topn

Author: nigelbayliss

optimizer/topn/README.md

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+
+Some example Approximate Top-N queries available since Oracle Datatbase 18c.

optimizer/topn/eg1.sql

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+ELECT deptno, job, APPROX_SUM(sal),
+       APPROX_RANK(partition by deptno ORDER BY APPROX_SUM(sal) desc) rk
+FROM   emp
+GROUP BY deptno, job
+HAVING APPROX_RANK(partition by deptno ORDER BY APPROX_SUM(sal) desc) <= 10;
+

optimizer/topn/eg2.sql

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+connect scott/tiger 
+
+SELECT deptno, job, APPROX_SUM(sal), APPROX_COUNT(*)
+FROM   emp
+GROUP BY deptno, job
+HAVING APPROX_RANK(partition by deptno ORDER BY APPROX_SUM(sal) desc) <= 2
+AND    APPROX_RANK(partition by deptno ORDER BY APPROX_COUNT(*) desc) <= 3;
+

optimizer/topn/eg3.sql

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+connect scott/tiger
+
+SELECT deptno, job, APPROX_SUM(sal) sum_sal,
+       APPROX_SUM(sal,'MAX_ERROR') sum_sal_err
+FROM   emp
+GROUP BY deptno, job
+HAVING APPROX_RANK(partition by deptno ORDER BY APPROX_SUM(sal) desc) <= 2;