MySQL从表左选择与CSV导出联接

Question

I have tables that are on different mysql instances. I want to export some data as csv from a mysql instance, and perform a left join on a table with the exported csv data. How can I achieve this?

Answer 1

Quite surprisingly that is possible with MySQL, there are several steps that you need to go through.

1. First create a template table using CSV engine and desired table layout. This is the table into which you will import your CSV file. Use CREATE TABLE yourcsvtable (field1 INT NOT NULL, field2 INT NOT NULL) ENGINE=CSV for example. Please note that NULL values are not supported by CSV engine.
2. Perform you SELECT to extract the CSV file. Eg SELECT * FROM anothertable INTO OUTFILE 'temp.csv' FIELDS TERMINATED BY ',';
3. Copy temp.csv into your target MySQL data directory as yourcsvtable.CSV . Location and exact name of this file depends on your MySQL setup. You cannot perform the SELECT in step 2 directly into this file as it is already open - you need to handle this in your script.
4. Use FLUSH TABLE yourcsvtable; to reload/import the CSV table.

Now you can execute your query against the CSV file as expected.

Depending on your data you need to ensure that the data is correctly enclosed by quotation marks or escaped - this needs to be taken into account in step 2.

CSV file can be created by MySQL on some another server or by some other application as long as it is well-formed.

Answer 2

If you export it as CSV, it's no longer SQL, it's just plain row data. Suggest you export as SQL, and import into the second database.