SET custom_a = 5;
SET custom_b = -177;
SET custom_c = 98.11;
SET custom_d = 'abc def';
SELECT getSetting('custom_a') as v, toTypeName(v);
SELECT getSetting('custom_b') as v, toTypeName(v);
SELECT getSetting('custom_c') as v, toTypeName(v);
SELECT getSetting('custom_d') as v, toTypeName(v);
SELECT name, value FROM system.settings WHERE name LIKE 'custom_%' ORDER BY name;

SET custom_a = 'changed';
SET custom_b = NULL;
SET custom_c = 50000;
SET custom_d = 1.11;
SELECT getSetting('custom_a') as v, toTypeName(v);
SELECT getSetting('custom_b') as v, toTypeName(v);
SELECT getSetting('custom_c') as v, toTypeName(v);
SELECT getSetting('custom_d') as v, toTypeName(v);
SELECT name, value FROM system.settings WHERE name LIKE 'custom_%' ORDER BY name;

SELECT getSetting('custom_e') as v, toTypeName(v); -- { serverError 115 } -- Setting not found.
SET custom_e = 0;
SELECT getSetting('custom_e') as v, toTypeName(v);

SET invalid_custom = 8; -- { serverError 115 } -- Setting is neither a builtin nor started with one of the registered prefixes for user-defined settings.