SQL problem (forgot to change header with earlier post!).

From: Paul Linehan <linehanp(at)tcd(dot)ie>
To:
Cc: pgsql-general(at)postgresql(dot)org
Subject: SQL problem (forgot to change header with earlier post!).
Date: 2018-05-29 11:14:39
Message-ID: CAF4RT5S7AJ-Vt9KKL2vuJyu7M7yRbDFjbUWPsFFGTkW74kigkw@mail.gmail.com
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Hi all,

I have a problem that I just can't seem to solve:

I want to divide the count of one table by the count of another -
seems simple enough!
I created simple VIEWs with counts of the tables, but I just can't
grasp the logic!

DDL and DML (simplified) at the bottom of post.

I tried various combinations of things like basic SELECTs.

SELECT avg FROM ((SELECT cnt1 FROM v1)/(SELECT cnt2 FROM v2));

and I also tried to use CTEs as follows:

WITH num AS
(
SELECT cnt1 FROM v1
),
div AS
(
SELECT cnt2 FROM v2
)
SELECT (num.cnt1/div.cnt2);

Should you require any further information or if this should be on
another list, please don't hesitate to contact me and/or let me know.

I would appreciate a short explanation of where I'm going wrong also.

TIA and rgs,

Pól...

================== DDL and DML

CREATE TABLE t1 (x INT);

INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);
INSERT INTO t1 VALUES (4);

CREATE VIEW v1 AS (SELECT COUNT(*) AS cnt1 FROM t1);

CREATE TABLE t2 (y INT);

INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);
INSERT INTO t2 VALUES (5);

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