3.6.1. Inserts

INSERT INTO table_name (column1, column2, ..., columnN)
VALUES (value1, value2, ..., valueN)

Under this syntax, you specify the columns followed by the values to populate those columns for the new row. When inserting data into numeric fields, you can insert the value as is; for all other fields, you must wrap them in single quotes. For example, to insert a row of data into a table of addresses, you might issue the following command:

INSERT INTO addresses (name, address, city, state, phone, age)
VALUES('Irving Forbush', '123 Mockingbird Lane', 'Corbin', 'KY',
       '(800) 555-1234', 26)

# Insert info for the directory Stacie's Directory which
# is in c:\Personal\Stacie
INSERT INTO files (description, location) 
VALUES ('Stacie\'s Directory', 'C:\\Personal\\Stacie')

MySQL allows you to leave out the column names as long as you specify a value for every column in the table in the order they were specified in the table's CREATE call. If you want to use the default values for a column, however, you must specify the names of the columns for which you intend to insert nondefault data. For example, if the earlier files table had contained a column called size, the default value would be used for Stacie's Directory. MySQL allows you to specify a custom default value in the table's CREATE call. If you do not have a default value set up for a column, and that column is NOT NULL, you must include that column in the INSERT statement with a non-NULL value.

Newer versions of MySQL support a nonstandard INSERT call for inserting multiple rows at once:

INSERT INTO foods VALUES (NULL, 'Oranges', 133, 0, 2, 39),
                         (NULL, 'Bananas', 122, 0, 4, 29),
                         (NULL, 'Liver', 232, 3, 15, 10)

Another nonstandard syntax supported by MySQL enables you to specify the column name and value together:

INSERT INTO book SET title='The Vampire Lestat', author='Anne Rice';

Finally, you can insert data by using the data from some other table (or group of tables) to populate your new table. For example:

INSERT INTO foods (name, fat)
SELECT food_name, fat_grams FROM recipes

You should note that the number of columns in the INSERT call matches the number of columns in the SELECT call. In addition, the data types for the INSERT columns must match the data types for the corresponding SELECT columns. Finally, the SELECT clause in an INSERT statement cannot contain an ORDER BY modifier and cannot be selected from the same table where the INSERT occurs.

3.6.2. Sequence Generation

To achieve this, simply make a numeric primary key that increments every time you insert a new row. Looking at the cities table shown earlier, the first city you insert would have an id of 1, the second 2, the third 3, and so on. To successfully manage this primary key sequencing, you need some way to guarantee that a number can be read and incremented by only one client at a time. You accomplish this task by making the primary key field AUTO_INCREMENT.

CREATE TABLE cities (id      INT  NOT NULL PRIMARY KEY AUTO_INCREMENT,
                     name    VARCHAR(100),
                     pop     INT,
                     founded DATE)

The first time you insert a row, the id field for your first row will be 1 as long as you use NULL or 0 for that field in the INSERT statement. For example, this command takes advantage of the AUTO_INCREMENT feature:

INSERT INTO cities (id, name, pop)
VALUES (NULL, 'Houston', 3000000)

If no other values are in that table when you issue this command, MySQL will set this field to 1, not NULL (remember, it cannot be NULL). If other values are present in the table, the value inserted will be one greater than the largest current value for id.

UPDATE table_name SET id=LAST_INSERT_ID( id+1 );

The AUTO_INCREMENT attribute may be supplied for at most one column of an integer type in a table. In addition to being an integer type, the column must be either a primary key or the sole column in a unique index. When you attempt an insert into a table with such an integer field and fail to specify a value for that field (or specify a NULL value), a value of one greater than the column's current maximum value will be automatically inserted.

3.6.3. Updates

UPDATE table_name
SET column1=value1, column2=value2, ..., columnN=valueN
[WHERE clause]

In addition to assigning literal values to a column, you can also calculate the values. You can even calculate the value based on a value in another column:

UPDATE years
SET end_year = begin_year+5

This command sets the value in the end_year column equal to the value in the begin_year column plus 5 for each row in that table.

3.6.4. The WHERE Clause

UPDATE bands
SET lead_singer = 'Ian Anderson'
WHERE band_name = 'Jethro Tull'

This UPDATE specifies that you should change only the lead_singer column for the row where band_name is identical to Jethro Tull. If the band_name column is not a unique index, that WHERE clause may match multiple rows. Many SQL commands employ WHERE clauses to help pick out the rows on which you wish to operate. Because the columns in the WHERE clause are columns on which you search, you should generally have indexes created around whatever combinations you commonly use. We discuss the kinds of comparisons you can perform in the WHERE clause later in the chapter.

3.6.5. Deletes

DELETE FROM table_name [WHERE clause]

As with other commands that accept a WHERE clause, the WHERE clause is optional. If you omit it, you will delete all of the records in the table! Of all the destructive commands in SQL, this is the easiest one to issue by mistake.

MySQL 4.0 has introduced a new, dangerous form of DELETE that supports the ability to delete from multiple tables with a single command:

DELETE table1, table2, ..., tablen
FROM table1, table2, ... tablen
[WHERE clause]

DELETE Author, Address
FROM Author, Book, Address
WHERE Author.author_id = Addess.address_id
AND Author.author_id = Book.author_id
AND Book.publish_date < 1980;