mysql - Oracle - 尝试在同一查询中查询两个表中的数据

Question

我尝试主要从一个表查询数据，但我还需要同一数据库中另一个表的两列。我的查询的一部分看起来有点像这样:

SELECT
      'Contact 1' AS "Phone 2 - Type",
      Emerg_Phone_1 AS "Phone 2 - Value",
      'Contact 2' AS "Phone 3 - Type",
      Emerg_Phone_2 AS "Phone 3 - Value",
      'Student Cell' AS "Phone 4 - Type",
      STUDENTCELL AS "Phone 4 - Value",
FROM STUDENTS JOIN STUDENTS2

所以基本上，除了 STUDENTCELL 之外的所有五个选择都来自 STUDENTS 表，但我需要在同一查询中使用 STUDENTS2 表中的一列 STUDENTCELL。感谢您的帮助和建议，我对 mySQL 和 oracle 都很陌生。

Answer 1

你几乎得到了解决方案。除了连接子句之外。您需要使用公共(public)列连接两个表。因此，您可以使用 ON 子句 或 Using 子句。 这两者的基本区别是

USING 子句

The USING clause is used if several columns share the same name but you don’t want to join using all of these common columns. The columns listed in the USING clause can’t have any qualifiers in the statement, including the WHERE clause:

ON 子句

The ON clause is used to join tables where the column names don’t match in both tables. The join conditions are removed from the filter conditions in the WHERE clause:

我正在将 Common 列视为 ID。如果两个表具有不同的列名，则使用 on

SELECT
      'Contact 1' AS "Phone 2 - Type",
      Emerg_Phone_1 AS "Phone 2 - Value",
      'Contact 2' AS "Phone 3 - Type",
      Emerg_Phone_2 AS "Phone 3 - Value",
      'Student Cell' AS "Phone 4 - Type",
      STUDENTCELL AS "Phone 4 - Value",
FROM STUDENTS JOIN STUDENTS2 ON (STUDENTS.Stud_ID=STUDENTS2.Stud2_ID)

如果两个表具有相同的列名，则使用using

SELECT
      'Contact 1' AS "Phone 2 - Type",
      Emerg_Phone_1 AS "Phone 2 - Value",
      'Contact 2' AS "Phone 3 - Type",
      Emerg_Phone_2 AS "Phone 3 - Value",
      'Student Cell' AS "Phone 4 - Type",
      STUDENTCELL AS "Phone 4 - Value",
FROM STUDENTS JOIN STUDENTS2 using (id);

您可能想浏览Oracle JOINS和 SQL JOINS