Tutorial by Examples: column

Consider a database with the following two tables. Employees table: IdFNameLNameDeptId1JamesSmith32JohnJohnson4 Departments table: IdName1Sales2Marketing3Finance4IT Simple select statement * is the wildcard character used to select all available columns in a table. When used as a substitute f...

SELECT PhoneNumber, Email, PreferredContact FROM Customers This statement will return the columns PhoneNumber, Email, and PreferredContact from all rows of the Customers table. Also the columns will be returned in the sequence in which they appear in the SELECT clause. The re...

ALTER TABLE Employees ADD StartingDate date NOT NULL DEFAULT GetDate(), DateOfBirth date NULL The above statement would add columns named StartingDate which cannot be NULL with default value as current date and DateOfBirth which can be NULL in Employees table.

Column aliases are used mainly to shorten code and make column names more readable. Code becomes shorter as long table names and unnecessary identification of columns (e.g., there may be 2 IDs in the table, but only one is used in the statement) can be avoided. Along with table aliases this allows ...

A simple two-column layout consists of two fixed-width, floated elements. Note that the sidebar and content area are not the same height in this example. This is one of the tricky parts with multi-column layouts using floats, and requires workarounds to make multiple columns appear to be the same he...

HTML: <div class="wrapper"> <div class="left-sidebar"> <h1>Left Sidebar</h1> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. </p> </div> <div class="content"> <h1>Content</h1&g...

This layout uses one floated column to create a two-column layout with no defined widths. In this example the left sidebar is "lazy," in that it only takes up as much space as it needs. Another way to say this is that the left sidebar is "shrink-wrapped." The right content column...

INSERT INTO Customers (FName, LName, Email, PreferredContact) VALUES ('Zack', 'Smith', '[email protected]', 'EMAIL'); This statement will insert a new row into the Customers table. Data will only be inserted into the columns specified - note that no value was provided for the PhoneNumber column. ...

Use Case CASE can be used in conjunction with SUM to return a count of only those items matching a pre-defined condition. (This is similar to COUNTIF in Excel.) The trick is to return binary results indicating matches, so the "1"s returned for matching entries can be summed for a count o...

Using Item Sales Table from Example Database, let us calculate and show the total Quantity we sold of each Product. This can be easily done with a group by, but lets assume we to 'rotate' our result table in a way that for each Product Id we have a column. SELECT [100], [145] FROM (SELECT ItemI...

In this example, we can use GROUP BY not only determined the sort of the rows returned, but also what rows are returned, since we're using TOP to limit the result set. Let's say we want to return the top 5 highest reputation users from an unnamed popular Q&A site. Without ORDER BY This query ...

Let's say you want to generate counts or subtotals for a given value in a column. Given this table, "Westerosians": NameGreatHouseAllegienceAryaStarkCerceiLannisterMyrcellaLannisterYaraGreyjoyCatelynStarkSansaStark Without GROUP BY, COUNT will simply return a total number of rows: SELE...

Syntax for accessing rows and columns: [, [[, and $ This topic covers the most common syntax to access specific rows and columns of a data frame. These are Like a matrix with single brackets data[rows, columns] Using row and column numbers Using column (and row) names Like a list: Wi...

SELECT DisplayName, JoinDate, Reputation FROM Users ORDER BY JoinDate, Reputation DisplayNameJoinDateReputationCommunity2008-09-151Jeff Atwood2008-09-1625784Joel Spolsky2008-09-1637628Jarrod Dixon2008-10-0311739Geoff Dalgas2008-10-0312567

Syntax: SELECT * FROM table_name Using the asterisk operator * serves as a shortcut for selecting all the columns in the table. All rows will also be selected because this SELECT statement does not have a WHERE clause, to specify any filtering criteria. This would also work the same way if you...

Table cells can span multiple columns or rows using the colspan and rowspan attributes. These attributes can be applied to <th> and <td> elements. <table> <tr> <td>row 1 col 1</td> <td>row 1 col 2</td> <td>row 1 c...

ALTER TABLE Employees DROP COLUMN salary; This will not only delete information from that column, but will drop the column salary from table employees(the column will no more exist).

In this example, we will look at a method for returning the last non-empty row in a column for a data set. This method will work regardless of empty regions within the data set. However caution should be used if merged cells are involved, as the End method will be "stopped" against a mer...

You can use a column's number (where the leftmost column is '1') to indicate which column to base the sort on, instead of describing the column by its name. Pro: If you think it's likely you might change column names later, doing so won't break this code. Con: This will generally reduce readabilit...

To add a new column name to the users table, run the command: rails generate migration AddNameToUsers name This generates the following migration: class AddNameToUsers < ActiveRecord::Migration[5.0] def change add_column :users, :name, :string end end When the migration name i...