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Tráön Nguyãn Phong ChChææåånngg 11:: NNGGÄÄNN NNGGÆÆÎÎ ÂÂËËNNHH NNGGHHÉÉAA DDÆÆÎÎ LLIIÃÃÛÛUU 1JQQJQKQJKDGOL£XEDRJPFDFFXO£QKFKRSKHSQJLVGX£QJQK QJKD&6'/YDFDF¢LW¤QJWURQJ&6'/QKFDFEDQJFDFNKXQJQKQFKPX£F 7DREDQJGOL
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Giaïo trçnh thæûc haình SQL • 7D£RQQWQKWRDQYH£QWK£FWKWURQJP¤WEDQJGOL£XYDWRDQYH£QWKDPFKL¢XJLD FDF EDQJ G OL£X WURQJ &6'/ UDQJ EX¤F 35,0$5< .(< 81,48( YD )25(,*1.(< &KXQJWDVHWPKLXFKLWL¢WKQYFDFUDQJEX¤FQD\SKQWUQKED\YFXO£QK &5($7(7$%/( 7DREDQJEQJWUX\YQ64/ 7D£RFDFEDQJODP¤WNKXTXDQWURQJWUR¤QJWURQJTXDWUQKWKL¢WN¢YDFDLG£W FDF&6'/%QWURQJFDF&6'/P¡LP¤WEDQJWKQJ¤FVGX£QJQKPELXGL¡Q WKQJWKLYFDF¢LW¤QJWURQJWK¢JLLWK£FYDKR£FELXGL¡QP¢LTXDQK£JLDFDF ¢LW¤QJRjFRWKWFKFW¢WP¤WEDQJGOL£XED£QWQK¢WFQSKDL[DFQK ¤FFDF\XFXVDX • %DQJ¤FVGX£QJQKPPX£FFKJYDFRYDLWURQKWK¢QDREQWURQJ&6'/" • %DQJVHEDRJPQKQJF¤WQDRYDNLXGOL£XFKRFDFF¤WRODJ" • 1KQJF¤WQDRFKRSKHSFK¢SQK£QJLDWU18// • &RVGX£QJFDFUDQJEX¤FFDFP£FQKKD\NKQJYDQ¢XFRWKVGX£QJXYD QKXWK¢QDR" • 1KQJF¤WQDRVHRQJYDLWURODNKRDFKQKNKRDQJRDLNKRDGX\QK¢W"1KQJ GD£QJFKPX£FQDRODFQWKL¢WYDFQX D7DREDQJGOL
X jWD£RP¤W EDQJ WURQJ &6'/ ED£Q V GX£QJ FX O£QK &5($7( 7$%/( FR FX SKDSQKVDX CREATE TABLE table_name ( {colname_1 col_1_properties [constraints_1 ] [,{colname_2 col_2_properties [constraints_2 ]] ... [,{colname_N col_N_properties [constraints_N ]] [table_constraints] ) 7URQJR - table_name: 7Q EDQJ FQ WD£R 7Q FXD EDQJ SKDL GX\ QK¢W WURQJP¡L&6'/YDSKDLWXQWKHRFDFTXLWFY QKGDQK - colname_i: 7QFXDF¤WWKLWURQJEDQJ&DFF¤WWURQJP¡L 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong EDQJSKDLFRWQNKDFQKDXYDSKDLWXQWKHRFDF TXL WF Y QK GDQK 0¡L P¤W EDQJ SKDL FR W QK¢WP¤WF¤W - col_i_properties: &DFWKX¤FWQKFXDF¤WWKLTXLQKNLXGOL£X FXD F¤W YD FK QK F¤W FR FKR SKHS FK¢S QK£Q JLDWU18//KD\NKQJ - constraints_i: &DF UDQJ EX¤F Q¢X FR WUQ F¤W WK L QK FDF UDQJEX¤FYNKRDFDFP£FQKFDFTXLQKY NKXQGD£QJGOL£X - table_constraint: &DFUDQJEX¤FWUQEDQJGOL£X 9GX&XO£QKGL\WK£FKL£QKYL£FWD£REDQJ1+$19,(1EDRJPFDFF¤W 0$19+27(11*$<6,1+',$&+,',(17+2$, CREATE TABLE nhanvien ( manv char(10) not null, hoten char(30) not null, ngaysinh datetime null, diachi char(50) null, dienthoai char(6) null ) E6GXQJFDFUDQJEXFWURQJEDQJGOL
X DDDD5DQJEXF&+(&. 5DQJEX¤F&+(&.¤FVGX£QJFKQKFDFJLDWUKD\NKXQGD£QJGOL£X FR WK ¤F FK¢S QK£Q ¢L YL P¤W F¤W 7UQ P¤W F¤W FR WK FR QKLX UDQJ EX¤F &+(&.jNKDLEDRP¤WUDQJEX¤F&+(&.¢LYLP¤WF¤WQDRRWDVGX£QJFX SKDSQKVDX [CONSTRAINT constraint_name] CHECK (expression) 7URQJRH[SUHVVLRQODP¤WELXWKFORJLFTXLQKJLDWUKD\NKXQGD£QJFXDG OL£X¤FFKRSKHS.KLRFKQKQJJLDWUGOL£XQDRODPFKRH[SUHVVLRQQK£QJLD WUXQJPL¤FFK¢SQK£Q 9GXjTXLQKL£QWKRD£LFXDQKQYLQSKDLFRGD£QJ FKQJ KD£Q FXO£QKYGX£¤FYL¢WQKVDX CREATE TABLE nhanvien ( ThiNganHang.com
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Giaïo trçnh thæûc haình SQL manv char(10) not null, hoten char(30) not null, ngaysinh datetime null, diachi char(50) null, dienthoai char(6) null constraint check_dienthoai check (dienthoai like '[0-9][0-9][0-9] [0-9][0-9] [0-9]') ) DDDD5DQJEXF'()$8/7 5DQJEX¤F'()$8/7¤FVGX£QJTXLQKJLDWUP£FQKFKRP¤WF¤W *LDWUQD\VHW£¤QJ¤FJDQFKRF¤WQD\NKLQJLVGX£QJE VXQJP¤WEDQJKL PDNKQJFKQKJLDWUFKR F¤W 7UQ P¡L F¤W FK FR WK FR QKLX QK¢W P¤W UDQJ EX¤F'()$8/7 WFODFKFRWKFRW¢LDP¤WJLDWUP£FQK j NKDL EDR P¤W JLD WU P£F QK FKR P¤W F¤W WD FK QK P¤W UDQJ EX¤F '()$8/7FKRF¤WEQJFDFKVGX£QJFXSKDSVDX [CONSTRAINT constraint_name] DEFAULT {const_expression nonarguments_function NULL} 9 GX &X O£QK GL \ FK QK JLD WU P£F QK OD NKQJ EL¢W FKR F¤W ',$&+,WURQJEDQJ1+$19,(1YGX£ CREATE TABLE nhanvien ( manv char(10) not null, hoten char(30) not null, ngaysinh datetime null, diachi char(50) default 'khäng biãút', dienthoai char(6) null ) DDDD5DQJEXF35,0$5<.(< muYGX£QD\FKXQJWLNKQJ£WWQFKRUDQJEX¤F'()$8/7.KLRK£TXDQWU&6'/VHW£¤QJ£WWQ FKRUDQJEX¤FQD\7X\QKLQG¡GDQJFKRYL£FTXDQWUED£QQQ£WWQFKRFDFUDQJEX¤F 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong 5DQJEX¤F35,0$5<.(<¤FVGX£QJQKQJKDNKRDFKQKFXDEDQJ 0¤WUDQJEX¤F35,0$5<.(< DPEDRUQJ NKQJ FR FDF JLD WU WUXQJ O£S ¤F DYDRWUQFDF F¤W +D\ QRL FDFK NKDF JLD WU FXD NKRD FKQK VH JLXS FKR WD [DF QK¤FGX\QK¢WP¤WGRQJ EDQJKL WURQJEDQJGOL£X0¡LP¤WEDQJFKFRWK FRGX\QK¢WP¤WNKRDFKQKYDEDQWKQNKRDFKQKNKQJFK¢SQK£QJLDWU18// 5DQJEX¤F35,0$5<.(<ODFVFKRYL£FDPEDRWQKWRDQYH£QWK£FWKFXQJ QKWRDQYH£QWKDPFKL¢X jNKDLEDRP¤WUDQJEX¤F35,0$5<.(<ED£QVGX£QJFXSKDSVDX [CONSTRAINT constraint_name ] PRIMARY KEY [CLUSTERED|NONCLUSTERED] [( colname [,colname2 [...,colname16]])] 1¢XNKRDFKQKFXDP¤WEDQJFKODP¤WF¤WNKLRED£QNKQJFQWKL¢WSKDLFK QKGDQKVDFKFDFF¤W VGX£QJUDQJEX¤FPFF¤W 7URQJWUQJK¤SNKRDFKQK ODP¤WW£SK¤SWKDLF¤WWUOQED£QSKDLFKQKGDQKVDFKFDFF¤W VGX£QJUDQJ EX¤FPFEDQJ 9GXWD£REDQJ1+$19,(1YLNKRDFKQKOD0$19 CREATE TABLE nhanvien ( manv char(10) primary key, hoten char(30) not null, ngaysinh datetime null, diachi char(50) null, dienthoai char(6) null ) FXO£QKWUQFRWKYL¢WQKVDX CREATE TABLE nhanvien ( manv char(10) not null, hoten char(30) not null, ngaysinh datetime null, diachi char(50) null, dienthoai char(6) null constraint pk_nv primary key(manv) ) ThiNganHang.com
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Giaïo trçnh thæûc haình SQL D 5DQJEXF81,48( 7KD\ Y V GX£QJ NKRD FKQK ED£Q FR WK V GX£QJ UDQJ EX¤F 81,48( DP EDRWQKWRDQYH£QWK£FWK6GX£QJUDQJEX¤F81,48(WUQP¤W KD\QKLX F¤WEW EX¤FFDFJLDWUGOL£XWUQP¤W KD\QKLX F¤WQD\NKQJ¤FWUXQJO£SQKDXj NKDLEDRP¤WUDQJEX¤F81,48(ED£QVGX£QJFXSKDSO£QKVDX\ [CONSTRAINT constraint_name] UNIQUE [CLUSTERED | NONCLUSTERED] [colname1 [,colname2 [...,colname16]])] D 5DQJEXF)25(,*1.(< &DFEDQJEQWURQJP¤W&6'/WKQJFRP¢LTXDQK£YLQKDX&DFP¢LTXDQ K£QD\¤F[DFQKG£DWUQWQK EQJQKDXJLDP¤WKD\QKLXWUQJFXD EDQJ QD\YLP¤WKD\QKLXWUQJFXDEDQJNKDF1¢XP¤W KD\QKLX F¤WQDRRFXDP¤W EDQJFRJLDWU¤F[DFQKWP¤W KD\QKLX WUQJNKRDFXDEDQJNKDFWKFDF F¤WR¤FJR¤LODFRUDQJEX¤FNKRDQJRD£L IRUHLJQNH\ &DFUDQJEX¤F)25(,*1 .(<¤FVGX£QJN¢WK¤SYLFDFUDQJEX¤F35,0$5<.(<YD81,48(QKP DPEDRWQKWRDQYH£QWKDPFKL¢XJLDFDFEDQJ¤FFKQK jNKDLEDRNKRDQJRD£LED£QVGX£QJFXSKDSO£QKQKVDX [CONSTRAINT constraint_name ] [FOREIGN KEY (colname [,colname2 [...,colname16]])] REFERENCES reference_table [(ref_colname [,ref_colname2 [...,ref_colname 16]])] 9 GX 7D£R KDL EDQJ 1+$19,(1 0$19 +27(1 1*$<6,1+ ',$&+, ',(17+2$,0$'9 YD'219, 0$'97(1'9 WKHRKQKGL\ 1+$19,(1 ∞∞∞∞ '219, 0$19 0$'9 +27(1 7(1'9 1*$<6,1+ ',$&+, ',(17+2$, 0$'9 +QK CREATE TABLE donvi ( 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong madv char(2) primary key, tendv char(20) not null ) CREATE TABLE nhanvien ( manv char(10) primary key, hoten char(20) not null, ngaysinh datetime null, diachi char(50) default 'khong biet', dienthoai char(6) check(dienthoai like '[0-9][0-9][0-9] [0-9][0-9][0-9]'), madv char(2) foreign key(madv) references donvi(madv) ) 6DLEDQJ 6DXNKLDWD£REDQJED£QFRWKWL¢QKDQKVDLF¢XWUXFKD\WKX¤FWQKFXD EDQJ QK E VXQJ F¤W E VXQJ NKRD WKD\ L FDF UDQJ EX¤F j FR WK VXD L EDQJED£QVGX£QJFXO£QK$/7(5FRFXSKDSQKVDX ALTER TABLE table_name [ADD {col_name column_properties [column_constraints] [[,]table_constraint ] } [,{next_col_name|next_table_constraint}]...] [DROP [CONSTRAINT] constraint_name1 [, constraint_name2]...] 9GX7D£RP¤WUDQJEX¤FFKREDQJ'219,WUQF¤W0$'9TXLQKPDQY SKDLFRGD£QJKDLFKV¢ YGX£ ALTER TABLE donvi ADD CONSTRAINT check_madv CHECK (madv LIKE ‘[0-9][0-9]’) ThiNganHang.com
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Giaïo trçnh thæûc haình SQL &KPXF LQGH[ &DFFKPX£F¤FVGX£QJQKPK¡WU¤YL£FWUX\F£S¢QFDFGRQJGOL£X¤F QKDQKFKRQJG£DWUQFDFJLDWUFXDP¤WKD\QKLXF¤W&KPX£F¤FFKLDUDODPKDL ORD£L FK PX£F WX£ QKRP FOXVWHUHG LQGH[ YD FK PX£F NKQJ WX£ QKRP QRQFOXVWHUHG LQGH[ • 0¤WFKPX£FWX£QKRPODP¤WFKPX£FPDWURQJRWKW£ORJLFFXDFDFNKRDWQJ W£QKWKW£Y£WO\FXDFDFGRQJWQJQJWQWD£LWURQJEDQJ0¤WEDQJFKFR WK FRW¢LDP¤WFKPX£FWX£QKRP • 0¤WFKPX£FNKQJWX£KRPODP¤WFKPX£FPDWURQJRWKW£ORJLFFXDFDFNKRD NKQJQKWKW£Y£WO\FXDFDFGRQJWURQJEDQJ&DFFKPX£FWX£QKRPK¡WU¤YL£F WUX\F£S¢QFDFGRQJGOL£XQKDQKKQQKLXVRYLFDFFKPX£FNKQJWX£QKRP .KLWDNKDLEDRP¤WNKRDFKQKKD\NKRD81,48(WUQP¤WKD\QKLXF¤WQDRR FXDEDQJK£TXDQWU&6'/VHW£¤QJWD£RFKPX£FWUQFDFF¤WR%D£QFRWKWD£R WKPFDFFKPX£FNKDFEQJFDFKVGX£QJFXO£QKFRFXSKDSQKVDX CREATE [CLUSTEREDNONCLUSTERED] INDEX index_name ON table_name(column_name [, column_name]...) 9GX&XO£QKGL\VHWD£RP¤WFKPX£FNKQJWX£QKRPWUQF¤W0$'9FXD EDQJ1+$19,(1 CREATE NONCLUSTERED INDEX idx_nhanvien_madv ON nhanvien(madv) .KXQJQKQ 9LHZ 0¤WNKXQJQKQFRWK FRLQKODP¤WeEDQJDRfFRQ¤LGXQJ¤F[DFQKW P¤W WUX\ Y¢Q 0¤W WUX\ Y¢Q TXHU\ OD P¤W W£S FDF FK G¡Q LQVWUXFWLRQ QKP WUX\ [X¢WYDKLQWKGOL£XWFDFEDQJWURQJ&6'/&DFWUX\Y¢Q¤FWK£FKL£QEQJ FDFKVGX£QJFXO£QK6(/(&7 ¤FF£S¢QWURQJFKQJ 0¤WNKXQJQKQWURQJJL¢QJQKP¤WEDQJYLP¤WW£RFDFWQF¤WYDFDFGRQJ GOL£X7X\QKLQNKXQJQKQNKQJWQWD£LQKODP¤WF¢XWUXFOXWUGOL£XWURQJ &6'/'OL£XEQWURQJNKXQJQKQWK£FFK¢WODGOL£X¤F[DFQKWP¤WKD\ QKLXEDQJFVYDGRRSKX£WK¤FYDRFDFEDQJFV &DFNKXQJQKQWKQJ¤FVGX£QJEQWURQJ&6'/QKPFDFPX£FFKVDX \ • 6GX£QJNKXQJQKQW£SWUXQJWUQGOL£X¤F[DFQK 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong • 6GX£QJNKXQJQKQQJLDQKRDWKDRWDFGOL£X • 6GX£QJNKXQJQKQWX\EL¢QGOL£X • 6GX£QJNKXQJQKQ[X¢WNKX H[SRUW GOL£X • 6GX£QJNKXQJQKQEDRP£WGOL£X jWD£RNKXQJQKQED£QVGX£QJFXO£QKFRFXSKDSQKVDX CREATE VIEW view_name[(column_name [, column_name]...)] AS select_statement 7URQJRVHOHFWBVWDWHPHQWODP¤WFXO£QK6(/(&7GXQJWUX\[X¢WGOL£XW P¤WKD\QKLXEDQJ .KLWD£RNKXQJQKQFQOX\P¤WV¢LPVDX • 7QNKXQJQKQSKDLWXQWKHRFDFTXLWFYQKGDQKYDSKDLGX\QK¢W¢LYL P¡LQJLVGX£QJ • .KQJWKUDQJEX¤FFDFP£FQKFDFTXLWFFKRNKXQJQKQ • .KQJWK[\G£QJFKPX£FFKRNKXQJQKQ • 7URQJFXO£QK&5($7( 9,(:NKQJFQ WKL¢W SKDL FK QK WQ F¤W 7Q FXD FDFF¤WFXQJQKNLXGOL£XFXDFKXQJVHWQJQJYLFDFF¤WWURQJGDQKVDFK FKR¤QFXDFXO£QK6(/(&7 • %D£QSKDL[DFQKWQF¤WWURQJFX O£QK&5($7( 9,(:WURQJFDFWUQJK¤S VDX − 0¡LF¤WFXDNKXQJQKQ¤FSKDWVLQKWP¤WELXWKFV¢KR¤FP¤WKDPFDL VQKD\P¤WKQJ − +DLKD\QKLXF¤WFXDNKXQJQKQFRWUXQJWQ − %D£QPX¢QWKD\LWQF¤WWURQJNKXQJQKQNKDFYLWQF¤WFXDEDQJFV 9GX&XO£QKGL\VHEO¡LGRWQFXDF¤WWKNKQJ[DFQK¤F CREATE VIEW thongtin_nv AS SELECT manv,hoten,datediff(year,ngaysinh,getdate()),tendv FROM nhanvien,donvi WHERE nhanvien.madv=donvi.madv jFXO£QKWUQFRWKWK£FKL£Q¤FED£QSKDL£WWQFKRFDFF¤WFXDNKXQJQKQ QKVDX CREATE VIEW thongtin_nv(manv,hoten,tuoi,donvi) ThiNganHang.com
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Giaïo trçnh thæûc haình SQL AS SELECT manv,hoten,datediff(year,ngaysinh,getdate()),tendv FROM nhanvien,donvi WHERE nhanvien.madv=donvi.madv Z Y 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong ChChææåånngg 22:: NNGGÄÄNN NNGGÆÆÎÎ TTHHAAOO TTAAÏÏCC DDÆÆÎÎ LLIIÃÃÛÛUU 1JQQJWKDRWDFGOL£XFXQJF¢SFKRQJLVGX£QJNKDQQJWL¢QKDQKFDF WKDRWDFWUX\[X¢WEVXQJF£SQK£WYD[RDGOL£X1JQQJWKDRWDFGOL£XEDR JPFDFFXO£QK6(/(&7,16(5783'$7(YD'(/(7( 7UX\[XWGOL
X §Ó truy xuÊt d÷ liÖu tõ c¸c dßng vμ c¸c cét cña mét hay nhiÒu b¶ng, khung nh×n, ta sö dông c©u lÖnh SELECT. C©u lÖnh nμy cã thÓ dïng ®Ó thùc hiÖn phÐp chän (tøc lμ truy xuÊt mét tËp con c¸c dßng trong mét hay nhiÒu b¶ng), phÐp chiÕu (tøc lμ truy xuÊt mét tËp con c¸c cét trong mét hay nhiÒu b¶ng) vμ phÐp nèi (tøc lμ liªn kÕt c¸c dßng trong hai hay nhiÒu b¶ng ®Ó truy xuÊt d÷ liÖu). Có ph¸p chung cña c©u lÖnh SELECT cã d¹ng nh sau: SELECT [ ALL | DISTINCT ] select_list [ INTO [ newtable_name ]] FROM { table_name | view_name } ................ [,{table_name | view_name }] [WHERE clause ] [GROUP BY clause ] [HAVING BY clause ] [ORDER BY clause ] [COMPUTE clause ] Chó ý: C¸c thμnh phÇn trong mét c©u lÖnh SELECT ph¶i ® îc sö dông theo thø tù ® îc nªu trªn. 1.1 X¸c ®Þnh b¶ng b»ng mÖnh ®Ò FROM MÖnh ®Ò FROM trong c©u lÖnh SELECT ® îc sö dông nh»m chØ ®Þnh c¸c b¶ng vμ khung nh×n cÇn truy xuÊt d÷ liÖu. Sau mÖnh ®Ò FROM lμ danh s¸ch tªn c¸c b¶ng vμ khung nh×n tham gia vμo truy vÊn (tªn cña c¸c b¶ng vμ khung nh×n ® îc ph©n c¸ch nhau bëi dÊu phÈy). SELECT select_list FROM {table_nameview_name list} ThiNganHang.com
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Giaïo trçnh thæûc haình SQL §Ó ®¬n gi¶n ho¸ c©u hái, ta cã thÓ sö dông c¸c bÝ danh (alias) cho c¸c b¶ng hay khung nh×n. BÝ danh ® îc g¸n trong mÖnh ®Ò FROM b»ng c¸ch chØ ®Þnh bÝ danh sau tªn b¶ng. VÝ dô c©u lÖnh sau g¸n bÝ danh n1 cho b¶ng nhanvien. SELECT ten, diachi FROM nhanvien n1 1.2 MÖnh ®Ò WHERE MÖnh ®Ò WHERE trong c©u lÖnh SELECT x¸c ®Þnh c¸c ®iÒu kiÖn ®èi víi viÖc truy xuÊt d÷ liÖu. Sau mÖnh ®Ò WHERE lμ mét biÓu thøc logic vμ chØ nh÷ng dßng d÷ liÖu nμo tho¶ m∙n biÓu thøc sau WHERE míi ® îc hiÓn thÞ trong kÕt qu¶ truy vÊn. Trong mÖnh ®Ò WHERE th êng sö dông: • C¸c to¸n tö so s¸nh • Giíi h¹n ( BETWEEN vμ NOT BETWEEN). • Danh s¸ch (IN, NOT IN) • Khu«n d¹ng (LIKE vμ NOT LIKE). • C¸c gi¸ trÞ ch a biÕt (IS NULL vμ IS NOT NULL). • KÕt hîp c¸c ®iÒu kiÖn (AND, OR). C¸c to¸n tö so s¸nh: To¸n tö ý nghÜa = B»ng > Lín h¬n < Nhá h¬n >= Lín h¬n hoÆc b»ng <= Nhá h¬n hoÆc b»ng <> Kh¸c !> Kh«ng lín h¬n !< Kh«ng nhá h¬n VÝ dô 2.1: Truy vÊn sau ®©y cho biÕt tªn, ®Þa chØ vμ ®iÖn tho¹i cña nh÷ng nh©n viªn cã hÕ sè l ¬ng lín h¬n 1.92: SELECT ten, diachi, dienthoai FROM nhanvien WHERE hsluong>1.92 Giíi h¹n (BETWEEN vμ NOT BETWEEN) Tõ kho¸ BETWEEN vμ NOT BETWEEN ® îc sö dông nh»m chØ ®Þnh kho¶ng gi¸ trÞ t×m kiÕm ®èi víi c©u lÖnh SELECT. C©u lÖnh d íi ®©y cho biÕt tªn vμ ®ia chØ cña nh÷ng nh©n viªn cã hÖ sè l ¬ng n»m trong kho¶ng 1.92 ®Õn 3.11 SELECT ten, tuoi, diachi FROM nhanvien WHERE hsluong BETWEEN 1.92 AND 3.11 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong Danh s¸ch (IN vμ NOT IN) Tõ kho¸ IN ® îc sö dông khi ta cÇn chØ ®Þnh ®iÒu kiÖn t×m kiÕm d÷ liÖu cho c©u lÖnh SELECT lμ mét danh s¸ch c¸c gi¸ trÞ. Sau IN (hoÆc NOT IN) cã thÓ lμ mét danh s¸ch c¸c gi¸ trÞ hoÆc lμ mét c©u lÖnh SELECT kh¸c. VÝ dô 2.2: §Ó hiÓn thÞ th«ng tin vÒ c¸c nh©n viªn cã hÖ sè l ¬ng lμ 1.86, 1.92 hoÆc 2.11, thay v× sö dông c©u lÖnh: SELECT * FROM nhanvien WHERE hsluong=1.86 OR hsluong=1.92 OR hsluong=2.11 Ta cã thÓ sö dông c©u lÖnh sau: SELECT * FROM nhanvien WHERE hsluong IN (1.86, 1.92, 2.11) C¸c ký tù ®¹i diÖn vμ mÖnh ®Ò LIKE Tõ kho¸ LIKE (NOT LIKE) sö dông trong c©u lÖnh SELECT nh»m m« t¶ khu«n d¹ng cña d÷ liÖu cÇn t×m kiÕm. Chóng th êng ® îc kÕt hîp víi c¸c ký tù ®¹i diÖn sau ®©y: Ký tù ®¹i diÖn ý nghÜa % Chuçi ký tù bÊt kú gåm kh«ng hoÆc nhiÒu ký tù - Ký tù ®¬n bÊt kú [] Ký tù ®¬n bÊt kú trong giíi h¹n ® îc chØ ®Þnh (vÝ dô [a-f]) hay mét tËp (vÝ dô [abcdef]) [^] Ký tù ®¬n bÊt kú kh«ng n»m trong giíi h¹n ® îc chØ ®Þnh ( vÝ dô [^a-f] hay mét tËp (vÝ dô [^abcdef]). VÝ dô 2.3: C©u lÖnh d íi ®©y hiÓn thÞ th«ng tin vÒ c¸c nh©n viªn cã tªn lμ Nam SELECT * FROM nhanvien WHERE hoten LIKE '% Nam' IS NULL vμ NOT IS NULL Gi¸ trÞ NULL cã thÓ ® îc nhËp vμo mét cét cho phÐp chÊp nhËn gi¸ trÞ NULL theo mét trong ba c¸ch sau: • NÕu kh«ng cã d÷ liÖu ® îc ® a vμo vμ kh«ng cã mÆc ®Þnh cho cét hay kiÓu d÷ liÖu trªn cét ®ã. • Ng êi sö dông trùc tiÕp ® a gi¸ trÞ NULL vμo cho cét ®ã. • Mét cét cã kiÓu d÷ liÖu lμ kiÓu sè sÏ chøa gi¸ trÞ NULL nÕu gi¸ trÞ ® îc chØ ®Þnh g©y trμn sè. Trong mÖnh ®Ò WHERE, ta sö dông IS NULL hoÆc IS NOT NULL nh sau: WHERE col_name IS [NOT] NULL C¸c to¸n tö logic C¸c to¸n tö logic sö dông trong mÖnh ®Ò WHERE bao gåm AND, OR, NOT. AND vμ OR ® îc sö dông ®Ó kÕt hîp nhiÒu ®iÒu kiÖn trong WHERE. 1.3 Danh s¸ch chän trong c©u lÖnh SELECT ThiNganHang.com
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Giaïo trçnh thæûc haình SQL &Kän tÊt c¶ c¸c cét trong b¶ng Khi muèn truy xuÊt tÊt c¶ c¸c cét trong b¶ng, ta sö dông c©u lÖnh SELECT cã có ph¸p sau: SELECT * FROM table_name Khi sö dông c©u lÖnh nμy, c¸c cét trong kÕt qu¶ sÏ ® îc hiÓn thÞ theo thø tù mμ chóng ®∙ ® îc t¹o ra trong c©u lÖnh CREATE TABLE. * Chän c¸c cét ® îc chØ ®Þnh §Ó chän ra mét sè cét nμo ®ã trong b¶ng, ta sö dông c©u lÖnh SELECT cã có ph¸p sau: SELECT tªn_cét [,...,tªn_cét_n] FROM tªn_b¶ng | khung_nh×n C¸c tªn cét trong c©u lÖnh ph¶i ® îc ph©n c¸ch nhau b»ng dÊu phÈy. Chó ý: Trong c©u lÖnh SELECT, thø tù cña c¸c cét ® îc nªu ra trong c©u lÖnh sÏ x¸c ®Þnh thø tù cña c¸c cét ® îc hiÓn thÞ ra trong kÕt qu¶. * §æi tªn c¸c cét trong c¸c kÕt qu¶ Khi kÕt qu¶ ® îc hiÓn thÞ, tiªu ®Ò cña c¸c cét mÆc ®Þnh sÏ lμ tªn cña c¸c cét khi nã ® îc t¹o ra trong c©u lÖnh CREATE TABLE. Tuy nhiªn, ®Ó c¸c tiªu ®Ò trë nªn th©n thiÖn h¬n, ta cã thÓ ®æi tªn c¸c tiªu ®Ò cña c¸c cét. §Ó lμm ® îc viÖc nμy, ta cã thÓ sö dông mét trong hai c¸ch viÕt sau: tiªu_®Ò_cét = tªn_cét hoÆc tªn_cét tiªu_®Ò_cét VÝ dô 2.4: Hai c©u lÖnh sau sÏ ®Æt tiªu ®Ò Hä vμ tªn cho lμ hoten vμ §Þa chØ cho cét diachi khi kÕt qu¶ ® îc hiÓn thÞ cho ng êi sö dông: SELECT 'Hä vμ tªn'=hoten, '§Þa chØ '= diachi FROM nhanvien HoÆc: SELECT hoten 'Hä vμ tªn',diachi '§ia chØ ' FROM nhanvien * Sö dông cÊu tróc CASE ®Ó thay ®æi d÷ liÖu trong kÕt qu¶ Trong c©u lÖnh SELECT, ta cã thÓ sö dông cÊu tróc CASE ®Ó thay ®æi c¸ch hiÓn thÞ kÕt qu¶ ra mμn h×nh. VÝ dô 2.5: C©u lÖnh sau cho biÕt hä tªn, hÖ sè l ¬ng vμ xÕp lo¹i l ¬ng cña nh©n viªn theo hÖ sè l ¬ng: SELECT 'Hä vμ tªn' = ten, 'HÖ sè l ¬ng' = hsluong, 'XÕp lo¹i l ¬ng' = CASE WHEN lsluong=NULL THEN 'Kh«ng x¸c ®Þnh' 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong WHEN hsluong<=1.92 THEN 'Lu¬ng thÊp' WHEN hsluong<=3.1 THEN 'L ¬ng TB' WHEN hsluong<=5.2 THEN 'L ¬ng cao' ELSE 'L ¬ng rÊt cao' END FROM Nhanvien * C¸c chuçi ký tù trong kÕt qu¶ Ta cã thÓ thªm c¸c chuçi ký tù vμo bªn trong truy vÊn nh»m thay ®æi c¸ch thøc tr×nh bμy d÷ liÖu. VÝ dô 2.6: C©u lÖnh sau sÏ thªm chuçi ký tù “HÖ sè l ¬ng lμ “ vμo tr íc kÕt qu¶ ë cét møc l ¬ng ë tõng dßng trong kÕt qu¶: SELECT 'Hä vμ tªn' = hoten, 'HÖ sè l ¬ng lμ : ','HÖ sè l ¬ng'=hsluong FROM nhanvien Truy vÊn trªn cho cã kÕt qu¶ cã d¹ng nh sau: Hä vμ tªn HÖ sè l ¬ng ---------------- -------------- ------------- TrÇn Nguyªn Phong HÖ sè l ¬ng lμ : 1.92 Lª Hoμi Nam HÖ sè l ¬ng lμ : 1.86 NguyÔn H÷u T×nh HÖ sè l ¬ng lμ : 1.92 NguyÔn Trung Kiªn HÖ sè l ¬ng lμ : 1.86 NguyÔn ThÞ Hoa HÖ sè l ¬ng lμ : 2.11 Hoμng Nam Phong HÖ sè l ¬ng lμ : 3.21 1.4 TÝnh to¸n c¸c gi¸ trÞ trong c©u lÖnh SELECT Danh s¸ch chän trong c©u lÖnh SELECT cã thÓ cã c¸c biÓu thøc sè häc. Khi ®ã kÕt qu¶ cña biÓu thøc sÏ lμ mét cét trong kÕt qu¶ truy vÊn: VÝ dô 2.7: C©u lÖnh sau cho biÕt hä tªn vμ l ¬ng cña c¸c nh©n viªn SELECT 'Hä vμ tªn'=ten, 'L ¬ng'=hsluong*210000 FROM nhanvien 1.5 Tõ kho¸ DISTINCT Tõ kho¸ DISTINCT ® îc sö dông trong c©u lÖnh SELECT nh»m lo¹i bá ra khái kÕt qu¶ truy vÊn nh÷ng dßng d÷ liÖu cã gi¸ trÞ gièng nhau VÝ dô 2.8: nÕu ta sö dông c©u lÖnh: SELECT hsluong FROM nhanvien Ta sÏ cã kÕt qu¶ nh sau: ThiNganHang.com
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Giaïo trçnh thæûc haình SQL hsluong ----------------- 1.92 1.86 1.92 1.86 2.11 3.21 Nh ng nÕu ta sö dông c©u lÖnh: SELECT DISTINCT hsluong FROM nhanvien kÕt qu¶ cña truy vÊn sÏ lμ: hsluong ---------- 1.92 1.86 2.11 3.21 1.6 T¹o b¶ng míi b»ng c©u lÖnh SELECT ... INTO C©u lÖnh SELECT ... INTO cã t¸c dông t¹o mét b¶ng míi cã cÊu tróc vμ d÷ liÖu ® îc x¸c ®Þnh tõ kÕt qu¶ cña truy vÊn. B¶ng míi ® îc t¹o ra sÏ cã sè cét b»ng sè cét ® îc chØ ®Þnh trong danh s¸ch chän vμ sè dßng sÏ μ sè dßng kÕt qu¶ cña truy vÊn VÝ dô 2.9: C©u lÖnh d íi ®©y t¹o míi mét b¶ng cã tªn lμ NHANVIEN_LUU bao gåm hä tªn vμ ®Þa chØ cña nh÷ng nh©n viªn cã hÖ sè l ¬ng lín h¬n 1.92: SELECT hoten, diachi INTO nhanvien_luu FROM nhanvien WHERE hsluong>1.92 1.7 S¾p xÕp kÕt qu¶ truy vÊn b»ng ORDER BY MÖnh ®Ò ORDER BY ® îc sö dông nh»m s¾p xÕp kÕt qu¶ truy vÊn theo mét hay nhiÒu cét (tèi ®a lμ 16 cét). ViÖc s¾p xÕp cã thÓ theo thø tù t¨ng t¨ng (ASC) hoÆc gi¶m (DESC). NÕu kh«ng chØ ®Þnh râ th× mÆc ®Þnh lμ t¨ng. VÝ dô 2.10: C©u lÖnh sau sÏ s¾p xÕp c¸c nh©n viªn theo thø tù gi¶m dÇn cña hÖ sè l ¬ng vμ nÕu hÖ sè l ¬ng b»ng nhau th× s¾p xÕp theo thø tù t¨ng dÇn cña ngμy sinh: SELECT hoten,ngaysinh,hsluong FROM nhanvien ORDER BY hsluong DESC, ngaysinh Ta cã thÓ sö dông c¸c sè thay v× sö dông tªn cét sau mÖnh ®Ò ORDER BY. VÝ dô 2.11: c©u lÖnh d íi ®©y s¾p xÕp c¸c nh©n viªn theo thø tù t¨ng dÇn cña ngμy sinh: 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong SELECT hoten,ngaysinh,hsluong FROM nhanvien ORDER BY 3 1.8 PhÐp hîp vμ to¸n tö UNION To¸n tö UNION cho phÐp ta hîp c¸c kÕt qu¶ cña hai hay nhiÒu truy vÊn thμnh mét tËp kÕt qu¶ duy nhÊt. Có ph¸p cña phÐp hîp nh sau: Query_1 [UNION [ALL] Query_2 ] ... [UNION [ALL] Query_N ] [ORDER BY clause] [COMPUTE clause] Trong ®ã: Query_1 cã d¹ng: SELECT select_list [INTO clause] [FROM clause] [WHERE clause] [GROUP BY clause] [HAVING clause] vμ Query_i (i=2,..,N) cã d¹ng: SELECT select_list [FROM clause] [WHERE clause] [GROUP BY clause] [HAVING clause] VÝ dô 2.12: Gi¶ sö ta cã hai b¶ng nh sau: R S A B C E F abc 3 5 edf 15 jks 5 7 hht 1 bdg 10 5 abc 3 Hht 12 0 adf 2 Th× phÐp hîp: SELECT A,B FROM R UNION ThiNganHang.com
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Giaïo trçnh thæûc haình SQL SELECT * FROM S Cã kÕt qu¶ nh sau: A B ---- ----------- abc 3 adf 2 bgd 10 edf 15 hht 1 hht 12 jks 5 Theo mÆc ®Þnh, phÐp to¸n UNION sÏ lo¹i bá nh÷ng dßng gièng nhau trong kÕt qu¶. NÕu ta sö dông tïy chän ALL th× c¸c dßng gièng nhau sÏ kh«ng bÞ lo¹i bá. Ta cã thÓ sö dông c¸c dÊu ngoÆc ®Ó x¸c ®Þnh thø tù tÝnh to¸n trong phÐp hîp. 1.8.1 C¸c nguyªn t¾c khi x©y dùng c©u lÖnh UNION Khi x©y dùng c¸c c©u lÖnh UNION, ta cÇn chó ý c¸c nguyªn t¾c sau: • TÊt c¶ c¸c danh s¸ch chän trong c©u lÖnh UNION ph¶i cã cïng sè biÓu thøc (c¸c tªn cét, c¸c biÓu thøc sè häc, c¸c hμm gép,...) • C¸c cét t ¬ng øng trong tÊt c¶ c¸c b¶ng, hoÆc tËp con bÊt kú c¸c cét ® îc sö dông trong b¶n th©n mçi truy vÊn ph¶i cïng kiÓu d÷ liÖu. • C¸c cét t ¬ng øng trong b¶n th©n tõng truy vÊn cña mét c©u lÖnh UNION ph¶i xuÊt hiÖn theo thø tù nh nhau. Nguyªn nh©n lμ do phÐp hîp so s¸nh c¸c cét tõng cét mét theo thø tù ® îc cho trong mçi truy vÊn. • Khi c¸c kiÓu d÷ liÖu kh¸c nhau ® îc kÕt hîp víi nhau trong c©u lÖnh UNION, chóng sÏ ® îc chuyÓn sang kiÓu d÷ liÖu cao h¬n (nÕu cã thÓ ® îc). • Tiªu ®Ò cét trong kÕt qu¶ cña phÐp hîp sÏ lμ tiªu ®Ò cét ® îc chØ ®Þnh trong truy vÊn ®Çu tiªn. 1.8.2 Sö dông UNION víi c¸c giao t¸c SQL kh¸c C¸c nguyªn t¾c sau ph¶i ® îc tu©n theo khi sö dông phÐp hîp víi c¸c c©u lÖnh giao t¸c SQL kh¸c: • Truy vÊn ®Çu tiªn trong c©u lÖnh UNION cã thÓ cã INTO ®Ó t¹o mét b¶ng tõ kÕt qu¶ cuèi cïng. • MÖnh ®Ò ORDER BY vμ COMPUTE dïng ®Ó x¸c ®Þnh thø tù kÕt qu¶ cuèi cïng hoÆc tÝnh to¸n c¸c gi¸ trÞ tãm t¾t chØ ® îc cho phÐp sö dông ë cuèi cña c©u lÖnh UNION. Chóng kh«ng ® îc phÐp sö dông trong bÊt kú b¶n th©n truy vÊn nμo trong phÐp hîp. • MÖnh ®Ò GROUP BY vμ HAVING chØ cã thÓ ® îc sö dông trong b¶n th©n tõng truy vÊn. Chóng kh«ng thÓ ® îc sö dông ®Ó t¸c ®éng lªn kÕt qu¶ cuèi cïng. 7UDQJ ThiNganHang.com
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Tráön Nguyãn Phong • PhÐp to¸n UNION còng cã thÓ ® îc sö dông bªn trong mét c©u lÖnh INSERT. • PhÐp to¸n UNION kh«ng thÓ sö dông trong c©u lÖnh CREATE VIEW. 1.9 PhÐp nèi PhÐp nèi ® îc sö dông ®Ó truy xuÊt d÷ liÖu tõ hai hay nhiÒu b¶ng hoÆc khung nh×n trong cïng CSDL hoÆc trong c¸c CSDL kh¸c nhau bëi cïng mét phÐp xö lý. 1.9.1 PhÐp to¸n nèi Mét c©u lÖnh nèi (join statament) thùc hiÖn c¸c c«ng viÖc sau ®©y: • X¸c ®Þnh mét cét tõ mçi b¶ng. • So s¸nh c¸c gi¸ trÞ trong nh÷ng cét nμy theo tõng dßng. • KÕt hîp c¸c dßng cã nh÷ng gi¸ trÞ tho¶ m∙n ®iÒu kiÖn thμnh nh÷ng dßng míi. VÝ dô 2.13: C©u lÖnh d íi ®©y cho biÕt hä tªn, ®Þa chØ cña c¸c nh©n viªn vμ tªn ®¬n vÞ mμ mçi nh©n viªn thùc thuéc: SELECT hoten, diachi, tendonvi FROM nhanvien, donvi WHERE nhanvien.madonvi = donvi.madonvi Danh s¸ch chän trong phÐp nèi Gièng nh c¸c c©u lÖnh chän (selection statment), mét c©u lÖnh nèi b¾t ®Çu víi tõ khãa SELECT. C¸c cét ® îc chØ ®Þnh tªn sau tõ kho¸ SELECT lμ c¸c cét ® îc d a ra trong kÕt qu¶ truy vÊn. Trong danh s¸ch chän cña phÐp nèi, ta cã thÓ chØ ®Þnh mét sè cét b»ng c¸ch chØ ®Þnh tªn cña cét ®ã hoÆc tÊt c¶ c¸c cét cña nh÷ng b¶ng tham gia vμo phÐp nèi b»ng c¸ch sö dông dÊu sao (*). Danh s¸ch chän kh«ng nhÊt thiÕt ph¶i bao gåm c¸c cét cña nh÷ng b¶ng tham gia phÐp nèi. MÖnh ®Ò FROM trong phÐp nèi MÖnh ®Ò FROM cña c©u lÖnh nèi x¸c dÞnh c¸c b¶ng (hay khung nh×n) tham gia vμo phÐp nèi. NÕu ta sö dông dÊu * trong danh s¸ch chän th× thø tù cña c¸c b¶ng liÖt kª trong FROM sÏ ¶nh h ëng ®Õn kÕt qu¶ ® îc hiÓn thÞ. MÖnh ®Ò WHERE trong phÐp nèi MÖnh ®Ò WHERE x¸c ®Þnh ®iÒu kiÖn nèi gi÷a c¸c b¶ng vμ c¸c khung nh×n ® îc chØ ®Þnh. Nã x¸c ®Þnh tªn cña cét ® îc sö dông ®Ó nèi vμ phÐp to¸n nèi ® îc sö dông. C¸c to¸n tö so s¸nh d íi ®©y ® îc sö dông ®Ó x¸c ®Þnh ®iÒu kiÖn nèi PhÐp to¸n ý nghÜa = B»ng > Lín h¬n >= Lín h¬n hoÆc b»ng < Nhá h¬n <= Nhá h¬n hoÆc b»ng <> Kh¸c ThiNganHang.com
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