sql查询语句的拼接小技巧（高手勿喷）

1. 基本的查询语句后面加上 WHERE 1=1，便于增加查询条件。

ASkStr := \'select * from Twork where 1=1 \';
if length(cxTEworkid.Text) <> 0 then 
begin
ASkStr := ASkStr + \' and GWORKID like \' +
quotedstr(\'%\' + cxTEworkid.Text + \'%\')
end;

　　

2. 多表查询可以用一个字符串代替一个表。逻辑上更清晰。

  

WorkTable = \'select GWorkId from TWork where 1=1 \';
PayTable = \'select sum(GXMtotal) as SGXMtotal,GXMType from TPAY where GWorkId In \';
PayGroupBy = \' Group By GXMType \';

ASkStr := PayTable + \' ( \' + WorkTable + tmpwhere + \' ) \' + PayGroupBy;

 

3.自己定义一个连接函数，判断数据库初始化是否成功，便于控制。

  

function Tdm.InitDbOk: boolean;
begin
  result := true;
  if fileexists(DBFileName) then
  begin
    FDConn.DriverName := \'SQLite\';
    FDConn.LoginPrompt := false;
    FDConn.Params.Clear;
    FDConn.Params.Values[\'Database\'] := DBFileName;
    FDConn.Params.Values[\'DriverID\'] := \'SQLite\';
    FDConn.Params.Values[\'CharacterSet\'] := \'utf8\';
    try
      FDConn.Connected := true;
    except
      result := false;
    end;
  end
  else
    result := false;
end;