Merge Tables from Two SQL Databases

You can merge tables from two databases using the following method:

1. Use the INSERT INTO statement to insert table data from the source database into the table in the destination database. For example:

INSERT INTO 目标数据库.目标表
SELECT * FROM 源数据库.源表;

This will replicate all data from the source table to the target table.

1. You can merge data from two tables into one result set using the UNION or UNION ALL operators if the tables have the same column structure. The UNION operator removes duplicates, while the UNION ALL operator retains duplicate rows. For example:

SELECT * FROM 源数据库.源表
UNION ALL
SELECT * FROM 目标数据库.目标表;

This will return a result set that combines data from two tables.

1. Use multiple INSERT INTO statements: If the structures of two tables are different, you can use multiple INSERT INTO statements to insert data from the source table into the target table, and perform data transformation and mapping as needed. For example:

INSERT INTO 目标数据库.目标表 (目标列1, 目标列2, ...)
SELECT 源列1, 源列2, ...
FROM 源数据库.源表;

It is necessary to ensure that the columns in the target table have the same data type and length as the corresponding columns in the source table.

These methods are applicable to most relational databases, such as MySQL, Oracle, SQL Server, etc. The specific syntax and steps may vary depending on the database being used, so adjustments can be made according to the database system being used.