zmVault/timestamped/2026-03-31_07-43-16.md

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id	aliases	title	tags	dg-publish	date-created	daily	weekly	monthly	quarterly	yearly
2026-03-31T07:43:16-04:00		2026-03-31 07:43:16	authorship/original destiny/permanent status/draft type/periodic/timestamped	true	2026-03-31T07:43:16-04:00	2026-03-31	2026-W14	2026-03	2026-Q1	2026

2026-03-31 07:43:16

SQL Patterns to Implement

Cross Join

In sql, the CROSS JOIN operation returns the cartesian product of two tables.

CREATE TABLE WireSizes (wire_size TEXT NOT NULL);
INSERT INTO WireSizes VALUES ('#12'), ('#10'), ('#8'), ('#6'), ('#4'), ('#2'), ('#1'), ('#1/0'), ('#2/0');

CREATE TABLE WireMaterials (wire_material TEXT NOT NULL);
INSERT INTO WireMaterials VALUES ('CU'), ('AL');

SELECT wire_size, wire_material
FROM WireSizes
CROSS JOIN WireMaterials;

SELECT wire_size||' '||wire_material AS wire_type
FROM WireSizes, WireMaterials; -- implicit cross join

Create Table From Query

CREATE TABLE _ AS syntax is intuitive,

CREATE TABLE Wires AS
SELECT wire_size, wire_material
FROM WireSizes, WireMaterials;

but it excludes the ability to set constraints.

Use this pattern instead:

CREATE TABLE Wires (
    wire_size TEXT NOT NULL,
    wire_material TEXT NOT NULL,
    PRIMARY KEY (wire_size, wire_material),
    FOREIGN KEY (wire_size) REFERENCES WireSizes(wire_size),
    FOREIGN KEY (wire_material) REFERENCES WireMaterials(wire_material)
);

INSERT INTO Wires (wire_size, wire_material)
SELECT wire_size, wire_material
FROM WireSizes, WireMaterials;

You'd think you could just throw an AS after the constraints and omit the INSERT statement, but no.

Add Columns to Table

for adding data after creating new tables with #Cross Join

ALTER TABLE Wires
ADD length_specific_dc_resistance_in_milliohms_per_foot FLOAT;

UPDATE Wires
SET length_specific_dc_resistance_in_milliohms_per_foot = CASE
   WHEN wire_size = '#8' AND wire_material = 'CU' THEN 0.778
   WHEN wire_size = '#6' AND wire_material = 'CU' THEN 0.491
   WHEN wire_size = '#4' AND wire_material = 'CU' THEN 0.308
   -- ...
   ELSE NULL
END;

Resources

• sqlshack.com