# SQLBuilder

Contents

- SQLBuilder
  - SQLExpression
  - SQL statements
    - Select
    - Insert
    - Update
    - Delete
    - Union
  - Nested SQL statements (subqueries)

A number of variables from SQLBuilder are included with `from sqlobject import *` – see the relevant SQLObject documentation for more. Its functionality is also available through the special `q` attribute of SQLObject classes.

## SQLExpression

SQLExpression uses clever overriding of operators to make Python expressions build SQL expressions – so long as you start with a Magic Object that knows how to fake it.

With SQLObject, you get a Magic Object by accessing the `q` attribute of a table class – this gives you an object that represents the field. All of this is probably easier to grasp in an example:

    >>> from sqlobject.sqlbuilder import *
    >>> person = table.person
    # person is now equivalent to the Person.q object from the SQLObject
    # documentation
    >>> person
    person
    >>> person.first_name
    person.first_name
    >>> person.first_name == 'John'
    person.first_name = 'John'
    >>> name = 'John'
    >>> person.first_name != name
    person.first_name != 'John'
    >>> AND(person.first_name == 'John', person.last_name == 'Doe')
    (person.first_name = 'John' AND person.last_name = 'Doe')

Most of the operators work properly: <, >, <=, >=, !=, ==, +, -, /, *, **, %. However, `and`, `or`, and `not` do not work. You can use &, |, and ~ instead – but be aware that these have the same precedence as multiplication. So:

    # This isn't what you want:
    >> person.first_name == 'John' & person.last_name == 'Doe'
    (person.first_name = ('John' AND person.last_name)) = 'Doe')
    # This is:
    >> (person.first_name == 'John') & (person.last_name == 'Doe')
    ((person.first_name = 'John') AND (person.last_name == 'Doe'))

SQLBuilder also contains the functions `AND`, `OR`, and `NOT` which also work – I find these easier to work with. `AND` and `OR` can take any number of arguments.

You can also use `.startswith()` and `.endswith()` on an SQL expression – these will translate to appropriate `LIKE` statements and all `%` quoting is handled for you, so you can ignore that implementation detail. There is also a `LIKE` function, where you can pass your string, with `%` for the wildcard, as usual.

If you want to access an SQL function, use the `func` variable, like:

    >> person.created < func.NOW()

To pass a constant, use the `const` variable which is actually an alias for func.

## SQL statements

SQLBuilder implements objects that execute SQL statements. SQLObject uses them internally in its higher-level API, but users can use this mid-level API to execute SQL queries that are not supported by the high-level API. To use these objects first construct an instance of a statement object, then ask the connection to convert the instance to an SQL query and finally ask the connection to execute the query and return the results. For example, for `Select` class:

    >>> from sqlobject.sqlbuilder import *
    >> select = Select(['name', 'AVG(salary)'], staticTables=['employees'],
    >>     groupBy='name') # create an instance
    >> query = connection.sqlrepr(select) # Convert to SQL string:
    >>     # SELECT name, AVG(salary) FROM employees GROUP BY name
    >> rows = connection.queryAll(query) # Execute the query
    >>     # and get back the results as a list of rows
    >>     # where every row is a sequence of length 2 (name and average salary)

### Select

A class to build `SELECT` queries. Accepts a number of parameters, all parameters except items are optional. Use `connection.queryAll(query)` to execute the query and get back the results as a list of rows.

items:
  A string, an SQLExpression or a sequence of strings or SQLExpression’s, represents the list of columns. If there are q-values SQLExpression’s `Select` derives a list of tables for SELECT query.
where:
  A string or an SQLExpression, represents the `WHERE` clause.
groupBy:
  A string or an SQLExpression, represents the `GROUP BY` clause.
having:
  A string or an SQLExpression, represents the `HAVING` part of the `GROUP BY` clause.
orderBy:
  A string or an SQLExpression, represents the `ORDER BY` clause.
join:
  A (list of) JOINs (`LEFT JOIN`, etc.)
distinct:
  A bool flag to turn on `DISTINCT` query.
start, end:
  Integers. The way to calculate `OFFSET` and `LIMIT`.
limit:
  An integer. limit, if passed, overrides end.
reversed:
  A bool flag to do `ORDER BY` in the reverse direction.
forUpdate:
  A bool flag to turn on `SELECT FOR UPDATE` query.
staticTables:
  A sequence of strings or SQLExpression’s that name tables for `FROM`. This parameter must be used if items is a list of strings from which Select cannot derive the list of tables.

### Insert

A class to build `INSERT` queries. Accepts a number of parameters. Use `connection.query(query)` to execute the query.

table:
  A string that names the table to `INSERT` into. Required.
valueList:

  A list of (key, value) sequences or {key: value} dictionaries; keys are column names. Either valueList or values must be passed, but not both. Example:

      >> insert = Insert('person', valueList=[('name', 'Test'), ('age', 42)])
             # or
      >> insert = Insert('person', valueList=[{'name': 'Test'}, {'age': 42}])
      >> query = connection.sqlrepr(insert)
             # Both generate the same query:
             # INSERT INTO person (name, age) VALUES ('Test', 42)
      >> connection.query(query)

values:

  A dictionary {key: value}; keys are column names. Either valueList or values must be passed, but not both. Example:

      >> insert = Insert('person', values={'name': 'Test', 'age': 42})
      >> query = connection.sqlrepr(insert)
             # The query is the same
             # INSERT INTO person (name, age) VALUES ('Test', 42)
      >> connection.query(query)

Instances of the class work fast and thus are suitable for mass-insertion. If one needs to populate a database with SQLObject running a lot of `INSERT` queries this class is the way to go.

### Update

A class to build `UPDATE` queries. Accepts a number of parameters. Use `connection.query(query)` to execute the query.

table:
  A string that names the table to `UPDATE`. Required.
values:
  A dictionary {key: value}; keys are column names. Required.
where:
  An optional string or SQLExpression, represents the `WHERE` clause.

Example:

    >> update = Update('person',
    >>     values={'name': 'Test', 'age': 42}, where='id=1')
    >> query = connection.sqlrepr(update)
           # UPDATE person SET name='Test', age=42 WHERE id=1
    >> connection.query(query)

### Delete

A class to build `DELETE FROM` queries. Accepts a number of parameters. Use `connection.query(query)` to execute the query.

table:
  A string that names the table to `UPDATE`. Required.
where:
  An optional string or an SQLExpression, represents the `WHERE` clause. Required. If you need to delete all rows pass `where=None`; this is a safety measure.

Example:

    >> update = Delete('person', where='id=1')
    >> query = connection.sqlrepr(update)
           # DELETE FROM person WHERE id=1
    >> connection.query(query)

### Union

A class to build `UNION` queries. Accepts a number of parameters - `Select` queries. Use `connection.queryAll(query)` to execute the query and get back the results.

Example:

    >> select1 = Select(['min', func.MIN(const.salary)], staticTables=['employees'])
    >> select2 = Select(['max', func.MAX(const.salary)], staticTables=['employees'])
    >> union = Union(select1, select2)
    >> query = connection.sqlrepr(union)
           # SELECT 'min', MIN(salary) FROM employees
           #    UNION
           # SELECT 'max', MAX(salary) FROM employees
    >> rows = connection.queryAll(query)

## Nested SQL statements (subqueries)

There are a few special operators that receive as parameter SQL statements. These are `IN`, `NOTIN`, `EXISTS`, `NOTEXISTS`, `SOME`, `ANY` and `ALL`. Consider the following example: You are interested in removing records from a table using deleteMany. However, the criterion for doing so depends on another table.

You would expect the following to work:

    >> PersonWorkplace.deleteMany(where=
       ((PersonWorkplace.q.WorkplaceID==Workplace.q.id) &
       (Workplace.q.id==SOME_ID)))

But this doesn’t work! However, you can’t do a join in a deleteMany call. To work around this issue, use `IN`:

    >> PersonWorkplace.deleteMany(where=
       IN(PersonWorkplace.q.WorkplaceID,
       Select(Workplace.q.id, Workplace.q.id==SOME_ID)))