NEW Add sql UNION abstraction #1631

Job	Run time
CI / Context	2s
CI / Generate matrix	13s
CI / Check governance	1s
CI / 8.1 prf-low mysql57 phpunit framework-core	5m 15s
CI / 8.1 mysql57 phpunit framework-core	4m 57s
CI / 8.2 mysql80 phpunit framework-core	10m 28s
CI / 8.1 prf-low mysql57 phpunit framework-orm	11m 19s
CI / 8.1 mysql57 phpunit framework-orm	13m 9s
CI / 8.2 mysql80 phpunit framework-orm	13m 23s
CI / 8.1 prf-low mysql57 phpunit cms	2m 2s
CI / 8.1 mysql57 phpunit cms	1m 30s
CI / 8.2 mysql80 phpunit cms	2m 27s
CI / 8.1 mysql57 phplinting	1m 40s
CI / Check unreleased changes	0s
CI / Patch release	0s
	1h 6m 26s

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