SQL distinctÓ÷¨¡¡¼òµ¥group by ÃüÁî
distinctÕâ¸ö¹Ø¼ü×ÖÓÃÀ´¹ýÂ˵ô¶àÓàµÄÖØ¸´¼Ç¼ֻ±£ÁôÒ»Ìõ£¬µ«ÍùÍùÖ»ÓÃËüÀ´·µ»Ø²»Öظ´¼Ç¼µÄÌõÊý£¬¶ø²»ÊÇÓÃËüÀ´·µ»Ø²»ÖؼǼµÄËùÓÐÖµ¡£ÆäÔÒòÊÇdistinctÖ»ÓÐÓöþÖØÑ»·²éѯÀ´½â¾ö£¬¶øÕâÑù¶ÔÓÚÒ»¸öÊý¾ÝÁ¿·Ç³£´óµÄÕ¾À´Ëµ£¬ÎÞÒÉÊÇ»áÖ±½ÓÓ°Ï쵽ЧÂʵġ£
ÏÂÃæÏÈÀ´¿´¿´Àý×Ó£º
table±í
×Ö¶Î1 ×Ö¶Î2
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£¬ÄǾͱØÐë
ʹÓÃdistinctÈ¥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
ÎÒÃÇÔٸĸIJéѯÓï¾ä:
select id, distinct name from table
ºÜÒź¶£¬³ýÁË´íÎóÐÅÏ¢ÄãʲôҲµÃ²»µ½£¬distinct±ØÐë·ÅÔÚ¿ªÍ·¡£Äѵ½²»ÄܰÑdistinct·Åµ½whereÌõ¼þÀÄÜ£¬ÕÕÑù±¨´í¡£
--------------------------------------------------------
ÏÂÃæ·½·¨¿ÉÐÐ:
select *, count(distinct name) from table group by name
½á¹û:
id name count(distinct name)
1 a 1
2 b 1
3 c 1
×îºóÒ»ÏîÊǶàÓàµÄ£¬²»ÓùܾÍÐÐÁË£¬Ä¿µÄ´ïµ½
group by ±ØÐë·ÅÔÚ order by ºÍ limit֮ǰ£¬²»È»»á±¨´í
Ïà¹ØÎĵµ£º
SQL Server 7.0 ÈëÃÅ(7)
ʱ¼ä£º2001/02/06 11:57 ×÷Õߣº¶¹¶¹ CHINAASP
¡¡ &nbs ......
char¡¢varchar¡¢textºÍnchar¡¢nvarchar¡¢ntext
charºÍvarcharµÄ³¤¶È¶¼ÔÚ1µ½8000Ö®¼ä£¬ËüÃǵÄÇø±ðÔÚÓÚcharÊǶ¨³¤×Ö·ûÊý¾Ý£¬¶øvarcharÊDZ䳤×Ö·ûÊý¾Ý¡£Ëùν¶¨³¤¾ÍÊdz¤¶È¹Ì¶¨
µÄ£¬µ±ÊäÈëµÄÊý¾Ý³¤¶ÈûÓдﵽָ¶¨µÄ³¤¶Èʱ½«×Ô¶¯ÒÔÓ¢ÎĿոñÔÚÆäºóÃæÌî³ä£¬Ê¹³¤¶È´ïµ½ÏàÓ¦µÄ³¤¶È£»¶ø±ä ......
¾ßÓй̶¨ÓÐЧλÊýºÍСÊýλÊýµÄÊýÖµ×ÊÁÏÀàÐÍ¡£
decimal[ (p[ , s] )] and numeric[ (p[ , s] )]
¹Ì¶¨ÓÐЧλÊýºÍСÊýλÊýµÄÊý×Ö¡£µ±Ê¹ÓÃ×î´óÓÐЧλÊýʱ£¬ÓÐЧֵÊÇ´Ó - 10^38 +1 µ½ 10^38 - 1¡£decimal µÄ SQL-92 ͬÒå×ÖÊÇ dec ºÍ dec(p, s)¡£numeric µÄ¹¦ÄÜÏàµ±ì¶ decimal¡£
p (ÓÐЧλÊý)
¿É´¢´æµÄ×î´óÊ®½øÎ»Êý×ÜÊý£¬Ð¡ ......
ÔÚ½éÉÜGROUP BY ºÍ HAVING ×Ó¾äǰ£¬ÎÒÃDZØÐèÏȽ²½²sqlÓïÑÔÖÐÒ»ÖÖÌØÊâµÄº¯Êý£º¾ÛºÏº¯Êý£¬ÀýÈçSUM, COUNT, MAX, AVGµÈ¡£ÕâЩº¯ÊýºÍÆäËüº¯ÊýµÄ¸ù±¾Çø±ð¾ÍÊÇËüÃÇÒ»°ã×÷ÓÃÔÚ¶àÌõ¼Ç¼ÉÏ¡£
SELECT SUM(population) from bbc
¡¡¡¡ÕâÀïµÄSUM×÷ÓÃÔÚËùÓзµ»Ø¼Ç¼µÄpopulation×Ö¶ÎÉÏ£¬½á¹û¾ÍÊǸòéѯֻ·µ»ØÒ»¸ö½á¹û£¬¼´ËùÓйú¼ÒµÄ× ......
SQL Server 2005 Express µ¼Èë/µ¼³öÊý¾Ý
°²×°ºÃSQL Server 2005 Expressºó£¬ÔÙ°²×°
http://download.microsoft.com/download/1/1/0/110d908f-c445-4523-b939-220c7d135f3d/SQLServer2005_SSMSEE.msi
¾Í¿ÉÒÔʹÓÿØÖÆÌ¨½øÐÐÊý¾Ý¿âµÄ¹ÜÀí¡£
µ«SQL Server Management Studio Express ²¢Ã»Óе¼Èë/µ¼³öÊý¾ÝµÄ¹¦ÄÜ£¬ÎÒÃÇ¿ÉÒÔ ......