When migrating data to MySQL, you need to pay attention to key links to avoid data loss or structural confusion. First, we sort out the source database structure and check the table structure, field type, index, primary key and character set compatibility, especially encoding problems such as the conversion from GBK to utf8mb4. Secondly, select the appropriate data export tool, such as pg_dump, expdp, or ETL tool, pay attention to special character processing when exporting, use CSV intermediate format and ensure escape rules. Next, use LOAD DATA INFILE or client tools to import data in batches, first create a target table structure, close indexes and foreign keys when large amounts of data to improve efficiency, and record logs to track problems. Finally, verify the consistency of the data, compare the number of records, randomly check the data content, update the statistical information, rebuild the index and foreign keys, and adjust user permissions to ensure security.

When migrating data to MySQL, many people initially thought it was just "storing data in another place", but when they really did it, they found that there were many details that were prone to errors. In fact, this is not difficult, but you must be careful to deal with several key links, otherwise it will easily lead to data loss or structural chaos.

Preparation: Find out your data and structure

Before you start, you must first figure out what your original data looks like. For example, the original database type (such as Oracle, PostgreSQL or SQL Server), table structure, field type, index, and primary key settings must be sorted out clearly. MySQL and other systems support differently on some data types, such as the ENUM type may not be available in other systems, or the behavior of TIMESTAMP is also somewhat different.

You can do this:

• Export the DDL (data definition language) statement of the original database and see the table structure
• Check if there are stored procedures, triggers, or views that need to be migrated
• Confirm whether the character set is consistent, such as whether UTF-8 is compatible with MySQL's utf8mb4

The most easily overlooked step is the encoding problem, especially in the Chinese environment. If the source library uses GBK, and you don’t pay attention to the conversion when moving to MySQL, you will find a lot of garbled code later.

Data export and format conversion: choosing the right tool is very important

The most common method of exporting data is to use the export functions of the original database, such as PostgreSQL's pg_dump, Oracle's expdp, and some scripts to convert. You can also use ETL tools such as Talend, Pentaho, or even write Python scripts to parse raw data files.

Common practices include:

• Use CSV files as intermediate format
• Use the export command provided by the database to add --data-only or similar parameters to only export data
• Pay attention to dealing with special characters, such as line breaks, quotation mark nesting and other issues

For example, if you export data from Excel and a field in it has double quotes and is not escaped, an error may be reported when importing MySQL. Therefore, it is best to add escape rules when exporting, or pre-process them with a text editor before importing.

Data import into MySQL: Don't rush to import it in one breath

The most common way to import MySQL is LOAD DATA INFILE or mysqlimport . Of course, you can also use client tools such as Navicat and DBeaver. However, it is recommended to test in small batches first at the beginning, and then batch operations after confirming that there is no problem.

Here are a few practical suggestions:

• Create the target table structure first, and do not rely on automatic table creation
• If the data volume is large, consider closing the index or foreign key constraints and rebuild after the import is completed.
• Logging is very important, it is convenient to track which batch of problems are wrong.

Sometimes you will find that a certain table is imported very slowly, which may be caused by frequent index conflicts. At this time, you can first remove the constraints and then verify and repair them uniformly after the import is completed.

Verification and subsequent adjustments: Don't forget the last step

After the import is completed, everything will not be fine, and the data consistency must be verified. You can judge whether there are any omissions or misalignments by comparing the total number of records and randomly checking several data contents. If there is a self-increasing ID, you must also confirm whether it is continuous or whether it has affected the business logic.

Also note:

• Update statistics (ANALYZE TABLE)
• Re-establishing the relationship between index and foreign keys
• Modify user permissions to ensure the security of new database access

The most common problem at this stage is the time type fields. For example, some databases store dates with milliseconds by default, while MySQL is only retained for seconds. If you are not careful, it will cause accuracy loss.

Basically these steps. Migration seems simple, but each link has some details to pay attention to, especially migration between systems with large structural differences, and it should not be taken lightly.

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