CQL by example

This web page will discuss in some detail the examples listed in the sidebar under the heading Examples. They should be read in order.

Setting up

Unfortunately, CQL does not have a one-click installation. In fact, installing and getting set up to use CQL is probably the trickiest part of CQL for many chess players.

1. Download and install CQL
2. If you on Windows and using VisualCQL, install that.
3. Make sure that the file sample database is in the directory where you are going to run the examples from. Or, if you want to run the examples on, say, the HHdbVI endgame study database, make sure that the hhdbvi.pgn file is in that directory.

All of the examples are in the distributed versio of cql in the examples/ subdirectory of the main distribution. You can also access the examples online. However, if you access the examples online, you will have to download the ones you use individually - the CQL program cannot read .cql files from a URL but requires the name of a local file.

Running the examples

The examples themselves by default use the hhdbvi.pgn database to search for games from. This what the input hhdbvi.pgn means at the start of the examples.

But if you do not have this database, you should use sample.pgn instead. There are two ways to use sample.pgn:

• change hhdbvi.pgn to sample.pgn in the examples you want to run, or
• run CQL with the -i sample.pgn option:

  cql -i sample.pgn examples/turton.cql

  This will generate a file in the current directory named turton-out.pgn which you view with any PGN viewer, like ChessBase or HiArcs or the built-in chess viewer in VisualCQL.

Example explanations

The explanations of the examples discussed:

CQL file	Theme	filters discussed
QQqq	QQ v. qq	piece designators ♕♛ ==
loneknightmate	mate with knight	♘△ mate
greekgift	Greek gift	⊢ ―― ×
smotheredmate	smothered mate	□ → not btm mate
mirrormate	mirror mate	⬓ ← filter values
rookleapcorners	♖ visits 4 corners in 3 moves	square variables ∊ ✵ ◎ focus
staircase-sort-annotated	queen staircase	sort up right piecepath regular expressions in ⊢
likeinterference	interference theme	piece variables ◭ ∪ → → chaining
turton	Turton theme	piece variables ∩ ∪ from → → chaining
dingstheme	Ding's theme	modelmate ▦ King's field