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SELECT size FROM modules WHERE name = 'clock';
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SQL beginners' guide
Руководство для начинающих по SQL
The Beginners' Guide describes how users can start up with SQL with Tarantool, and necessary concepts.
В этом руководстве описано, как пользователю начать работу с SQL в Tarantool, а также объясняются все необходимые понятия.
The SQL Beginners' Guide is about databases in general, and about the relationship between Tarantool's NoSQL and SQL products. Most of the matters in the Beginners' Guide will already be familiar to people who have used relational databases before.
Ниже рассказывается о базах данных в целом и взаимосвязи между решениями NoSQL и SQL в Tarantool. Большинство тем, изложенных в этом руководстве, будут знакомы тем, кто уже использовал реляционные базы данных.
Sample table
**Пример простой таблицы**
In football training camp it is traditional for the trainer to begin by showing a football and saying "this is a football". In that spirit, this is a table:
В футбольном тренировочном лагере тренер традиционно начинает с того, что показывает игрокам футбольный мяч и говорит: "Это --- футбольный мяч". В случае SQL подобный базовый объект --- это таблица:
TABLE
[1] [2] [3]
+-----------------+----------------+----------------+
Row#1 | Row#1,Column#1 | Row#1,Column#2 | Row#1,Column#3 |
+-----------------+----------------+----------------+
Row#2 | Row#2,Column#1 | Row#2,Column#2 | Row#2,Column#3 |
+-----------------+----------------+----------------+
Row#3 | Row#3,Column#1 | Row#3,Column#2 | Row#3,Column#3 |
+-----------------+----------------+----------------+
TABLE
[1] [2] [3]
+-----------------+----------------+----------------+
Стрк1 | Стрк1, Стлб1 | Стрк1, Стлб2 | Стрк1, Стлб3 |
+-----------------+----------------+----------------+
Стрк2 | Стрк2, Стлб1 | Стрк2, Стлб2 | Стрк2, Стлб3 |
+-----------------+----------------+----------------+
Стрк3 | Стрк3, Стлб1 | Стрк3, Стлб2 | Стрк3, Стлб3 |
+-----------------+----------------+----------------+
But the labels are misleading -- one usually doesn't identify rows and columns by their ordinal positions, one prefers to pick out specific items by their contents. In that spirit, this is a table:
Но эти обозначения вводят в заблуждение. Обычно мы не обозначаем строки и столбцы порядковыми позициями, мы скорее будем искать элементы таблицы по их содержимому:
MODULES

+-----------------+------+---------------------+
| NAME | SIZE | PURPOSE |
+-----------------+------+---------------------+
| box | 1432 | Database Management |
| clock | 188 | Seconds |
| crypto | 4 | Cryptography |
+-----------------+------+---------------------+
MODULES

+-----------------+------+---------------------+
| NAME | SIZE | PURPOSE |
+-----------------+------+---------------------+
| box | 1432 | Управление БД |
| clock | 188 | Секунды |
| crypto | 4 | Криптография |
+-----------------+------+---------------------+
So one does not use longitude/latitude navigation by talking about "Row#2 Column #2", one uses the contents of the Name column and the name of the Size column by talking about "the size, where the name is 'clock'". To be more exact, this is what one says:
Так что мы не используем навигацию по позиции, обращаясь к элементу "Строка #2, столбец #2"; мы используем содержимое колонок "name" (имя) и "size" (размер), и ищем значение "size" для элемента, для которого значение "name" совпадает с 'clock'. Если быть точнее, вот что мы говорим:
SELECT size FROM modules WHERE name = 'clock';
``SELECT size FROM modules WHERE name = 'clock';``
If you're familiar with Tarantool's architecture -- and ideally you read about that before coming to this chapter -- then you know that there is a NoSQL way to get the same thing:
 
box.space.MODULES:select()[2][2]
 
Well, you can do that. One of the advantages of Tarantool is that if you can get data via an SQL statement, then you can get the same data via a NoSQL request. But the reverse is not true, because not all NoSQL tuple sets are definable as SQL tables. These restrictions apply for SQL that do not apply for NoSQL: |br| 1. Every column must have a name. |br| 2. Every column should have a scalar type (Tarantool is relaxed about which particular scalar type you can have, but there is no way to index and search arrays, tables within tables, or what MessagePack calls "maps".)
 
Tarantool/NoSQL's "format" clause causes the same restrictions.
 
So an SQL "table" is a NoSQL "tuple set with format restrictions", an SQL "row" is a NoSQL "tuple", an SQL "column" is a NoSQL "list of fields within a tuple set".
 
Creating a table
**Создание таблицы**
This is how to create the modules table:
 
CREATE TABLE modules (name STRING, size INTEGER, purpose STRING, PRIMARY KEY (name));
 
The words that are IN CAPITAL LETTERS are "keywords" (although it is only a convention in this manual that keywords are in capital letters, in practice many programmers prefer to avoid shouting). A keyword has meaning for the SQL parser so many keywords are reserved, they cannot be used as names unless they are enclosed inside quotation marks.
 
The word "modules" is a "table name", and the words "name" and "size" and "purpose" are "column names". All tables and all columns must have names.
 
The words "STRING" and "INTEGER" are "data types". STRING means "the contents should be characters, the length is indefinite, the equivalent NoSQL type is 'string''". INTEGER means "the contents should be numbers without decimal points, the equivalent NoSQL type is 'integer'". Tarantool supports other data types but this section's example table has data types from the two main groups, namely, data types for numbers and data types for strings.
 
The final clause, PRIMARY KEY (name), means that the name column is the main column used to identify the row.
 
Nulls
 
Frequently it is necessary, at least temporarily, that a column value should be NULL. Typical situations are: the value is unknown, or the value is not applicable. For example, you might make a module as a placeholder but you don't want to say its size or purpose. If such things are possible, the column is "nullable". The example table's name column cannot contain nulls, and it could be defined explicitly as "name STRING NOT NULL", but in this case that's unnecessary -- a column defined as PRIMARY KEY is automatically NOT NULL.
 
Is a NULL in SQL the same thing as a nil in Lua? No, but it is close enough that there will be confusion. When nil means "unknown" or "inapplicable", yes. But when nil means "nonexistent" or "type is nil", no. NULL is a value, it has a data type because it is inside a column which is defined with that data type.
 

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testing_project / Documentation: how-to/sql/sql_beginners_guide — Russian

SELECT size FROM modules WHERE name = 'clock';
``SELECT size FROM modules WHERE name = 'clock';``
a year ago
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locale/ru/LC_MESSAGES/how-to/sql/sql_beginners_guide.po, string 10