sketch of a DSL for generating SQL in PHP

relsql.php

<?php
$emp = Relation('emp');
$dept = Relation('dept');

/*
 * SELECT *
 * FROM emp
 * WHERE rownum <= 5;
 */
select($emp, $emp->field('rownum')->lte(5))

/*
 * SELECT *
 * FROM dept
 * WHERE deptno NOT IN
 *    (SELECT deptno
 *     FROM emp) 
 */
select($dept, $dept->field('deptno')->notIn(project($emp, 'deptno')))

/*
 * SELECT *
 * FROM emp MINUS
 * SELECT *
 * FROM emp
 * WHERE rownum <=
 *    (SELECT COUNT(*) - 5
 *     FROM emp)
 */
difference($emp, select($emp, $emp->field('rownum')->lte(select(project($emp, Count(All())->sub(5))))))

/*
 * SELECT DISTINCT sal
 * FROM emp a
 * WHERE 3 >=
 *    (SELECT count(DISTINCT sal)
 *     FROM emp b
 *     WHERE a.sal <= b.sal)
 * ORDER BY a.sal DESC;
 */
$a = rename($emp, 'a')
$b = rename($emp, 'b')
$a_sal = $a->field('sal');
$b_sal = $b->field('sal');
$expr = select(project($a, Distinct($a_sal)), select(project($b, Count(Distinct($b_sal))), $a_sal->lte($b_sal))->lte(3))
// Alternatively, use GTE directly
// $expr = select(project($a, Distinct($a_sal)), GTE(3, select(project($b, Count(Distinct($b_sal))), $a_sal->lte($b_sal))))
$expr = Ordering($expr, $a_sal, Ordering::DESC)