Tutorial by Examples: del

DELETE FROM `table_name` WHERE `field_one` = 'value_one' This will delete all rows from the table where the contents of the field_one for that row match 'value_one' The WHERE clause works in the same way as a select, so things like >, <, <> or LIKE can be used. Notice: It is necessa...
DELETE FROM table_name ; This will delete everything, all rows from the table. It is the most basic example of the syntax. It also shows that DELETE statements should really be used with extra care as they may empty a table, if the WHERE clause is omitted.
DELETE FROM `table_name` WHERE `field_one` = 'value_one' LIMIT 1 This works in the same way as the 'Delete with Where clause' example, but it will stop the deletion once the limited number of rows have been removed. If you are limiting rows for deletion like this, be aware that it will delete th...
The model is named using the class naming convention of unbroken MixedCase and is always the singular of the table name. For Example: If a table was named orders, the associated model would be named Order For Example: If a table was named posts, the associated model would be named Post Rails will...
Delegates can be used as typed function pointers: class FuncAsParameters { public void Run() { DoSomething(ErrorHandler1); DoSomething(ErrorHandler2); } public bool ErrorHandler1(string message) { Console.WriteLine(message); var shouldWeContinue = ... re...
Deletes all documents matching the query parameter: // New in MongoDB 3.2 db.people.deleteMany({name: 'Tom'}) // All versions db.people.remove({name: 'Tom'}) Or just one // New in MongoDB 3.2 db.people.deleteOne({name: 'Tom'}) // All versions db.people.remove({name: 'Tom'}, true) M...
This query returns all cones with either a mint scoop or a vanilla scoop. minty_vanilla_cones = IceCream.objects.filter(scoops__contained_by=[MINT, VANILLA])
We will model the process #Load the forecast package library(forecast) #Generate an AR1 process of length n (from Cowpertwait & Meltcalfe) # Set up variables set.seed(1234) n <- 1000 x <- matrix(0,1000,1) w <- rnorm(n) # loop to create x for (t in 2:n) x[t] <- 0.7...
Deleting files The unlink function deletes a single file and returns whether the operation was successful. $filename = '/path/to/file.txt'; if (file_exists($filename)) { $success = unlink($filename); if (!$success) { throw new Exception("Cannot delete $filename&qu...
There are a couple of ways to delete a column in a DataFrame. import numpy as np import pandas as pd np.random.seed(0) pd.DataFrame(np.random.randn(5, 6), columns=list('ABCDEF')) print(df) # Output: # A B C D E F # 0 -0.895467 0.386902...
Removing a variable name from the scope using del v, or removing an object from a collection using del v[item] or del[i:j], or removing an attribute using del v.name, or any other way of removing references to an object, does not trigger any destructor calls or any memory being freed in and of itsel...
You can validate any object, even plain ruby. class User include ActiveModel::Validations attr_reader :name, :age def initialize(name, age) @name = name @age = age end validates :name, presence: true validates :age, numericality: { only_integer: true, greater_than...
// MARK: - UICollectionViewDelegateFlowLayout extension ViewController: UICollectionViewDelegateFlowLayout { func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize { return ...
When adding indented code blocks inside a list you first need a blank line, then to indent the code further. Different flavours of Markdown have different rules for this. StackExchange requires code to be indented by 8 characters instead of the usual 4. (Spaces replaced with * for clarity): 1...
XML elements often nest, have data in attributes and/or as character data. The way to capture this data is by using ,attr and ,chardata respectively for those cases. var doc = ` <parent> <child1 attr1="attribute one"/> <child2>and some cdata</child2> </p...
Mage::app()->getStore(); Returns an instance of Mage_Core_Model_Store
Addition + and subtraction - operations can be used to combine delegate instances. The delegate contains a list of the assigned delegates. using System; using System.Reflection; using System.Reflection.Emit; namespace DelegatesExample { class MainClass { private delegate void MyD...
Model using System.ComponentModel.DataAnnotations; public class ViewModel { [Required(ErrorMessage="Name is required")] public string Name { get; set; } [StringLength(14, MinimumLength = 14, ErrorMessage = "Invalid Phone Number")] [Required(ErrorMessag...
Given a JList like JList myList = new JList(items); the selected items in the list can be modified through the ListSelectionModel of the JList: ListSelectionModel sm = myList.getSelectionModel(); sm.clearSelection(); // clears the selection sm.setSelectionInterval(inde...
When you inherit from a class with a property, you can provide a new implementation for one or more of the property getter, setter or deleter functions, by referencing the property object on the parent class: class BaseClass(object): @property def foo(self): return some_calculate...

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