mysql distinct ¶Ô¶à×ֶιýÂ˲»ÕýÈ·µÄ½â¾ö·½·¨
ÏÂÃæÏÈÀ´¿´¿´Àý×Ó£º
table
id name
1 a
2 b
3 c
4 c
5 b
¿â½á¹¹´ó¸ÅÕâÑù£¬ÕâÖ»ÊÇÒ»¸ö¼òµ¥µÄÀý×Ó£¬Êµ¼ÊÇé¿ö»á¸´Ôӵöࡣ
±ÈÈçÎÒÏëÓÃÒ»ÌõÓï¾ä²éѯµÃµ½name²»Öظ´µÄËùÓÐÊý¾Ý£¬ÄǾͱØÐëʹÓÃdistinctÈ¥µô¶àÓàµÄÖØ¸´¼Ç¼¡£
select distinct name from table
µÃµ½µÄ½á¹ûÊÇ:
name
a
b
c
ºÃÏñ´ïµ½Ð§¹ûÁË£¬¿ÉÊÇ£¬ÎÒÏëÒªµÃµ½µÄÊÇidֵĨ£¿¸ÄһϲéѯÓï¾ä°É:
select distinct name, id from table
½á¹û»áÊÇ:
id name
1 a
2 b
3 c
4 c
5 b
distinctÔõôûÆð×÷Óã¿×÷ÓÃÊÇÆðÁ˵쬲»¹ýËûͬʱ×÷ÓÃÁËÁ½¸ö×ֶΣ¬Ò²¾ÍÊDZØÐëµÃidÓëname¶¼ÏàͬµÄ²Å»á±»Åųý¡£¡£¡£¡£¡£¡£¡£
½â¾ö·½·¨: select id, name from table group by name
¹þ¹þ£¡ÇëÊÊÓ¦MYSQLµÄд·¨°É
Ïà¹ØÎĵµ£º
MySQL showµÄÓ÷¨
a. show tables»òshow tables from database_name; // ÏÔʾµ±Ç°Êý¾Ý¿âÖÐËùÓбíµÄÃû³Æ
b. show databases; // ÏÔʾmysqlÖÐËùÓÐÊý¾Ý¿âµÄÃû³Æ
c. show columns from table_name from database_name; »òshow columns from database_name.table_name; ......
ÎÒÓõÄÊÇmysql5.0£¬
ÎÒ³ÌÐòÖÐÓõ½ÁËÒ»¾äsqlÊÇ
SQL code
select count(DISTINCT id) from Policyinfo p where p.filename not in
(select p2.filename from Policyreadinfo p2 where p2.reader='test')
µ«ÊÇÿ´ÎÔÚ³ÌÐòÖÐÿ´ÎÖ´ÐÐÕâ¾äsqlÊ±ÍøÒ³¾ÍÌØÂý£¬Òª10¶àÃ룬¶øÕâ2¸ö±íµÄ¼Ç¼ÐÐÊýÒ²¾Í1000¶à¶øÒÑ£¬ÎÒ°ÑÕâ¾äsqlµ¥¶ÀÄ ......
Èç¹ûÒªÁ˽âMySQLÊý¾Ý¿âËø¶¨»úÖÆ£¬Ê×ÏÈÁ˽âÒ»ÏÂMySQLµÄÈýÖÖËø¶¨ÀàÐÍ£º
Ò»£¬Ðм¶Ëø¶¨
¶þ£¬±í¼¶Ëø¶¨
Èý£¬Ò³¼¶Ëø¶¨
ÕâÈýÖÖËø¶¨ÀàÐÍ£¬ÔÚMySQLÊý¾Ý¿âÖÐʹÓÃÈçÏ£º
Ðм¶Ëø¶¨£ºMyISAM£¬Memory£¬CSV[·ÇÊÂÎñÐԵĴ洢ÒýÇæ]
±í¼¶Ëø¶¨£ºInnoDB£¬NDB Chuster
Ò³¼¶Ëø¶¨£ºBerkeley DB
Á½ÖÖËø¶¨»úÖÆ£º¶ÁËø¶¨ºÍÐ´Ëø¶¨
MySQLÊý¾Ý¿âËø¶ ......
windows주
½â¾ö°ì·¨£º
1.¼ì²éÄãµÄMysqlĿ¼ÓÐûÓиøÏµÍ³µÄSystemÓû§È¨ÏÞ¡£
2.ɾ³ýµôÄãµÄ %WINDOWS%/my.ini Îļþ¡£
3.¼ì²éÄãµÄ c:/my.cnf ÎļþÅäÖÃÊÇ·ñÕýÈ·¡£
ÐÞ¸Ä%windir%\my.ini£¬Ôö¼Ó
[mysqld]
#ÉèÖÃbasedirÖ¸ÏòmysqlµÄ°²×°Â·¾¶
basedir=D:\Program\Tools\mysql
datadir=D:\Program\Tools\mysql\data& ......
¸ßÐÔÄÜMySqlѧϰ±Ê¼Ç
1.Õë¶ÔÓ¦Óý¨Á¢×Ô¼ºµÄË÷Òý
URL²éÕÒÀý×Ó
select * from tUrl where url='http://www.163.com';
ÒÔurl£¨×Ö·û´®£©×÷ÐÐΪË÷Òý»áʹµÃ×÷ΪË÷Òý½á¹¹µÄB-Tree±ä´ó£¬¿ÉÒÔÒÆ³ýurlÁÐÉϵÄË÷Òý£¬²¢Ìí¼ÓÒ»¸öurl_crcË÷ÒýÁУ¬
ÏȽ¨Á¢±í£º
create tables tUrl(
......