在这个例子中，WITH 语句做了什么？我正在尝试随机生成数据

发布于 2024-08-04 17:31:22 字数 285 浏览 7 评论 0原文

INSERT INTO files (fileUID, filename)
WITH fileUIDS(fileUID) AS
( VALUES(1) UNION ALL
  SELECT fileUID+1 FROM fileUIDS WHERE fileUID < 1000 )
SELECT fileUID,
       TRANSLATE ( CHAR(BIGINT(RAND() * 10000000000 )), 'abcdefgHij', '1234567890' )
FROM fileUIDS;

原文

INSERT INTO files (fileUID, filename)
WITH fileUIDS(fileUID) AS
( VALUES(1) UNION ALL
  SELECT fileUID+1 FROM fileUIDS WHERE fileUID < 1000 )
SELECT fileUID,
       TRANSLATE ( CHAR(BIGINT(RAND() * 10000000000 )), 'abcdefgHij', '1234567890' )
FROM fileUIDS;

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人疚 2024-08-11 17:31:22

WITH 语法与使用本地临时表或内联视图相同。据我所知，它仅在 SQL Server（2005+，称为通用表表达式）和 Oracle（9i+，称为子查询分解）中受支持。预期用途是创建在单个查询中多次使用（即连接）的基本视图。

这是一个典型的示例：

WITH example AS (
     SELECT q.question_id,
            t.tag_name
       FROM QUESTIONS q
       JOIN QUESTION_TAG_XREF qtf ON qtf.question_id = t.question_id
       JOIN TAGS t ON t.tag_id = qtf.tag_id)
SELECT t.title,
       e1.tag_name
  FROM QUESTIONS t
  JOIN example e1 ON e1.question_id = t.question_id

...如果您使用以下命令，它将返回相同的结果：

SELECT t.title,
       e1.tag_name
  FROM QUESTIONS t
  JOIN (SELECT q.question_id,
               t.tag_name
          FROM QUESTIONS q
          JOIN QUESTION_TAG_XREF qtf ON qtf.question_id = t.question_id
          JOIN TAGS t ON t.tag_id = qtf.tag_id) e1 ON e1.question_id = t.question_id

您提供的示例：

WITH fileUIDS(fileUID) AS ( 
     VALUES(1) 
     UNION ALL
     SELECT t.fileUID+1 
       FROM fileUIDS t
      WHERE t.fileUID < 1000 )
INSERT INTO files 
    (fileUID, filename)
SELECT f.fileUID,
       TRANSLATE ( CHAR(BIGINT(RAND() * 10000000000 )), 'abcdefgHij', '1234567890' )
  FROM fileUIDS f;

...是一个递归示例。它从 1 开始，总共生成 999 个 fileuid（如果从 0 开始，则生成 1,000 个）。

The WITH syntax is the same as using either a local temp table or inline view. To my knowledge, it's only supported in SQL Server (2005+, called Common Table Expressions) and Oracle (9i+, called Subquery Factoring). The intended use is for creating a basic view that is used (ie: joined to) multiple times in a single query.

Here's a typical example:

WITH example AS (
     SELECT q.question_id,
            t.tag_name
       FROM QUESTIONS q
       JOIN QUESTION_TAG_XREF qtf ON qtf.question_id = t.question_id
       JOIN TAGS t ON t.tag_id = qtf.tag_id)
SELECT t.title,
       e1.tag_name
  FROM QUESTIONS t
  JOIN example e1 ON e1.question_id = t.question_id

...which will return identical results if you use:

SELECT t.title,
       e1.tag_name
  FROM QUESTIONS t
  JOIN (SELECT q.question_id,
               t.tag_name
          FROM QUESTIONS q
          JOIN QUESTION_TAG_XREF qtf ON qtf.question_id = t.question_id
          JOIN TAGS t ON t.tag_id = qtf.tag_id) e1 ON e1.question_id = t.question_id

The example you provided:

WITH fileUIDS(fileUID) AS ( 
     VALUES(1) 
     UNION ALL
     SELECT t.fileUID+1 
       FROM fileUIDS t
      WHERE t.fileUID < 1000 )
INSERT INTO files 
    (fileUID, filename)
SELECT f.fileUID,
       TRANSLATE ( CHAR(BIGINT(RAND() * 10000000000 )), 'abcdefgHij', '1234567890' )
  FROM fileUIDS f;

...is a recursive one. It's starting at 1, generating 999 fileuids in total (it would be 1,000 if it had started at 0).

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