How to get results in MYSQL:
If the first selection has more than 0 rows, return the result, otherwise return the result of the second selection ( is not the same table , there is only one column in the two selections).
Something similar
SELECT IF ((EXISTS(SELECT COLUMN 1 FROM TABLE 1)),(SELECT COLUMN 1 FROM TABLE 1),(SELECT COLUMN 1 FROM TABLE 2);
1
0
0
You can use the joint trick here:
WITH cte AS (
SELECT Column1, 1 AS pos FROM Table1
UNION ALL
SELECT Column1, 2 FROM Table2
)
SELECT Column1
FROM cte
WHERE
pos = 1 OR
NOT EXISTS (SELECT 1 FROM cte WHERE pos = 1);
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