MySQL/Syntax: Unterschied zwischen den Versionen

Version vom 16. September 2011, 13:33 Uhr

Inhaltsverzeichnis

1 Connect to mysql
2 CREATE/COPY tables
3 SELECT's
- 3.1 SELECT DB- and/or Table-Sizes
4 UPDATE / ALTER
5 SHOW
6 Users, Passwords and Rights
7 Backup/Dump/Copy
8 Optimizer stuff
9 Misc

Connect to mysql

To login (from unix shell) use -h only if needed.

# mysql -h hostname -u root -p

Create a database on the sql server.

mysql> create database [databasename];

List all databases on the sql server.

mysql> show databases;

Switch to a database.

mysql> use [db name];

To see all the tables in the db.

mysql> show tables;

To see database's field formats.

mysql> DESCRIBE [table name];
mysql> SHOW CREATE table [table name] \G

To delete a db.

mysql> drop database [database name];

To delete a table.

mysql> drop table [table name];

Show all data in a table.

mysql> SELECT * FROM [table name];

Returns the columns and column information pertaining to the designated table.

mysql> show columns from [table name];

CREATE/COPY tables

Create Table Example 1.

mysql> CREATE TABLE [table name] (firstname VARCHAR(20), middleinitial VARCHAR(3), lastname VARCHAR(35),suffix VARCHAR(3),officeid
VARCHAR(10),userid VARCHAR(15),username VARCHAR(8),email VARCHAR(35),phone VARCHAR(25), groups VARCHAR(15),datestamp DATE,timestamp time,pgpemail
VARCHAR(255));

Create Table Example 2.

mysql> create table [table name] (personid int(50) not null auto_increment primary key,firstname varchar(35),middlename
varchar(50),lastnamevarchar(50) default 'bato');

Copy a table

CREATE TABLE student2 SELECT * FROM student;

SELECT's

select into OUTFILE e.g. .csv

SELECT dl . * , ht.typ, h.hersteller
INTO OUTFILE "/tmp/goober_downloads.txt"
FIELDS TERMINATED BY ','
FROM `downloads` dl
JOIN handy_typen ht ON dl.handyid = ht.handyid
JOIN handy_hersteller h ON dl.herstellerid = h.herstellerid
WHERE dldate > '2006-05-14'

select into table

mysql>  INSERT INTO tbl_temp2 (fld_id)
          SELECT tbl_temp1.fld_order_id
          FROM tbl_temp1 WHERE tbl_temp1.fld_order_id > 100;

Show certain selected rows with the value "whatever".

mysql> SELECT * FROM [table name] WHERE [field name] = "whatever";

Show all records containing the name "Bob" AND the phone number '3444444'.

mysql> SELECT * FROM [table name] WHERE name = "Bob" AND phone_number = '3444444';

Show all records not containing the name "Bob" AND the phone number '3444444' order by the phone_number field.

mysql> SELECT * FROM [table name] WHERE name != "Bob" AND phone_number = '3444444' order by phone_number;

Show all records starting with the letters 'bob' AND the phone number '3444444'.

mysql> SELECT * FROM [table name] WHERE name like "Bob%" AND phone_number = '3444444';

Show all records starting with the letters 'bob' AND the phone number '3444444' limit to records 1 through 5.

mysql> SELECT * FROM [table name] WHERE name like "Bob%" AND phone_number = '3444444' limit 1,5;

Use a regular expression to find records. Use "REGEXP BINARY" to force case-sensitivity. This finds any record beginning with a.

mysql> SELECT * FROM [table name] WHERE rec RLIKE "^a";

Show unique records.

mysql> SELECT DISTINCT [column name] FROM [table name];

Show selected records sorted in an ascending (asc) or descending (desc).

mysql> SELECT [col1],[col2] FROM [table name] ORDER BY [col2] DESC;

Return number of rows.

mysql> SELECT COUNT(*) FROM [table name];

Sum column.

mysql> SELECT SUM(*) FROM [table name];

Join tables on common columns.

mysql> select lookup.illustrationid, lookup.personid,person.birthday from lookup left join person on
lookup.personid=person.personid=statement to join birthday in person table with primary illustration id;

SELECT DB- and/or Table-Sizes

get size of all db-tables:

SELECT TABLE_SCHEMA AS 'Database', TABLE_NAME AS 'Table',
CONCAT(ROUND(((DATA_LENGTH + INDEX_LENGTH - DATA_FREE) / 1024 / 1024),2)," Mb") AS Size FROM INFORMATION_SCHEMA.TABLES;

get size of specific DB-table:

SELECT TABLE_SCHEMA AS 'Database', TABLE_NAME AS 'Table',
CONCAT(ROUND(((DATA_LENGTH + INDEX_LENGTH - DATA_FREE) / 1024 / 1024),2)," MB") AS Size FROM INFORMATION_SCHEMA.TABLES 
where TABLE_SCHEMA like '%YOUR_DB_NAME%';

get size of entire DB:

SELECT CONCAT(sum(ROUND(((DATA_LENGTH + INDEX_LENGTH - DATA_FREE) / 1024 / 1024),2))," MB") AS Size 
FROM INFORMATION_SCHEMA.TABLES where TABLE_SCHEMA like '%YOUR_DB_NAME%' ;

UPDATE / ALTER

To update info already in a table.

mysql> UPDATE [table name] SET Select_priv = 'Y',Insert_priv = 'Y',Update_priv = 'Y' where [field name] = 'user';

Delete a row(s) from a table.

mysql> DELETE from [table name] where [field name] = 'whatever';

Delete a column.

mysql> alter table [table name] drop column [column name];

Add a new column to db.

mysql> alter table [table name] add column [new column name] varchar (20);

Change column name.

mysql> alter table [table name] change [old column name] [new column name] varchar (50);

Make a unique column so you get no dupes.

mysql> alter table [table name] add unique ([column name]);

Make a column bigger.

mysql> alter table [table name] modify [column name] VARCHAR(3);

Add new column AND index over that column:

mysql> alter table [table name] add [NEW column name] INT(11) not null default 0 after [existent column name], 
       add index [NEW column name]_idx ([NEW column name]);

Add primary key to column

ALTER TABLE [table name] ADD PRIMARY KEY ([column name]);

Delete unique from table.

mysql> alter table [table name] drop index [colmn name];

Load a CSV file into a table.

mysql> LOAD DATA INFILE '/tmp/filename.csv' replace INTO TABLE [table name] FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' (field1,field2,field3);

SHOW

some SHOW statements

show create table statement

SHOW CREATE TABLE [table] \G

show variables set by *.cnf or daemon-parameter

SHOW VARIABLES;

or

SHOW VARIABLES LIKE 'query_cache_%';

Users, Passwords and Rights

Creating a new user. Login as root. Switch to the MySQL db. Make the user. Update privs.

# mysql -u root -p
mysql> use mysql;
mysql> INSERT INTO user (Host,User,Password) VALUES('%','username',PASSWORD('password'));
mysql> flush privileges;

Change a users password from unix shell.
Better use 'GRANT'-syntax

# mysqladmin -u username -h hostname.blah.org -p password 'new-password'

Change a users password from MySQL prompt. Login as root. Set the password. Update privs.

# mysql -u root -p
mysql> SET PASSWORD FOR 'user'@'hostname' = PASSWORD('passwordhere');
mysql> flush privileges;

Set a root password if there is no root password.

# mysqladmin -u root password [new_super_secure_password]

Update a root password.

# mysqladmin -u root -p oldpassword newpassword

Allow the user "bob" to connect to the server from localhost using the password "passwd". Login as root. Switch to the MySQL db. Give privs. Update privs.

# mysql -u root -p
mysql> use mysql;
mysql> grant usage on *.* to bob@localhost identified by 'passwd';
mysql> flush privileges;

Give user privilages for a db. Login as root. Switch to the MySQL db. Grant privs. Update privs.

# mysql -u root -p
mysql> use mysql;
mysql> INSERT INTO user (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,Create_priv,Drop_priv) VALUES
('%','databasename','username','Y','Y','Y','Y','Y','N');
mysql> flush privileges;

or

mysql> grant all privileges on databasename.* to username@localhost identified by 'passwd' [WITH GRANT OPTION];
mysql> flush privileges;

set password for user

SET PASSWORD FOR openser@'%'=PASSWORD('123456');
SET PASSWORD FOR openser@localhost=PASSWORD('123456');

setze rechte

GRANT ALL PRIVILEGES ON asterisk.* TO asteriskuser@localhost IDENTIFIED BY 'amp109';

setze rechte inkl. grant-recht
heisst der user darf rechte vergeben...

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' WITH GRANT OPTION;

Backup/Dump/Copy

Backup/Dump or copy data

structure AND data

Dump all databases for backup. Backup file is sql commands to recreate all db's.

# mysqldump -u root -ppassword --opt >/tmp/alldatabases.sql

Dump one database for backup.

# mysqldump -u username -ppassword --databases databasename >/tmp/databasename.sql

Dump a table from a database.

# mysqldump -c -u username -ppassword databasename tablename > /tmp/databasename.tablename.sql

Restore database (or database table) from backup.

# mysql -u username -ppassword databasename < /tmp/databasename.sql

structure only

# mysqldump -u username -ppassword --no-data --databases databasename >/tmp/databasename.structure.sql

COPY databases

Copy database on the same host

mysql> create database [DBname of COPY]
mysql> mysqldump [orig. DBname] | mysql [DBname of COPY]

use -h option to mysqldump or mysql to pull/push db from/to a remote host

hotcopy

see: LVM

Optimizer stuff

mysql> explain extended select ...;
mysql> show warnings \G

Shows what the optimizer actually did. In this example, An IN was converted to EXISTS

Misc

Random SELECT

My solution to this problem is using User Defined Variables. Let’s say we want X random rows from a table myTable.

SELECT myTable.* FROM (SELECT FLOOR (RAND() * (SELECTcount(*) FROM myTable)) num ,@num:=@num+1 from (SELECT @num:=0) a , myTable LIMIT X) b , 
myTable WHERE b.num=myTable.id;

I will try to explain some of the parts:

FLOOR (RAND() * (SELECT count(*) FROM myTable)) num - produce an integer value between 0 to the max rows this table has
(SELECT @num:=0) a – initialize the User Defined Variable a to zero
(SELECT FLOOR (RAND() * (SELECTcount(*) FROM myTable)) num ,@num:=@num+1 from (SELECT @num:=0) a , myTable LIMIT X) b – produces X random integer numbers

If you need it with range, say X random rows from a table myTable with a range from S to T you can write it like this:

SELECT myTable.* FROM (SELECT FLOOR (S + RAND() * (T – S)) num ,@num:=@num+1 FROM (SELECT @num:=0) a , myTable LIMIT X) b ,  myTable 
WHERE b.num=myTable.id;

Some caution:
because this query uses User Defined Variable (@num) which are connection specific, you can NOT use this MySQL query with a system that uses connection pooling or persistent connections.

If there are some holes in the table you can fix it by:

SELECT (SELECT myTable2.id from myTable myTable2 where myTable2.id>=b.num LIMIT 1) c 
FROM (SELECT FLOOR(RAND() * (SELECTcount(*) 
FROM myTable)) num ,@num:=@num+1 
FROM (SELECT @num:=0) a , myTable LIMIT X) b ;

To improve performance you can combine this solution with a left join:

SELECT IF(c.id is null, (SELECT c2.id FROM myTable c2 WHERE c2.id > b.num LIMIT 1), c.id) d 
FROM (SELECT FLOOR(RAND() * (SELECTcount(*) FROM myTable)) num ,@num:=@num+1 
FROM (SELECT @num:=0) a , myTable LIMIT X) b LEFT JOIN myTable c ON( c.id=b.num);

fragmented tables

SELECT COUNT(TABLE_NAME) 
FROM information_schema.TABLES 
WHERE TABLE_SCHEMA NOT IN ('information_schema','mysql') 
AND Data_free > 0 AND NOT ENGINE='MEMORY';

anzahl fragmentierter tabellen auslesen

SELECT concat(TABLE_SCHEMA, ".", TABLE_NAME)
FROM information_schema.TABLES 
WHERE TABLE_SCHEMA NOT IN ('information_schema','mysql') 
AND Data_free > 0 AND NOT ENGINE='MEMORY';

namen fragmentierter tabellen auslesen

OPTIMIZE TABLE db.table1, db.table2, db2.table1, ...;

defragmentieren ;-)

Crashed Tables

CHECK TABLE [tabelle]

and

REPAIR TABLE [tabelle]

if that does not do the job try:

mysqladmin shutdown          # (or use init-script)
myisamchk *.MYI

or

myisamchk -e *.MYI           # if you have more time.

perhaps use -s (silent) option

after that first run:

myisamchk -r -q [tabelle]

to try an quick recover

if that didn't do the job:

create a backup of you database-files (*.frm, *.MYD, *.MYI)
```
myisamchk -r
```
to recover
if previous step failed:
```
myisamchk --safe-recover [tabelle]
```
if that all does not work refer to: Mysql-Page