在字符串中实现每个查询的结果答案

【问题标题】：Realise result of every query in a string在字符串中实现每个查询的结果
【发布时间】：2016-07-18 18:18:32
【问题描述】：

我是 Clojure 的新手，正在开发一个 jdbc 应用程序，其中我有一个字符串，该字符串中定义了三个查询，如下所示。

(def tpch_query15
      (str "create view revenue0 (supplier_no, total_revenue) as select l_suppkey, sum(l_extendedprice * (1 - l_discount)) "
        "from lineitem where l_shipdate >= date '1993-04-01' and l_shipdate < date '1993-04-01' + interval '3' month group by l_suppkey; "
            "select s_suppkey, s_name, s_address, s_phone, total_revenue from supplier, revenue0 where s_suppkey = supplier_no "
        "and total_revenue = (select max(total_revenue) from revenue0) order by s_suppkey LIMIT 1; drop view revenue0"))

(defn run-a-query
  "Run a query three times and return the average time."
  [conn-db query queryno]
  (println (str "Running query " queryno))
  (let [starttime (System/currentTimeMillis)]
    (dotimes [n 3]
      (try
        (let
          [rs (sql/query conn-db query)]
        ;; Print column names with | as delimiter
        (dorun 0 (map #(println (clojure.string/join " | " (keys %))) rs))
        ;; Print a seperator between column names and rows
        (println "------------------------------------------------------")
        ;; Print rows with | as delimiter
        (dorun (map #(println (clojure.string/join " | " (vals %))) rs)))
        (catch Exception e)))
      (/ (- (System/currentTimeMillis) starttime) 3.0)))

;;https://clojuredocs.org/clojure.core/conj!
(defn run-all-queries
  "Run all TPC-H queries. Return a vector of average time taken for each query."
  [conn-db]
  (loop [i 0 v (transient [])]
    (if (< i 22)
      (recur (inc i) (conj! v (run-a-query conn-db (get queries-to-run i) (+ i 1))))
      (persistent! v))))

是否可以让 run-a-query 函数打印该字符串中定义的所有三个查询的结果。目前，当 run-a-query 传递 tpch_query15 时，它不会打印出任何结果。据我了解，这是因为作为下拉视图的三个查询中的最后一个不返回结果集，它只会返回最后一个查询结果。

【问题讨论】：

标签： postgresql jdbc clojure

【解决方案1】：

使用 WITH 子句 (https://www.postgresql.org/docs/current/static/queries-with.html) 将您的查询重新表述为单个 SQL SELECT 语句，而不是创建然后删除视图：

with
  revenue0 (supplier_no, ...) as (select l_suppkey, ... )
select s_suppkey, ...
from supplier, revenue0,...

无论有没有 Clojure、JDBC 等，您都不需要在这里查看视图。无论如何，在同一连接上（尤其是在同一请求中）将 DDL 与查询/DML 混合通常是一个坏主意 -性能可能会受到很大影响，具体取决于数据库、版本、驱动程序等。

【讨论】：