON ta.tag = t.id
-		JOIN tag_space AS ts ON ts.id = t.space`, tag)
+		JOIN tag_space AS ts ON ts.id = t.space`)
 	if err != nil {
 		return nil, err
 	}
@@ -1032,18 +1127,18 @@ type webTagRelated struct {
 	Score float32 `json:"score"`
 }
 
-func getTagRelated(tag int64, matches int) (
+func getTagRelated(cte string, matches int) (
 	result map[string][]webTagRelated, err error) {
 	// Not sure if this level of efficiency is achievable directly in SQL.
-	supertags, err := getTagSupertags(tag)
+	supertags, err := getTagSupertags(cte)
 	if err != nil {
 		return nil, err
 	}
 
-	rows, err := db.Query(searchCTE+`
+	rows, err := db.Query(cte + `
 		SELECT ta.tag, ta.weight
 		FROM tag_assignment AS ta
-		JOIN matches AS m ON m.sha1 = ta.sha1`, tag)
+		JOIN matches AS m ON m.sha1 = ta.sha1`)
 	if err != nil {
 		return nil, err
 	}
@@ -1084,13 +1179,7 @@ func handleAPISearch(w http.ResponseWriter, r *http.Request) {
 		Related map[string][]webTagRelated `json:"related"`
 	}
 
-	space, tag, _ := strings.Cut(params.Query, ":")
-
-	var tagID int64
-	err := db.QueryRow(`
-		SELECT t.id FROM tag AS t
-		JOIN tag_space AS ts ON t.space = ts.id
-		WHERE ts.name = ? AND t.name = ?`, space, tag).Scan(&tagID)
+	cte, err := parseQuery(params.Query)
 	if errors.Is(err, sql.ErrNoRows) {
 		http.Error(w, err.Error(), http.StatusNotFound)
 		return
@@ -1099,11 +1188,11 @@ func handleAPISearch(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if result.Matches, err = getTagMatches(tagID); err != nil {
+	if result.Matches, err = getTagMatches(cte); err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
-	if result.Related, err = getTagRelated(tagID,
+	if result.Related, err = getTagRelated(cte,
 		len(result.Matches)); err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
diff --git a/public/gallery.js b/public/gallery.js
index 9d3b067..01439f7 100644
--- a/public/gallery.js
+++ b/public/gallery.js
@@ -646,7 +646,11 @@ let Search = {
 			m(Header),
 			m('.body', {}, [
 				m('.sidebar', [
-					m('p', SearchModel.query),
+					m('input', {
+						value: SearchModel.query,
+						onchange: event => m.route.set(
+							`/search/:key`, {key: event.target.value}),
+					}),
 					m(SearchRelated),
 				]),
 				m(SearchView),
diff --git a/public/style.css b/public/style.css
index 1bdeb3f..7fd0079 100644
--- a/public/style.css
+++ b/public/style.css
@@ -27,6 +27,8 @@ a { color: inherit; }
 .sidebar { padding: .25rem .5rem; background: var(--shade-color);
 	border-right: 1px solid #ccc; overflow: auto;
 	min-width: 10rem; max-width: 20rem; flex-shrink: 0; }
+.sidebar input { width: 100%; box-sizing: border-box; margin: .5rem 0;
+	font-size: inherit; }
 .sidebar h2 { margin: 0.5em 0 0.25em 0; padding: 0; font-size: 1.2rem; }
 .sidebar ul { margin: .5rem 0; padding: 0; }