Question

这是我的工作查询：

SELECT 
    public."T1"."Id"    AS "StuffId",
    public."T1"."Name"  AS "StuffName",
    public."T3"."Id"    AS "ThingId",
    public."T3"."Name"  AS "ThingName",
    public."T4"."Id"    AS "AnyId",
    public."T4"."Name"  AS "AnyName"
FROM public."T1"
INNER JOIN  public."T2"
    ON public."T1"."Id" = public."T2"."StuffId"
INNER JOIN public."T3"
    ON public."T2"."Id" = public."T2"."ThingId"
INNER JOIN public."T4"
    ON public."T4"."Id" = public."T2"."AnyId"

我想以一种更具可读性的方式使用别名来编写它，但是对于别名，它永远不会被确认。

我很了解Postgresql，但是我对SQL Server，My SQL和Oracle有很好的了解。

这就是我想要的：

SELECT 
    Stuff.Id    AS "StuffId",
    Stuff.Name  AS "StuffName",
    Thing.Id    AS "ThingId",
    Thing.Name  AS "ThingName",
    Any.Id  AS "AnyId",
    Any.Name    AS "AnyName"
FROM public."T1" AS Stuff
INNER JOIN  public."T2" AS Link
    ON Stuff.Id = Link.StuffId
INNER JOIN public."T3" AS Thing
    ON Thing.Id = Link.ThingId
INNER JOIN public."T4" AS Any
    ON Any.Id = Link.AnyId

在第一个查询中应该有什么类似的内容？

Answer 1

您要做的第一件事是摆脱标识符周围所有这些嘈杂的引号。在标准SQL中，标识符被视为不区分大小写（默认为大写），因此这3个（未加引号的）限定符在语法上是等效的：

... as FOO
... as foo
... as FoO

当确实需要混合大小写或标识符与保留关键字冲突时，可以使用带引号的标识符。

用例中的问题是，您不能从查询中删除引号，因为您的表最初是使用（带引号的）camelCase标识符创建的，例如：

CREATE TABLE T1 (
    "Id"    INT,
    "Name"  VARCHAR(100)
);

您需要RENAME these columns到没有引号的内容：

ALTER TABLE T1 RENAME "Id" TO id;
ALTER TABLE T1 RENAME "Name" TO name;

要替换camelCase表示法中的大小写中断，我建议使用下划线字符：

ALTER TABLE T2 RENAME "StuffId" TO stuff_id;

所有表列均正确重命名后，即可运行以下查询：

SELECT 
    Stuff.Id    AS Stuff_Id,
    Stuff.Name  AS Stuff_Name,
    Thing.Id    AS Thing_Id,
    Thing.Name  AS Thing_Name,
    Any.Id      AS Any_Id,
    Any.Name    AS Any_Name
FROM 
    T1 AS Stuff
    INNER JOIN T2 AS Link ON Stuff.Id = Link.Stuff_Id
    INNER JOIN T3 AS Thing ON Thing.Id = Link.Thing_Id
    INNER JOIN T4 AS Any ON Any.Id = Link.Any_Id

Answer 2

单词public是SHEMA的名字。如果这是默认的数据库模式，那么您可能会在查询中错过它。像这样T1.Id这样写就可以了。

如果此模式不是默认模式，那么您可以为某些数据库用户更改它，并与他Change default schema for user一起使用

编写查询的更有效方法

2 个答案: