MySQL Crash Course #10# Chapter 19. Inserting Data

INDEX

• BAD EXAMPLE
• Improving Overall Performance
• Inserting Multiple Rows INSTEAD OF Inserting a Single Row
• Inserting Retrieved Data

BAD EXAMPLE

INSERT INTO Customers
VALUES(NULL,
   'Pep E. LaPew',
   '100 Main Street',
   'Los Angeles',
   'CA',
   '',
   'USA',
   NULL,
   NULL);

Always Use a Columns List As a rule, never use INSERT without explicitly specifying the column list. This will greatly increase the probability that your SQL will continue to function in the event that table changes occur.

Improving Overall Performance

Databases are frequently accessed by multiple clients, and it is MySQL's job to manage which requests are processed and in which order. INSERT operations can be time consuming (especially if there are many indexes to be updated), and this can hurt the performance of SELECT statements that are waiting to be processed.

If data retrieval is of utmost importance (as is usually is), you can instruct MySQL to lower the priority of your INSERT statement by adding the keyword LOW_PRIORITY in between INSERT and INTO, like this:

INSERT LOW_PRIORITY INTO

Incidentally, this also applies to the UPDATE and DELETE statements that you'll learn about in the next chapter.

Inserting Multiple Rows INSTEAD OF Inserting a Single Row

INSERT INTO customers(cust_name,
   cust_address,
   cust_city,
   cust_state,
   cust_zip,
   cust_country)
VALUES(
        'Pep E. LaPew',
        '100 Main Street',
        'Los Angeles',
        'CA',
        '',
        'USA'
     ),
      (
        'M. Martian',
        '42 Galaxy Way',
        'New York',
        'NY',
        '',
        'USA'
   );

Improving INSERT Performance This technique can improve the performance of your database possessing, as MySQL will process multiple insertions in a single INSERT faster than it will multiple INSERT statements.

Inserting Retrieved Data

INSERT INTO customers(cust_id,
    cust_contact,
    cust_email,
    cust_name,
    cust_address,
    cust_city,
    cust_state,
    cust_zip,
    cust_country)
SELECT cust_id,
    cust_contact,
    cust_email,
    cust_name,
    cust_address,
    cust_city,
    cust_state,
    cust_zip,
    cust_country
FROM custnew;

PS. 列名可以不对应，列的值类型对应就可以了。