Oracle两表比较查询实现细节分析（oracle两表比较查询）

Introduction

Oracle Database provides a variety of features for managing data, including tables and queries. When working with tables, it is often necessary to compare data between two tables to identify differences or similarities. In this article, we will explore the implementation detls of comparing two tables in Oracle Database.

Comparing Two Tables in Oracle

To compare two tables in Oracle Database, we can use the MINUS operator in a SELECT statement. The MINUS operator returns all distinct rows from the first SELECT statement that are not in the second SELECT statement. For example, consider the following two tables:

Table 1:

ID | Name | Age
---|------|---
1  | John | 28
2  | Mary | 33
3  | Jane | 25
4  | Mark | 31

Table 2:

ID | Name | Age
---|------|---
1  | John | 28
2  | Mary | 30
3  | Jane | 25

To compare the two tables, we can use the following SQL statement:

SELECT *
FROM table1
MINUS
SELECT *
FROM table2;

This will return the following result:

ID | Name | Age
---|------|---
2  | Mary | 33
4  | Mark | 31

This result indicates that there are two rows in Table 1 that are not in Table 2. The first row is for Mark, whose age is 31. The second row is for Mary, whose age is 33.

Comparing Two Tables with Different Column Names

If the two tables being compared have different column names, we can use the AS keyword to alias the column names in the SELECT statements. For example, consider the following two tables:

Table A:

ID | Name | Age
---|------|---
1  | John | 28
2  | Mary | 33
3  | Jane | 25
4  | Mark | 31

Table B:

CustomerID | FullName | yrsOld
-----------|----------|-------
1          | John     | 28
2          | Mary     | 30
3          | Jane     | 25

To compare these two tables, we can alias the column names in the following SQL statement:

SELECT ID, Name, Age
FROM A
MINUS
SELECT CustomerID AS ID, FullName AS Name, yrsOld AS Age
FROM B;

This will return the same result as before, indicating that there are two rows in Table A that are not in Table B.

Conclusion

Comparing two tables in Oracle Database is a powerful feature that can help identify differences or similarities between data sets. By using the MINUS operator in a SELECT statement, we can easily compare the contents of two tables. Furthermore, by aliasing column names with the AS keyword, we can compare tables with different column names.