1 introduction to my sql

 To log in to mysql monitor:
 Mysql –u root
 MySQL monitor

 To log out, just type exit or quit

 Selecting a Database
 Mysql> show databases;
 Selecting a Database
 Mysql> use guitars;
 If you forget which database is selected use
the select database(); statement

 Mysql> create database guitars;
 Mysql> use guitars;
 Mysql> select database();

 Mysql> drop database guitars;

 The table creation command requires
 Name of the table
 Names of fields
 Definitions for each field
 The generic table creation syntax is:
 CREATE TABLE table_name (column_name
column_type);

 The table name is up to you of course, but
should be a name that reflects the usage of the
table.
 For example, if you have a table that holds the
inventory of a grocery store, you wouldn't name
the table s. You would probably name it
something like grocery_inventory.
 Similarly, the field names you select should be as
concise as possible and relevant to the function
they serve and the data they hold. For example,
you might call a field holding the name of an
item item_name, not n.

mysql> CREATE TABLE grocery_inventory (
-> id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
-> item_name VARCHAR (50) NOT NULL,
-> item_desc TEXT,
-> item_price FLOAT NOT NULL,
-> curr_qty INT NOT NULL -> );
Query OK, 0 rows affected (0.02 sec)
 The MySQL server responds with Query OK
each time a command, regardless of type, is
successful.

 INSERT INTO table_name (column list) VALUES
(column values);
 Within the parenthetical list of values, you must enclose
strings within quotation marks.
 The SQL standard is single quotes, but MySQL enables
the usage of either single or double quotes. Remember
to escape the type of quotation mark used, if it's within
the string itself.
 Integers do not require quotation marks around them.

 Two main parts of the INSERT statement:
 Column list
 Value List
 Only the value list is actually required, but if
you omit the column list, you must
specifically provide for each column in your
value list in the exact order.

 A statement with all columns named:

 INSERT INTO grocery_inventory (id, item_name, item_desc,
item_price, curr_qty) VALUES ('1', 'Apples', 'Beautiful, ripe
apples.', '0.25', 1000);
 A statement that uses all columns but does
not explicitly name them:

 INSERT INTO grocery_inventory VALUES ('2', 'Bunches of
Grapes', 'Seedless grapes.', '2.99', 500);

mysql> INSERT INTO grocery_inventory
-> (id, item_name, item_desc, item_price, curr_qty)
-> VALUES
-> (1, 'Apples', 'Beautiful, ripe apples.', 0.25, 1000);
 Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO grocery_inventory VALUES (2, 'Bunches
of Grapes',
-> 'Seedless grapes.', 2.99, 500);
 Query OK, 1 row affected (0.01 sec)

 Now for some more interesting methods of using INSERT.
Because id is an auto-incrementing integer, you don't have
to put it in your value list.
 However, if there's a value you specifically don't want to list
(such as id), you then must list the remaining columns in use.
For example, the following statement does not list the
columns and also does not give a value for id, and it produces
an error:

 mysql> INSERT INTO grocery_inventory VALUES ->
('Bottled Water (6-pack)', '500ml spring water.', 2.29, 250);
ERROR 1136: Column count doesn't match value count at
row 1

 Because you didn't list any columns, MySQL
expects all of them to be in the value list,
causing an error on the previous statement.
 If the goal was to let MySQL do the work for
you by auto-incrementing the id field, you
could use either of these statements:

 INSERT INTO grocery_inventory
(item_name, item_desc, item_price,
curr_qty) VALUES ('Bottled Water (6-pack)',
'500ml spring water.', '2.29', 250);

 A statement that uses all columns, but does
not explicitly name them and indicates a
NULL enTRy for id (so one is filled in for you):

 INSERT INTO grocery_inventory VALUES
('NULL', 'Bottled Water (12-pack)', '500ml
spring water.', 4.49, 500);

 SELECT is the SQL command used to retrieve
records from your tables.
 This command syntax can be totally
simplistic or very complicated, depending on
which fields you want to select, whether you
want to select from multiple tables, and what
conditions you plan to impose.

 SELECT expressions_and_columns
 FROM table_name
 [WHERE some_condition_is_true]
 [ORDER BY some_column [ASC | DESC]]
[LIMIT offset, rows]

 * stands for everything.
 So, to select everything (all rows, all
columns) from the grocery_inventory table,
your SQL statement would be:
 SELECT * FROM grocery_inventory;

 If you only want to select specific columns,
replace the * with the names of the columns,
separated by commas.

 Results of SELECT queries are ordered as
they were inserted into the table and
shouldn't be relied on as a meaningful
ordering system.
 If you want to order results a specific way,
such as by date, ID, name, and so on, specify
your requirements using the ORDER BY
clause.

 When selecting results from a table without
specifying a sort order, the results may or may
not be ordered by their key value.
 This occurs because MySQL reuses the space
taken up by previously deleted rows.
 In other words, if you add records with ID values
of 1 through 5, delete the record with ID number
4, and then add another record (ID number 6),
the records might appear in the table in this
order: 1, 2, 3, 6, 5.

 The default sorting of ORDER BY is
ascending (ASC); strings sort from A to Z,
integers start at 0, dates sort from oldest to
newest. You can also specify a descending
sort, using DESC:

 You can use the LIMIT clause to return only a
certain number of records from your SELECT
query result.
 There are two requirements when using the
LIMIT clause:
 the offset and the number of rows. The offset is
the starting position,
 and the number of rows should be self-
explanatory.

 Suppose you had more than two or three
records in the grocery_inventory table, and
you wanted to select the ID, name, and
quantity of the first two, ordered by curr_qty.
 In other words, you want to select the two
items with the least inventory. The following
single-parameter limit will start at the 0
(zero) position and go to the second record:

 You have learned numerous ways to retrieve
particular columns from your tables but not
specific rows.
 This is when the WHERE clause comes in to
play. From the example SELECT syntax, you
see that WHERE is used to specify a particular
condition:
 SELECT expressions_and_columns FROM
table_name

Operator Meaning
= Equal To
!= Not equal to
<= Less than or Equal to
< Less Than
>= Greater than or equal to
> Greater than

 There's also a handy operator called BETWEEN, which is
useful with integer or data comparisons because it searches
for results between a minimum and maximum value. For
example:

 Other operators include logical operators, which
enable you to use multiple comparisons within
your WHERE clause.
 The basic logical operators are AND and OR.
 When using AND, all comparisons in the clause
must be true to retrieve results, whereas
 Using OR allows a minimum of one comparison
to be true.
 Also, you can use the IN operator to specify a
list of items that you want to match.

 You were introduced to matching strings
within a WHERE clause by using = or !=, but
there's another useful operator for the
WHERE clause when comparing strings:
 The LIKE operator. This operator uses two
characters as wildcards in pattern matching:
 % Matches multiple characters
 Matches exactly one character

 For example, if you want to find records in
the grocery_inventory table where the first
name of the item starts with the letter A, you
would use

 You're not limited to selecting only one table
at a time. That would certainly make
application programming a long and tedious
task! When you select from more than one
table in one SELECT statement, you are
really joining the tables together.
 Suppose you have two tables: fruit and color.
You can select all rows from each of the two
tables by using two separate SELECT
statements:

 When you want to select from both tables at
once, there are a few differences in the
syntax of the SELECT statement.
 First, you must ensure that all the tables
you're using in your query appear in the
FROM clause of the SELECT statement.
 Using the fruit and color example, if you
simply want to select all columns and rows
from both tables, you might think you would
use the following SELECT statement:

 When you select from multiple tables, you must build
proper WHERE clauses to ensure that you really get
what you want.
 In the case of the fruit and color tables, what you
really want is to see the fruitname and colorname
records from these two tables where the IDs of each
match up.
 This brings us to the next nuance of the query how to
indicate exactly which field you want when the fields
are named the same in both tables!
 Simply, you append the table name to the field name,
like this:
 tablename.fieldname

 UPDATE is the SQL command used to
modify the contents of one or more columns
in an existing record or set of records. The
most basic UPDATE syntax looks like this:

 UPDATE table_name SET column1='new
value', column2='new value2‘

 You must be careful and use a condition when
updating a table, unless you really intend to
change all the columns for all records to the
same value.
 For the sake of argument, assume that "grape"
is spelled incorrectly in the table, and you want
to use UPDATE to correct this mistake. This
query would have horrible results:
 mysql> UPDATE fruit SET fruit_name = 'grape';
Query OK, 4 rows affected (0.00 sec) Rows
matched: 4 Changed: 4 Warnings: 0

 Assume your fruit table has not been
completely filled with grapes but instead
contains four records, one with a spelling
mistake (grappe instead of grape).
 The UPDATE statement to fix the spelling
mistake would be
 mysql> UPDATE fruit SET fruit_name =
'grape' WHERE fruit_name = 'grappe';

 When someone purchases a product, the
inventory table should be updated
accordingly. However, you won't know
exactly what number to enter in the curr_qty
column, just that you sold one. In this case,
use the current value of the column and
subtract 1:
 mysql> UPDATE grocery_inventory SET
curr_qty = curr_qty - 1 WHERE id = 1;

 Another method for modifying records is to use
the REPLACE command, which is remarkably
similar to the INSERT command.
 REPLACE INTO table_name (column list)
VALUES (column values);
 The REPLACE statement works like this: If the
record you are inserting into the table contains a
primary key value that matches a record already
in the table, the record in the table will be
deleted and the new record inserted in its place.

 Using the grocery_inventory table, the
following command replaces the entry for
Apples:
 mysql> REPLACE INTO grocery_inventory
VALUES -> (1, 'Granny Smith Apples',
'Sweet!', '0.50', 1000);
 Query OK, 2 rows affected (0.00 sec)

 The basic DELETE syntax is
 DELETE FROM table_name
 [WHERE some_condition_is_true] [LIMIT rows]
 Notice there is no column specification used in
the DELETE commandwhen you use DELETE,
the entire record is removed.
 You might recall the fiasco earlier in this chapter,
regarding grapes in the fruit table, when
updating a table without specifying a condition
caused all records to be updated.
 You must be similarly careful when using
DELETE.

 Assuming the following structure and data in
a table called fruit:
 mysql> SELECT * FROM fruit;

 mysql> DELETE FROM fruit;
You can always verify the deletion by
attempting to SELECT data from the table. If
you issued this command after removing all
the records:
 mysql> SELECT * FROM fruit;
 Empty set (0.00 sec)

 A conditional DELETE statement, just like a
conditional SELECT or UPDATE statement, means
you are using WHERE clauses to match specific
records.
 You have the full range of comparison and logical
operators available to you, so you can pick and choose
which records you want to delete.
 A prime example would be to remove all records for
rotten fruit from the fruit table:
 mysql> DELETE FROM fruit WHERE status =
'rotten';

 DELETE FROM table_name
 [ORDER BY some_column [ASC | DESC]]
[LIMIT rows]

 To remove the oldest record, first use ORDER
BY to sort the results appropriately, and then
use LIMIT to remove just one record:

1 introduction to my sql

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1 introduction to my sql