1.delphi中操作access數據庫(建立.mdb文件,壓縮數據庫)
以下代碼在win2k,d6,mdac2.6下測試通過,
編譯好的程序在win98第二版無access環境下運行成功.
//在之前uses comobj,activex
//聲明連接字符串
const
sconnectionstring = 'provider=microsoft.jet.oledb.4.0;data source=%s;'
+'jet oledb:database password=%s;';
//=============================================================================
// procedure: gettemppathfilename
// author : ysai
// date : 2003-01-27
// arguments: (none)
// result : string
//=============================================================================
function gettemppathfilename():string;
//取得臨時文件名
var
spath,sfile&:array [0..254] of char;
begin
gettemppath(254,spath);
gettempfilename(spath,'~sm',0,sfile);
result:=sfile;
deletefile(pchar(result));
end;
//=============================================================================
// procedure: createaccessfile
// author : ysai
// date : 2003-01-27
// arguments: filename:string;password:string=''
// result : boolean
//=============================================================================
function createaccessfile(filename:string;password:string=''):boolean;
//建立access文件，如果文件存在則失敗
var
stempfilename:string;
vcatalog:olevariant;
begin
stempfilename:=gettemppathfilename;
try
vcatalog:=createoleobject('adox.catalog');
vcatalog.create(format(sconnectionstring,[stempfilename,password]));
result:=copyfile(pchar(stempfilename),pchar(filename),true);
deletefile(stempfilename);
except
result:=false;
end;
end;
//=============================================================================
// procedure: compactdatabase
// author : ysai
// date : 2003-01-27
// arguments: afilename,apassword:string
// result : boolean
//=============================================================================
function compactdatabase(afilename,apassword:string):boolean;
//壓縮與修復數據庫,覆蓋源文件
var
stempfilename:string;
vje:olevariant;
begin
stempfilename:=gettemppathfilename;
try
vje:=createoleobject('jro.jetengine');
vje.compactdatabase(format(sconnectionstring,[afilename,apassword]),
format(sconnectionstring,[stempfilename,apassword]));
result:=copyfile(pchar(stempfilename),pchar(afilename),false);
deletefile(stempfilename);
except
result:=false;
end;
end;
//=============================================================================
// procedure: changedatabasepassword
// author : ysai
// date : 2003-01-27
// arguments: afilename,aoldpassword,anewpassword:string
// result : boolean
//=============================================================================
function changedatabasepassword(afilename,aoldpassword,anewpassword:string):boolean;
//修改access數據庫密碼
var
stempfilename:string;
vje:olevariant;
begin
stempfilename:=gettemppathfilename;
try
vje:=createoleobject('jro.jetengine');
vje.compactdatabase(format(sconnectionstring,[afilename,aoldpassword]),
format(sconnectionstring,[stempfilename,anewpassword]));
result:=copyfile(pchar(stempfilename),pchar(afilename),false);
deletefile(stempfilename);
except
result:=false;
end;
end;
2.access中使用sql語句應注意的地方及幾點技巧
以下sql語句在access xp的查詢中測試通過
建表:
create table tab1 (
id counter,
name string,
age integer,
[date] datetime);
技巧:
自增字段用 counter 聲明.
字段名為關鍵字的字段用方括號[]括起來,數字作為字段名也可行.
建立索引:
下面的語句在tab1的date列上建立可重復索引
create index idate on tab1 ([date]);
完成后access中字段date索引屬性顯示為 - 有(有重復).
下面的語句在tab1的name列上建立不可重復索引
create unique index iname on tab1 (name);
完成后access中字段name索引屬性顯示為 - 有(無重復).
下面的語句刪除剛才建立的兩個索引
drop index idate on tab1;
drop index iname on tab1;
access與sqlserver中的update語句對比:
sqlserver中更新多表的update語句:
update tab1
set a.name = b.name
from tab1 a,tab2 b
where a.id = b.id;
同樣功能的sql語句在access中應該是
update tab1 a,tab2 b
set a.name = b.name
where a.id = b.id;
即:access中的update語句沒有from子句,所有引用的表都列在update關鍵字后.
上例中如果tab2可以不是一個表,而是一個查詢,例:
update tab1 a,(select id,name from tab2) b
set a.name = b.name
where a.id = b.id;
訪問多個不同的access數據庫-在sql中使用in子句:
select a.*,b.* from tab1 a,tab2 b in 'db2.mdb' where a.id=b.id;
上面的sql語句查詢出當前數據庫中tab1和db2.mdb(當前文件夾中)中tab2以id為關聯的所有記錄.
缺點-外部數據庫不能帶密碼.
補充:看到ugvanxk在一貼中的答復,可以用
select * from [c:/aa/a.mdb;pwd=1111].table1;
access xp測試通過
在access中訪問其它odbc數據源
下例在access中查詢sqlserver中的數據
select * from tab1 in [odbc]
[odbc;driver=sql server;uid=sa;pwd=;server=127.0.0.1;database=demo;]
外部數據源連接屬性的完整參數是:
[odbc;driver=driver;server=server;database=database;uid=user;pwd=password;]
其中的driver=driver可以在注冊表中的
hkey_local_machine/software/odbc/odbcinst.ini/
中找到
異構數據庫之間導數據參見 碧血劍 的
http://www.delphibbs.com/delphibbs/dispq.asp?lid=1691966
access支持子查詢
access支持外連接,但不包括完整外部聯接,如支持
left join 或 right join
但不支持
full outer join 或 full join
access中的日期查詢
注意:access中的日期時間分隔符是#而不是引號
select * from tab1 where [date]>#2002-1-1#;
在delphi中我這樣用
sql.add(format(
'select * from tab1 where [date]>#%s#;',
[datetostr(date)]));
access中的字符串可以用雙引號分隔,但sqlserver不認,所以為了遷移方便和兼容,
建議用單引號作為字符串分隔符.
