sql - Detecting the change on the certain column in the history table -


consider following data:

history.data ======================================= id |data_id| col1  | col2  | date ---+-------+-------+-------+----------- 1  |1      | 123   | 321   | 2017-08-01 2  |1      | 124   | 321   | 2017-08-03 3  |2      | 222   | 555   | 2017-08-05 4  |2      | 242   | 555   | 2017-08-07 5  |2      | 242   | 333   | 2017-08-11

so history_data table keep changes in table. right need date of last change every present entry of data in col1 column. in case desired output should be

data_id | date --------+----------- 1       | 2017-08-03 2       | 2017-08-07

i need in following context:

with cte1 (     select distinct on(data_id)     data_id,     date::date      data d     join history.data hd on hd.data_id = d.id     order d.id, hd.date desc )

so can see, i'm getting date of last record change, regardless of on column change occured.

could please me that?

you can use lag() previous prev_col1 value , prev_col1 <> col1 identify rows change occured:

select distinct on(data_id) * (     select lag(col1) on (partition data_id order d.id) prev_col1,     d.id,     col1,     data_id,     date::date     data d     join history.data hd on hd.data_id = d.id ) t prev_col1 <> col1 or prev_col1 null order id desc

the prev_col1 null condition needed groups 1 member per data_id , assumes first member qualifies change.


Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more