Types of joins in SQL (cheatsheet for beginners)

Submitted by st on Wed, 05/10/2016 - 14:26

This article is used in my book "Programming with databases".

Better to see once than to hear a hundred times. This small article explains what are the different kinds of joins in SQL.

At the first time you should take into account that SQL is a declarative 4th generation language. So the best way to use it (especially for beginners) is to write the query and let SQL optimizer do its job. That means thinking in set-oriented terms and avoiding sub-queries.

Let's take two example tables: Companies and Contacts.

Programming

Using Delphi library with C++ Builder

Submitted by st on Thu, 29/09/2016 - 12:23

Since early XE versions C++ Builder supports Delphi units directly added in C++ project and compiles them as well as C/C++ source. However, this approach has several drawbacks:

Programming

C++ |
C++Builder

SQL: generate list (sequence) of integer values

Submitted by st on Thu, 22/09/2016 - 15:19

Here are some examples of SQL to generate a sequence of numeric (integer) values from 0 to 99.

Programming

SQL |
SQL Server

Delphi Starter doesn't support command line

Submitted by st on Tue, 09/08/2016 - 12:28

Delphi feature matrix has two important points:

Delphi 32-bit native code optimizing compiler (dcc32) for Windows, including high performance x86
Assembler
Delphi toolchains for Windows

Regardless indicated options dcc32 doesn't work in Delphi Berlin Starter with the error message "This version of the product does not support command line compiling".

Delphi attributes and ordinal (simple) types

Submitted by st on Tue, 24/05/2016 - 16:28

The custom attributes don't work with ordinal (simple) type aliases in Delphi including last version XE 10.

Delphi

Happy tickets benchmark

Submitted by st on Sat, 13/02/2016 - 10:49

Some countries have integer numbers printed on the transport tickets, for example, in ex-USSR. The ticket is "happy" when the sum of the first half of digits equals to the second one. Then you should eat it and make a wish.

Example:

123456 and 111222 are not happy tickets
123123 and 123222 are the happy tickets

Testing

Installing Delphi 7 on Windows 7/8/10/Server 2012

Submitted by st on Tue, 19/01/2016 - 10:36

How to install and use Delphi 7 and help files on Windows 8/10 or Server 2012.

Delphi

Bit-packed structure (record) in Free Pascal and Delphi

Submitted by st on Sat, 19/12/2015 - 11:58

Here is the code explaining some methods to pack bit accessing logic in your program.

program project1;
 
type
  TRec1 = packed record // Doesn't pack at all
    b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15, b16: boolean;
  end;
 
  TRec2 = bitpacked record // Free Pascal specific
    b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15, b16: boolean;
  end;
 
  TRecByte = (b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15, b16);
  TRecBytes = set of TRecByte;
var
  r1: TRec1;
  r2: TRec2;
  s1: TRecBytes;

Programming

Delphi |
Free Pascal

Precise optimisation of Transact SQL queries

Submitted by st on Sat, 28/11/2015 - 14:44

As DBAs know, Database Tuning Advisor can help you in some cases.

Testing

SQL Server

Windows XP multiprocessor/core support

Submitted by st on Tue, 25/08/2015 - 09:31

How to add support of multi-core/multiprocessor support to Windows XP SP3?

Run this in command line:

rundll32 syssetup,SetupInfObjectInstallAction ACPIAPIC_MP_HAL 128 %windir%\inf\hal.inf

This command replace single-core kernel to multi-core kernel without reinstalling Windows. You should be required to confirm driver installation and to reboot twice.

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