feat: add AND rewriter to drop some unnecessary predicates

Signed-off-by: Manan Gupta <[email protected]>

go/vt/vtgate/planbuilder/testdata/postprocess_cases.json

@@ -88,7 +88,7 @@
               "Sharded": true
             },
             "FieldQuery": "select `user`.col1 as a, `user`.col2 from `user` where 1 != 1",
-            "Query": "select `user`.col1 as a, `user`.col2 from `user` where `user`.col1 = 1 and `user`.col1 = `user`.col2 and 1 = 1",
+            "Query": "select `user`.col1 as a, `user`.col2 from `user` where `user`.col1 = 1 and `user`.col1 = `user`.col2",
             "Table": "`user`"
           },
           {
@@ -99,7 +99,7 @@
               "Sharded": true
             },
             "FieldQuery": "select user_extra.col3 from user_extra where 1 != 1",
-            "Query": "select user_extra.col3 from user_extra where user_extra.col3 = 1 and 1 = 1",
+            "Query": "select user_extra.col3 from user_extra where user_extra.col3 = 1",
             "Table": "user_extra"
           }
         ]

go/vt/vtgate/semantics/early_rewriter.go

@@ -47,6 +47,8 @@ func (r *earlyRewriter) down(cursor *sqlparser.Cursor) error {
 		handleOrderBy(r, cursor, node)
 	case *sqlparser.OrExpr:
 		rewriteOrExpr(cursor, node)
+	case *sqlparser.AndExpr:
+		rewriteAndExpr(cursor, node)
 	case *sqlparser.NotExpr:
 		rewriteNotExpr(cursor, node)
 	case sqlparser.GroupBy:
@@ -138,6 +140,45 @@ func rewriteOrExpr(cursor *sqlparser.Cursor, node *sqlparser.OrExpr) {
 	}
 }
 
+// rewriteAndExpr rewrites AND expressions when either side is TRUE.
+func rewriteAndExpr(cursor *sqlparser.Cursor, node *sqlparser.AndExpr) {
+	newNode := rewriteAndTrue(*node)
+	if newNode != nil {
+		cursor.ReplaceAndRevisit(newNode)
+	}
+}
+
+func rewriteAndTrue(andExpr sqlparser.AndExpr) sqlparser.Expr {
+	// we are looking for the pattern `WHERE c = 1 AND 1 = 1`
+	isTrue := func(subExpr sqlparser.Expr) bool {
+		evalEnginePred, err := evalengine.Translate(subExpr, nil)
+		if err != nil {
+			return false
+		}
+
+		env := evalengine.EmptyExpressionEnv()
+		res, err := env.Evaluate(evalEnginePred)
+		if err != nil {
+			return false
+		}
+
+		boolValue, err := res.Value(collations.Default()).ToBool()
+		if err != nil {
+			return false
+		}
+
+		return boolValue
+	}
+
+	if isTrue(andExpr.Left) {
+		return andExpr.Right
+	} else if isTrue(andExpr.Right) {
+		return andExpr.Left
+	}
+
+	return nil
+}
+
 // handleLiteral processes literals within the context of ORDER BY expressions.
 func handleLiteral(r *earlyRewriter, cursor *sqlparser.Cursor, node *sqlparser.Literal) error {
 	newNode, err := r.rewriteOrderByExpr(node)