sql - problem with Update in MySQL -


According to the document, the update joins with the statement, works just as it is used in selection is. / P>

For example, if we have these two tables: 

  mysql> Choose from the order; + --------- + ------------ + | Ordrid | Customer | + --------- + ------------ + | 1 | 1 | | 2 | 2 | | 3 | 3 | | 4 | 1 | + --------- + ------------ + mysql & gt; Choose from customers; + ------------ + ------------ + | Customer | Order Count | + ------------ + ------------ + | 1 | 9 | | 2 | 3 | | 3 | 8 | | 4 | 5 | | 5 | 7 | By using this select statement:  < Include customers with pre>  Select orders.customerid orders (customers.customerid = orders.customerid)

Returns: 

  + - --- ------- + | Customer | + ------------ + | 1 | | 1 | | 2 | | 3 | So, I was expecting the following statement:  
 Join customers.customerid = orders.customerid) to update order number for customer # 1 (customerid = 1) SET ordercount = ordercount + 1  
 
, but in fact it Not the case, here are the results after the update: 
 
  mysql> Choose from customers; + ------------ + ------------ + | Customer | Order Count | + ------------ + ------------ + | 1 | 10 | | 2 | 4 | | 3 | 9 | | 4 | 5 | | 5 | 7 | + ------------ + ------------ +  
 
 As you can see that only once The order is increased twice in the order table, and despite that, the selected statement correctly. 
 
 Is this a bug in MySQL or is it doing something wrong to me? I am trying to avoid using the group for performance reasons, so my interest is to understand what is happening. 
 
 In advance thanks

Yes, MySQL a record Updates each record as often as possible in the table.

I can not get this document, but practice says.

I will post it as a bug, so they will add it to the minimum document: 

  Table updater (value not INT not NULL); Insert the uper value (1); Select from the uploader; Price --- 1 Update Updater (Select 1 New Union Union Select All 2) q SET u.value = u.value + newval; Select from the uploader; Value --- 2 (required 4)

SQL server , by the way, behaves like one in more than one table UPDATE .

You can use:

update commands SET ordercount = ordercount + (SELECT COUNT (*) customers from C: customerid = o.customerid) < / Code>

is as long as you have an index on customer (customer_id)


Comments

Post a Comment

Popular posts from this blog

python - Overriding the save method in Django ModelForm -

I'm having trouble overriding a ModelForm save method. I get this error I'm: Exception type: TypeErier Exception Value: Save () found an unexpected keyword argument 'committed' My intentions include a form 3 fields Submit several values ​​for, then create an object for each combination of those areas, and to save each object file models.py class collarsult type (models.Model): id = model. AutoField (db_column = 'icontact_result_code_type_id', primary_key = true) callResult = models.ForeignKey ( 'CallResult', db_column = 'icontact_result_code_id') campaign = models.ForeignKey ( 'campaign', db_column = 'icampaign_id') CALLTYPE = models.ForeignKey ( 'CALLTYPE', db_column = 'icall_type_id') agent = models.BooleanField (db_column = 'bagent', default = true) teamLeader = models.BooleanField (db_column = 'bTeamLeader', default = true) active = models.BooleanField (db_column = Django.form...
Read more

html - CSS autoheight, but fit content to height of div -

I have a div in which there are three children- div in the left and middle div: float: left while true: float: true because it is my layout Actually will spoil, I've used ClearFix Hack: .cf {zoom: 1; }. Cf: First,. Cf: {content: ""; Display: Table; }. Cf: After {clear: both; } It still works, but I want to be the right div an indicator. So it should fill 100% of the parent unit of height. How can I complete this? PS is the full code: & Lt; / Div & gt; & Lt; Div class = "mobile_content" & gt; & Lt; H5 & gt; {{Data.titel}} & lt; / H5> & Lt; Table & gt; & Lt; TR & gt; & Lt; Th & gt; Komponist: & lt; / Th & gt; & Lt; TD & gt; {{Data.komponist}} & lt; / TD & gt; & Lt; / TR & gt; & Lt; TR & gt; & Lt; Th & gt; Instrument: & lt; / Th & gt; & Lt; TD & gt; {{Data.instrumente}} & lt; / TD & gt; & Lt; / TR & gt;...
Read more

qt - How to prevent QAudioInput from automatically boosting the master volume to 100%? -

I have been trying to use Qt5 multimedia to record audio with QAudioInput, however, when I see If QAudioInput is started, it increases the master volume of my sound device to 100%. How can I prevent QAudioInput from changing the master volume? My current development platform is Linux with PalsAdio (with flat audio disabled). How can I use QAudioInput : QAudioDeviceInfo device_info = QAudioDeviceInfo :: defaultInputDevice (); QAudio format format; Format.setSampleRate (44100); Format.setChannelCount (1); Format.setSampleSize (16); Format.setCodec ("Audio / PCM"); Format.setSampleType (QAudioFormat :: SignedInt); Format.setByteOrder (QAudioFormat :: LittleEndian); Std :: cout & lt; & Lt; Device_info.deviceName (). ToUtf8 (). ConstData () & lt; & Lt; Std :: endl; QAudioInput * default_device = new QAudioInput (device_info, format); QIODevice * default_io_device = default_device-> Start (); a QAudioInput.setVolume () method is not you I ...
Read more