Tutorial by Examples: table

You can add an interpreter directive (shebang) to your script. Create a file called hello_world.rb which contains: #!/usr/bin/env ruby puts 'Hello World!' Give the script executable permissions. Here's how to do that in Unix: $ chmod u+x hello_world.rb Now you do not need to call the Ru...

By default, Django renders ForeignKey fields as a <select> input. This can cause pages to be load really slowly if you have thousands or tens of thousand entries in the referenced table. And even if you have only hundreds of entries, it is quite uncomfortable to look for a particular entry amo...

Differences in subsetting syntax A data.table is one of several two-dimensional data structures available in R, besides data.frame, matrix and (2D) array. All of these classes use a very similar but not identical syntax for subsetting, the A[rows, cols] schema. Consider the following data stored i...

LOOP AT itab INTO wa. ENDLOOP. FIELD-SYMBOLS <fs> LIKE LINE OF itab. LOOP AT itab ASSIGNING <fs>. ENDLOOP. LOOP AT itab ASSIGNING FIELD-SYMBOL(<fs>). ENDLOOP. LOOP AT itab REFERENCE INTO dref. ENDLOOP. LOOP AT itab TRANSPORTING NO FIELDS. ENDLOOP. Conditional L...

A view is most useful when it can be used to pull in data from more than one table. CREATE VIEW myview AS SELECT a.*, b.extra_data FROM main_table a LEFT OUTER JOIN other_table b ON a.id = b.id In mysql views are not materialized. If you now perform the simple query SELECT * FROM myview, my...

CREATE TABLE person ( person_id BIGINT NOT NULL, last_name VARCHAR(255) NOT NULL, first_name VARCHAR(255), address VARCHAR(255), city VARCHAR(255), PRIMARY KEY (person_id) ); Alternatively, you can place the PRIMARY KEY constraint directly in the column definition: ...

A metatable defines a set of operations which alter the behaviour of a lua object. A metatable is just an ordinary table, which is used in a special way. local meta = { } -- create a table for use as metatable -- a metatable can change the behaviour of many things -- here we modify the 'tostrin...

Some metamethods don't have to be functions. To most important example for this is the __index metamethod. It can also be a table, which is then used as lookup. This is quite commonly used in the creation of classes in lua. Here, a table (often the metatable itself) is used to hold all the operation...

There is a metamethod called __call, which defines the bevahiour of the object upon being used as a function, e.g. object(). This can be used to create function objects: -- create the metatable with a __call metamethod local meta = { __call = function(self) self.i = self.i + 1 e...

Perhaps the most important use of metatables is the possibility to change the indexing of tables. For this, there are two actions to consider: reading the content and writing the content of the table. Note that both actions are only triggered if the corresponding key is not present in the table. Re...

Sometimes, you don't want to trigger metamethods, but really write or read exactly the given key, without some clever functions wrapped around the access. For this, lua provides you with raw table access methods: -- first, set up a metatable that allows no read/write access local meta = { __i...

The below code will turn the table with an id of tableid into a DataTable, as well as return a DataTables API instance: $(document).ready(function() { $('#tableid').DataTable(); }); Compare this to the below code, which will turn the table into a DataTable but will not return a DataTables ...

Yes, you need to SETKEY pre 1.9.6 In the past (pre 1.9.6), your data.table was sped up by setting columns as keys to the table, particularly for large tables. [See intro vignette page 5 of September 2015 version, where speed of search was 544 times better.] You may find older code making use of t...

A true relational database must go beyond throwing data into a few tables and writing some SQL statements to pull that data out. At best a badly designed table structure will slow the execution of queries and could make it impossible for the database to function as intended. A database table shoul...

Defining our terms By array here we mean a Lua table used as a sequence. For example: -- Create a table to store the types of pets we like. local pets = {"dogs", "cats", "birds"} We're using this table as a sequence: a group of items keyed by integers. Many langua...

Open the psql command line tool connected to the database where your table is. Then type the following command: \d tablename To get extended information type \d+ tablename If you have forgotten the name of the table, just type \d into psql to obtain a list of tables and views in the current ...

Let's say you have a table called person: CREATE TABLE person ( person_id BIGINT NOT NULL, last_name VARCHAR(255) NOT NULL, first_name VARCHAR(255), age INT NOT NULL, PRIMARY KEY (person_id) ); You can create a new table of people over 30 like this: CREATE TABLE p...

DECLARE @Employees TABLE ( EmployeeID INT NOT NULL PRIMARY KEY, FirstName NVARCHAR(50) NOT NULL, LastName NVARCHAR(50) NOT NULL, ManagerID INT NULL ) When you create a normal table, you use CREATE TABLE Name (Columns) syntax. When creating a table variable, you use DECLARE @...

HTML also provides the tables with the <thead>, <tbody>, <tfoot>, and <caption> elements. These additional elements are useful for adding semantic value to your tables and for providing a place for separate CSS styling. When printing out a table that doesn't fit onto one (pa...

For example, if t1 is currently not an InnoDB table, this statement changes its storage engine to InnoDB: ALTER TABLE t1 ENGINE = InnoDB; If the table is already InnoDB, this will rebuild the table and its indexes and have an effect similar to OPTIMIZE TABLE. You may gain some disk space improv...