Write SQL queries in a simple and composable way.

The main goal is to find the best balance between write idiomatic SQL queries and manage scenarios
of complex query composition mixed with conditional clauses.


## Quick Start

```rust
use sql_query_builder as sql;

let mut select = sql::Select::new()
  .select("id, login")
  .from("users")
  .where_clause("login = $1");

let is_admin = true;

if is_admin {
  select = select.where_clause("is_admin = true");
}

let query = select.as_string();

println!("{query}");
```

Output

```sql
SELECT id, login FROM users WHERE login = $1 AND is_admin = true
```


## Feature Flags

SQL Query Builder comes with the following optional features:
- `postgresql` enable Postgres syntax
- `sqlite` enable SQLite syntax

You can enable features like

```toml
# Cargo.toml

sql_query_builder = { version = "2.x.x", features = ["postgresql"] }
```


## How it's works

In a simplified way, the lib has an API to allows you to write dynamic queries in a style
similar to queries written in pure SQL and the result is a code idiomatic to both Rust and SQL.
Additionally, the library will not try to understand what you write in the parameters and in some
ways this is good as it removes a lot of verbosity to generate a SQL query, in contrast,
debugging tends to be more difficult and silly errors can appear, the library has a
[debug()](https://docs.rs/sql_query_builder/latest/sql_query_builder/struct.Select.html#method.debug)
method which had a good output to minimize the effort of debugging complex queries.

More technically, consecutive calls to the same clause will accumulates values respecting the order
of the calls, the two select produce the same SQL query.

```rust
use sql_query_builder as sql;

let select = sql::Select::new()
  .select("id, login");

let select = sql::Select::new()
  .select("id")
  .select("login");
```

Methods like `limit` and `offset` will override the previous value, the two select is equivalent

```rust
# #[cfg(any(feature = "postgresql", feature = "sqlite"))]
# {
use sql_query_builder as sql;

let select = sql::Select::new()
  .limit("1000")
  .limit("123");

let select = sql::Select::new()
  .limit("123");
# }
```

The library ignores the order between clauses so the two selects will produce the same query

```rust
use sql_query_builder as sql;

let select = sql::Select::new()
  .select("id, login")
  .from("users")
  .where_clause("login = $1");

let select = sql::Select::new()
  .from("users")
  .where_clause("login = $1")
  .select("id, login");
```

You can conditionally add a clause mutating the select

```rust
use sql_query_builder as sql;

let mut select = sql::Select::new()
  .select("id, login")
  .from("users")
  .where_clause("login = $1");

let should_includes_address = true;

if should_includes_address {
  select = select.inner_join("addresses on user.login = addresses.owner_login");
}
```


## Composition

Composition is very welcome to write complex queries, this feature makes the library shine

```rust
use sql_query_builder as sql;

fn project(select: sql::Select) -> sql::Select {
  select
    .select("u.id, u.name as user_name, u.login")
    .select("a.name as addresses_name")
    .select("o.name as product_name")
}

fn relations(select: sql::Select) -> sql::Select {
  select
    .from("users u")
    .inner_join("addresses a ON a.user_login = u.login")
    .inner_join("orders o ON o.user_login = u.login")
}

fn conditions(select: sql::Select) -> sql::Select {
  select
    .where_clause("u.login = $1")
    .where_clause("o.id = $2")
}

fn as_string(select: sql::Select) -> String {
  select.as_string()
}

let query = Some(sql::Select::new())
  .map(project)
  .map(relations)
  .map(conditions)
  .map(as_string)
  .unwrap();

println!("{query}");
```

Output (indented for readability)

```sql
SELECT u.id, u.name as user_name, u.login, a.name as addresses_name, o.name as product_name
FROM users u
INNER JOIN addresses a ON a.user_login = u.login
INNER JOIN orders o ON o.user_login = u.login
WHERE u.login = $1 AND o.id = $2
```


## Raw queries

You can use the raw method to reach some edge cases that are hard to rewrite into the Select syntax.
The `select.raw()` method will put any SQL you define on top of the output

```rust
use sql_query_builder as sql;

let raw_query = "\
  select u.id as user_id, addr.* \
  from users u \
  inner join addresses addr on u.login = addr.owner_login\
";
let select = sql::Select::new()
  .raw(raw_query)
  .where_clause("login = $1");
```

To a more precisely use case your can use the `select.raw_before()` and `select.raw_after()`

```rust
use sql_query_builder as sql;

let raw_query = "\
  from users u \
  inner join addresses addr on u.login = addr.owner_login\
";
let select = sql::Select::new()
  .select("u.id as user_id, addr.*")
  .raw_before(sql::SelectClause::Where, raw_query)
  .where_clause("login = $1");
```

```rust
use sql_query_builder as sql;

let raw_query = "\
  from users u \
  inner join addresses addr on u.login = addr.owner_login\
";
let select = sql::Select::new()
  .select("u.id as user_id, addr.*")
  .raw_after(sql::SelectClause::Select, raw_query)
  .where_clause("login = $1");
```

## Debugging queries

Sometimes it's more ease just print de current state of the query builder, to do so adds the `.debug()` method anywhere in the builder.
In the example below, the where clause will not be printed because the debug was added before the clause

```rust
use sql_query_builder as sql;

let mut select = sql::Select::new()
  .select("id, login")
  .from("users")
  .debug()
  .where_clause("login = $1");
```

Prints to the standard output

```sql
-- ------------------------------------------------------------------------------
SELECT id, login
FROM users
-- ------------------------------------------------------------------------------
```

See the [documentation](https://docs.rs/sql_query_builder/) for more builders like [Insert](https://docs.rs/sql_query_builder/latest/sql_query_builder/struct.Insert.html), [Update](https://docs.rs/sql_query_builder/latest/sql_query_builder/struct.Update.html) and [Delete](https://docs.rs/sql_query_builder/latest/sql_query_builder/struct.Delete.html)