Purpose

This project is based on a really informative and helpful set of blog posts on how to create a SQL parser and execution engine beginning here. Unlike that implementation, this is one is done in Swift and (hopefully properly) takes advantage of the idioms of that language rather than simply being a transliteration of Go code.

Quick start

Use Xcode to open the MyOwnSQL.xcodeproj file. To run the test suite, select the MyOwnSQLTests scheme, click on the ☑️ icon to show the test navigator, then click the ▸ icon on the top right of the navigator. To run the REPL within Xcode and execute queries, select the MyOwnSQL scheme and click the the large ▸ icon. You should see the following in the console:

You may have to adjust the editing settings within Xcode so that hitting backspace works properly within the REPL. Do the following:

• go to the Xcode menu
• select Preferences...
• click the Text Editing tab
• click the Editing tab within that
• uncheck "Enable type-over completions"

Features

This project is still under active development, so the feature set is still in flux. Statements must be delimited by a semicolon character. Keywords can be uppercased or lowercased.

Creating tables

The syntax for creating a new table is the following:

CREATE TABLE table_name (column_definition1, ...);

... where there can be one of more column definitions. Column definitions are of the form:

column_name column_type

As of this time, only INT, TEXT, and BOOLEAN types are supported. Below is an example statement:

CREATE TABLE clothes(id INT, description TEXT, is_fabulous BOOLEAN);

If you enter that into the REPL, it should respond with `Table created.'

It should be noted that currently it is not possible to perform a so-called CTAS (create-table-as-select) statement. Also, there is currently no support for autoincrementing columns that are typically used for primary keys.

Inserting into tables

Records can be inserted into an existing table using the following INSERT statement:

INSERT INTO table_name VALUES (expression1, ...);

... where each expression is a literal value. Below is an example statement:

INSERT INTO clothes VALUES (1, 'Velvet dress', true);

If you enter that into the REPL, and assuming the table above exists, it should respond with `One row inserted.'

Note that at this time, you must insert values for all columns that exist in the table; there is currently no support for nullable columns. Also,it is not possible to insert into a table using a select clause.

Selecting from tables

The syntax for selecting from a table is the following:

SELECT expression1, ... FROM <<table_name>>;

... where each expression is either a literal value or a column with the option to use an AS clause to create an alias for a column. The following is an example statement:

select id, description, is_fabulous from clothes;

If you entered the previous statements, the REPL should look something like this:

| id | description  | is_fabulous |
===================================
| 1  | Velvet dress | true        |

There are a few other limitations at this time:

• no support for WHERE clauses... yet
• no joins are allowed yet; you can only SELECT from one table at a time