sqlite - 带条件的 SQLITE 多表连接

Question

我有这些表：

多迪亚

dhid INTEGER PRIMARY KEY NOT NULL, 
dname TEXT NOT NULL, 
dfname TEXT NOT NULL, 
dage INTEGER NOT NULL, 
dadd TEXT, 
dphone INTEGER NOT NULL, 
demail TEXT NOT NULL

数据

dtid INTEGER PRIMARY KEY NOT NULL, 
ddate INTEGER NOT NULL, 
dmonth INTEGER NOT NULL,
dyear INTEGER NOT NULL, 
dmilk INTEGER NOT NULL, 
dprice INTEGER NOT NULL default 35 , 
dmore TEXT, 
ddhid INTEGER NOT NULL

价格牛奶

pid INTEGER PRIMARY KEY NOT NULL, 
pmonth INTEGER NOT NULL, 
pyear INTEGER NOT NULL, 
milkprice INTEGER NOT NULL, 
typeperson TEXT, 
userid INTEGER, 
gheeprice INTEGER, 
defaultprice TEXT

现金数据

cashid INTEGER PRIMARY KEY NOT NULL,
cashdate INTEGER NOT NULL, 
cashmonth INTEGER NOT NULL, 
cashyear INTEGER NOT NULL, 
cashamount INTEGER NOT NULL, 
uid INTEGER NOT NULL, 
utype TEXT NOT NULL, 
cashtype TEXT NOT NULL, 
cashmore TEXT

我想制作每月账单，我成功使用它购买了......但是在账单中我如何显示上个月的余额......我正在尝试使用它

 SELECT
  ddhid, dmonth, dyear, dmilk,
  userid, pmonth, pyear, milkprice, 
  uid, cashmonth, cashyear, cashamount, utype, 
  SUM(dmilk) AS totalmilk,  
  SUM(dmilk*milkprice) AS totalamount, 
  SUM(cashamount) AS totalcash
  FROM 
 doodhdata 
 LEFT JOIN pricemilk ON (
   doodhdata.ddhid = pricemilk.userid 
   AND doodhdata.dmonth = pricemilk.pmonth 
   AND doodhdata.dyear = pricemilk.pyear
 )
 LEFT JOIN cashdata ON (
   doodhdata.ddhid = cashdata.uid 
   AND doodhdata.dmonth = cashdata.cashmonth 
   AND doodhdata.dyear = cashdata.cashyear
 )
 WHERE 
   dmonth > '$mikdatem' 
   AND dyear='$mikdatey' 
   AND ddhid='$dhid'

但是我想在 milkprice 为 NULL 时使用 defaultprice ......怎么可能......？

Answer 1

利用

COALESCE(milkprice, defaultprice)

代替milkprice您的查询。

请参阅SQLite 核心函数文档。