Name user placed highest number orders

Find the name of the user who has placed the highest number of orders.

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Database schema

CREATE TABLE "public"."product" (
    "product_id" varchar(25) NOT NULL,
    "category_id" varchar(20) NOT NULL,
    "product_name" varchar(255) NOT NULL,
    "price" int4 NOT NULL,
    "quantity" int4 NOT NULL,
    PRIMARY KEY ("product_id")
);

CREATE TABLE "public"."payment" (
    "payment_id" varchar(20) NOT NULL,
    "user_id" varchar(20) NOT NULL,
    "order_id" varchar(20) NOT NULL,
    "payment_date" date NOT NULL,
    "amount" float8 NOT NULL,
    "payment_method" varchar(255) NOT NULL,
    PRIMARY KEY ("payment_id")
);

CREATE TABLE "public"."categories" (
    "category_id" varchar(20) NOT NULL,
    "category_name" varchar(255) NOT NULL,
    PRIMARY KEY ("category_id")
);

CREATE TABLE "public"."reviews" (
    "review_id" varchar(20) NOT NULL,
    "product_id" varchar(20) NOT NULL,
    "user_id" varchar(20) NOT NULL,
    "rating" int4 NOT NULL,
    PRIMARY KEY ("review_id")
);

CREATE TABLE "public"."users" (
    "user_id" varchar(20) NOT NULL,
    "user_name" varchar(255) NOT NULL,
    "email" varchar(255) NOT NULL,
    "mobile_no" varchar(20) NOT NULL,
    "billing_address" varchar(255) NOT NULL,
    PRIMARY KEY ("user_id")
);

CREATE TABLE "public"."address" (
    "user_id" varchar(20) NOT NULL,
    "street_address" varchar(255) NOT NULL,
    "city" varchar(255) NOT NULL,
    "state" varchar(255) NOT NULL,
    "pin_code" int4 NOT NULL,
    "country" varchar(255) NOT NULL,
    PRIMARY KEY ("user_id")
);

CREATE TABLE "public"."orders" (
    "order_id" varchar(20) NOT NULL,
    "product_id" varchar(20) NOT NULL,
    "user_id" varchar(20) NOT NULL,
    "quantity" int4 NOT NULL,
    "date_ordered" date NOT NULL,
    PRIMARY KEY ("order_id")
);