README

This library does not generate any SQL, instead it provides an object oriented representation of SQL queries, allowing the structure of queries to be defined by the developer whilst gaining the benefits of inheritance.

When a PHP application reaches scale, it is often the database that is the performance bottleneck. When queries are generated on behalf of the developer, they are often difficult to optimise because control is lost. With SqlBuilder, the developer is always in control of the raw SQL.

Example usage: a class that represents a SELECT query

Imagine a typical database application with a student table used to store details of each student. A basic select might look something like this:

select
	id,
	forename,
	surname,
	dateOfBirth
from
	student

The above query will return a list of all students. The problem here is that when you come to need to select from the student table again, this time with some constraints such as an age range or ordered by surname, the whole query will need to be repeated and only a small portion of the original query will need to be changed.

Instead, the following class can be used to represent the above query:

class StudentSelect extends SelectQuery {
	public function select():array {
		return [
			"id",
			"forename",
			"surname",
			"dateOfBirth",
		];
	}
	
	public function from():array {
		return [
			"student",
		];
	}
}

The __toString method of the above class will produce identical SQL to the original query.

Now, to write another query that returns students of a certain age:

class StudentSelectByAge extends StudentSelect {
	public function where():array {
		return [
			"year(now()) - year(dateOfBirth) = :age",
		];
	}
}

Example usage: A fluent class that builds a SELECT query (coming in v2 release)

As you can see in the example above, SqlQuery functions always return an array of expressions. The SqlBuilder classes have the same methods (select, from, where, etc.) but take the expressions as parameters, acting as a fluent interface.

To create the same query as in the example above with fluent syntax:

$selectQuery = new SelectBuilder(
	"id",
	"forename",
	"surname",
	"dateOfBirth"
)->from(
	"student"
)->where(
	"year(now()) - year(dateOfBirth) = :age"
);

This is particularly useful for when there is a base query, say StudentSelect, and your code only requires a single additional condition. Rather than having to create a separate class for this single usage, it can be called inline:

// Start by using a base StudentSelect, then add a single inline condition to it.
$studentSelect = new StudentSelect();

$selectQuery = new SelectBuilder($studentSelect)
->where(
	"year(now()) - year(dateOfBirth) = :age"
);

Conditionals

Expressions within where and having clauses can be connected with logical operators, which are often combined. To avoid logical errors, Condition objects are used to specify the precedence of logic.

For example, to select students with a specific age and gender:

class StudentSelectByAge extends StudentSelect {
	public function where():array {
		return [
			new AndCondition("year(now()) - year(dateOfBirth) = :age"),
			new AndCondition("gender = :gender"),
		];
	}
}

Subqueries

SqlQuery objects have a __toString() function, and SqlBuilder results create SqlQuery instances. Because of this, they can be used in place of any other expression within a Query or Builder.

Limitations of plain SQL

The only tools provided by plain SQL that can be used to write DRY code are views and stored procedures, both of which have their own set of limitations when writing clean and maintainable code.

The solution provided by this library is to break down an SQL query into its different sections, represented by a PHP class which can be extended by other classes, while still retaining the plain SQL that is being represented.

SQL compatibility

This library does not provide any SQL processing capabilities by design. Any driver-specific SQL used will not be compatible with other drivers. This allows the developer to fully utilise their SQL driver of choice, rather than generating generic SQL.